From 1c123a75e9b17858b783fbc6533417bdfa9794eb Mon Sep 17 00:00:00 2001
From: Johannes Stoelp <johannes.stoelp@gmail.com>
Date: Mon, 19 Dec 2022 18:54:41 +0100
Subject: Migrate pages with assets according to zola best practice

https://www.getzola.org/documentation/content/overview/#asset-colocation
---
 content/2019-10-27-kernel-debugging-qemu.md        | 225 -------------
 content/2019-10-27-kernel-debugging-qemu/index.md  | 225 +++++++++++++
 content/2021-05-15-pthread_cancel-noexcept.md      | 110 ------
 .../2021-05-15-pthread_cancel-noexcept/index.md    | 110 ++++++
 content/2021-12-02-toying-with-virtio.md           | 373 ---------------------
 content/2021-12-02-toying-with-virtio/index.md     | 373 +++++++++++++++++++++
 content/2022-06-18-libclang-c-to-llvm-ir.md        |  32 --
 content/2022-06-18-libclang-c-to-llvm-ir/index.md  |  32 ++
 content/2022-07-07-llvm-orc-jit.md                 |  42 ---
 content/2022-07-07-llvm-orc-jit/index.md           |  42 +++
 10 files changed, 782 insertions(+), 782 deletions(-)
 delete mode 100644 content/2019-10-27-kernel-debugging-qemu.md
 create mode 100644 content/2019-10-27-kernel-debugging-qemu/index.md
 delete mode 100644 content/2021-05-15-pthread_cancel-noexcept.md
 create mode 100644 content/2021-05-15-pthread_cancel-noexcept/index.md
 delete mode 100644 content/2021-12-02-toying-with-virtio.md
 create mode 100644 content/2021-12-02-toying-with-virtio/index.md
 delete mode 100644 content/2022-06-18-libclang-c-to-llvm-ir.md
 create mode 100644 content/2022-06-18-libclang-c-to-llvm-ir/index.md
 delete mode 100644 content/2022-07-07-llvm-orc-jit.md
 create mode 100644 content/2022-07-07-llvm-orc-jit/index.md

diff --git a/content/2019-10-27-kernel-debugging-qemu.md b/content/2019-10-27-kernel-debugging-qemu.md
deleted file mode 100644
index 518b3d5..0000000
--- a/content/2019-10-27-kernel-debugging-qemu.md
+++ /dev/null
@@ -1,225 +0,0 @@
-+++
-title = "Linux Kernel debugging with QEMU"
-
-[taxonomies]
-tags = ["linux", "qemu"]
-+++
-
-**EDIT**:
-- 2021-07-15: Added `Appendix: Dockerfile for Kernel development` and updated
-  busybox + Kernel versions.
-
-The other evening while starring at some Linux kernel code I thought, let me
-setup a minimal environment so I can easily step through the code and examine
-the state.
-
-I ended up creating:
-- a [Linux kernel][linux-kernel] with minimal configuration
-- a minimal [ramdisk][initrd] to boot into which is based on [busybox][busybox]
-
-In the remaing part of this article we will go through each step by first
-building the kernel, then building the initrd and then running the kernel using
-[QEMU][qemu] and debugging it with [GDB][gdb].
-
-## $> make kernel
-
-Before building the kernel we first need to generate a configuration. As a
-starting point we generate a minimal config with the `make tinyconfig` make
-target. Running this command will generate a `.config` file. After generating
-the initial config file we customize the kernel using the merge fragment flow.
-This allows us to merge a fragment file into the current configuration by
-running the `scripts/kconfig/merge_config.sh` script.
-
-Let's quickly go over some customizations we do.
-The following two lines enable support for gzipped initramdisks:
-```config
-CONFIG_BLK_DEV_INITRD=y
-CONFIG_RD_GZIP=y
-```
-The next two configurations are important as they enable the binary loaders for
-[ELF][binfmt-elf] and [script #!][binfmt-script] files.
-```config
-CONFIG_BINFMT_ELF=y
-CONFIG_BINFMT_SCRIPT=y
-```
-
-> Note: In the cursed based configuration `make menuconfig` we can search for
-> configurations using the `/` key and then select a match using the number keys.
-> After selecting a match we can check the `Help` to get a description for the
-> configuration parameter.
-
-Building the kernel with the default make target will give us the following two
-files:
-- `vmlinux` statically linked kernel (ELF file) containing symbol information for debugging
-- `arch/x86_64/boot/bzImage` compressed kernel image for booting
-
-Full configure & build script:
-```sh
-{{ include(path="content/2019-10-27-kernel-debugging-qemu/build_kernel.sh") }}
-```
-
-## $> make initrd
-
-Next step is to build the initrd which we base on [busybox][busybox]. Therefore
-we first build the busybox project in its default configuration with one
-change, we enable following configuration to build a static binary so it can be
-used stand-alone:
-```sh
-sed -i 's/# CONFIG_STATIC .*/CONFIG_STATIC=y/' .config
-```
-
-One important step before creating the final initrd is to create an init
-process. This will be the first process executed in userspace after the kernel
-finished its initialization. We just create a script that drops us into a
-shell:
-```sh
-cat <<EOF > init
-#!/bin/sh
-
-mount -t proc none /proc
-mount -t sysfs none /sys
-
-exec setsid cttyhack sh
-EOF
-```
-> By default the kernel looks for `/sbin/init` in the root file system, but the
-> location can optionally be specified with the [`init=`][kernel-param] kernel
-> parameter.
-
-Full busybox & initrd build script:
-```sh
-{{ include(path="content/2019-10-27-kernel-debugging-qemu/build_initrd.sh") }}
-```
-
-## Running QEMU && GDB
-
-After finishing the previous steps we have all we need to run and debug the
-kernel. We have `arch/x86/boot/bzImage` and `initramfs.cpio.gz` to boot the
-kernel into a shell and we have `vmlinux` to feed the debugger with debug
-symbols.
-
-We start QEMU as follows, thanks to the `-S` flag the CPU will freeze until we
-connected the debugger:
-```sh
-# -S    freeze CPU until debugger connected
-> qemu-system-x86_64                                                 \
-  -kernel ./linux-5.3.7/arch/x86/boot/bzImage                        \
-  -nographic                                                         \
-  -append "earlyprintk=ttyS0 console=ttyS0 nokaslr init=/init debug" \
-  -initrd ./initramfs.cpio.gz                                        \
-  -gdb tcp::1234                                                     \
-  -S
-```
-
-Then we can start GDB and connect to the GDB server running in QEMU (configured
-via `-gdb tcp::1234`). From now on we can start to debug through the
-kernel.
-```sh
-> gdb linux-5.3.7/vmlinux -ex 'target remote :1234'
-(gdb) b do_execve
-Breakpoint 1 at 0xffffffff810a1a60: file fs/exec.c, line 1885.
-(gdb) c
-Breakpoint 1, do_execve (filename=0xffff888000060000, __argv=0xffffffff8181e160 <argv_init>, __envp=0xffffffff8181e040 <envp_init>) at fs/exec.c:1885
-1885          return do_execveat_common(AT_FDCWD, filename, argv, envp, 0);
-(gdb) bt
-#0  do_execve (filename=0xffff888000060000, __argv=0xffffffff8181e160 <argv_init>, __envp=0xffffffff8181e040 <envp_init>) at fs/exec.c:1885
-#1  0xffffffff81000498 in run_init_process (init_filename=<optimized out>) at init/main.c:1048
-#2  0xffffffff81116b75 in kernel_init (unused=<optimized out>) at init/main.c:1129
-#3  0xffffffff8120014f in ret_from_fork () at arch/x86/entry/entry_64.S:352
-#4  0x0000000000000000 in ?? ()
-(gdb)
-```
-
----
-
-## Appendix: Try to get around `<optimized out>`
-
-When debugging the kernel we often face following situation in gdb:
-```
-(gdb) frame
-#0  do_execveat_common (fd=fd@entry=-100, filename=0xffff888000120000, argv=argv@entry=..., envp=envp@entry=..., flags=flags@entry=0) at fs/exec.c
-
-(gdb) info args
-fd = <optimized out>
-filename = 0xffff888000060000
-argv = <optimized out>
-envp = <optimized out>
-flags = <optimized out>
-file = 0x0
-```
-The problem is that the Linux kernel requires certain code to be compiled with
-optimizations enabled.
-
-In this situation we can "try" to reduce the optimization for single compilation
-units or a subtree (try because, reducing the optimization could break the
-build). To do so we adapt the Makefile in the corresponding directory.
-```make
-# fs/Makefile
-
-# configure for single compilation unit
-CFLAGS_exec.o := -Og
-
-# configure for the whole subtree of where the Makefile resides
-ccflags-y := -Og
-```
-
-After enabling optimize for debug experience `-Og` we can see the following now
-in gdb:
-```
-(gdb) frame
-#0  do_execveat_common (fd=fd@entry=-100, filename=0xffff888000120000, argv=argv@entry=..., envp=envp@entry=..., flags=flags@entry=0) at fs/exec.c
-
-(gdb) info args
-fd = -100
-filename = 0xffff888000120000
-argv = {ptr = {native = 0x10c5980}}
-envp = {ptr = {native = 0x10c5990}}
-flags = 0
-
-(gdb) p *filename
-$3 = {name = 0xffff888000120020 "/bin/ls", uptr = 0x10c59b8 "/bin/ls", refcnt = 1, aname = 0x0, iname = 0xffff888000120020 "/bin/ls"}
-
-(gdb) ptype filename
-type = struct filename {
-    const char *name;
-    const char *uptr;
-    int refcnt;
-    struct audit_names *aname;
-    const char iname[];
-}
-```
-
-## Appendix: `Dockerfile` for Kernel development
-
-The following `Dockerfile` provides a development environment with all the
-required tools and dependencies, to re-produce all the steps of building and
-debugging the Linux kernel.
-```dockerfile
-{{ include(path="content/2019-10-27-kernel-debugging-qemu/Dockerfile") }}
-```
-
-Save the listing above in a file called `Dockerfile` and build the docker image
-as follows.
-```sh
-docker build -t kernel-dev
-```
-> Optionally set `DOCKER_BUILDKIT=1` to use the newer image builder.
-
-Once the image has been built, an interactive container can be launched as
-follows.
-```sh
-# Some options for conveniene:
-#   -v <HOST>:<GUEST>     Mount host path to guest path.
-#   --rm                  Remove the container after exiting.
-
-docker run -it kernel-dev
-```
-
-[linux-kernel]: https://www.kernel.org
-[initrd]: https://www.kernel.org/doc/html/latest/admin-guide/initrd.html
-[busybox]: https://busybox.net
-[qemu]: https://www.qemu.org
-[gdb]: https://www.gnu.org/software/gdb
-[binfmt-elf]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/binfmt_elf.c
-[binfmt-script]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/binfmt_script.c
-[kernel-param]: https://www.kernel.org/doc/html/latest/admin-guide/kernel-parameters.html
diff --git a/content/2019-10-27-kernel-debugging-qemu/index.md b/content/2019-10-27-kernel-debugging-qemu/index.md
new file mode 100644
index 0000000..518b3d5
--- /dev/null
+++ b/content/2019-10-27-kernel-debugging-qemu/index.md
@@ -0,0 +1,225 @@
++++
+title = "Linux Kernel debugging with QEMU"
+
+[taxonomies]
+tags = ["linux", "qemu"]
++++
+
+**EDIT**:
+- 2021-07-15: Added `Appendix: Dockerfile for Kernel development` and updated
+  busybox + Kernel versions.
+
+The other evening while starring at some Linux kernel code I thought, let me
+setup a minimal environment so I can easily step through the code and examine
+the state.
+
+I ended up creating:
+- a [Linux kernel][linux-kernel] with minimal configuration
+- a minimal [ramdisk][initrd] to boot into which is based on [busybox][busybox]
+
+In the remaing part of this article we will go through each step by first
+building the kernel, then building the initrd and then running the kernel using
+[QEMU][qemu] and debugging it with [GDB][gdb].
+
+## $> make kernel
+
+Before building the kernel we first need to generate a configuration. As a
+starting point we generate a minimal config with the `make tinyconfig` make
+target. Running this command will generate a `.config` file. After generating
+the initial config file we customize the kernel using the merge fragment flow.
+This allows us to merge a fragment file into the current configuration by
+running the `scripts/kconfig/merge_config.sh` script.
+
+Let's quickly go over some customizations we do.
+The following two lines enable support for gzipped initramdisks:
+```config
+CONFIG_BLK_DEV_INITRD=y
+CONFIG_RD_GZIP=y
+```
+The next two configurations are important as they enable the binary loaders for
+[ELF][binfmt-elf] and [script #!][binfmt-script] files.
+```config
+CONFIG_BINFMT_ELF=y
+CONFIG_BINFMT_SCRIPT=y
+```
+
+> Note: In the cursed based configuration `make menuconfig` we can search for
+> configurations using the `/` key and then select a match using the number keys.
+> After selecting a match we can check the `Help` to get a description for the
+> configuration parameter.
+
+Building the kernel with the default make target will give us the following two
+files:
+- `vmlinux` statically linked kernel (ELF file) containing symbol information for debugging
+- `arch/x86_64/boot/bzImage` compressed kernel image for booting
+
+Full configure & build script:
+```sh
+{{ include(path="content/2019-10-27-kernel-debugging-qemu/build_kernel.sh") }}
+```
+
+## $> make initrd
+
+Next step is to build the initrd which we base on [busybox][busybox]. Therefore
+we first build the busybox project in its default configuration with one
+change, we enable following configuration to build a static binary so it can be
+used stand-alone:
+```sh
+sed -i 's/# CONFIG_STATIC .*/CONFIG_STATIC=y/' .config
+```
+
+One important step before creating the final initrd is to create an init
+process. This will be the first process executed in userspace after the kernel
+finished its initialization. We just create a script that drops us into a
+shell:
+```sh
+cat <<EOF > init
+#!/bin/sh
+
+mount -t proc none /proc
+mount -t sysfs none /sys
+
+exec setsid cttyhack sh
+EOF
+```
+> By default the kernel looks for `/sbin/init` in the root file system, but the
+> location can optionally be specified with the [`init=`][kernel-param] kernel
+> parameter.
+
+Full busybox & initrd build script:
+```sh
+{{ include(path="content/2019-10-27-kernel-debugging-qemu/build_initrd.sh") }}
+```
+
+## Running QEMU && GDB
+
+After finishing the previous steps we have all we need to run and debug the
+kernel. We have `arch/x86/boot/bzImage` and `initramfs.cpio.gz` to boot the
+kernel into a shell and we have `vmlinux` to feed the debugger with debug
+symbols.
+
+We start QEMU as follows, thanks to the `-S` flag the CPU will freeze until we
+connected the debugger:
+```sh
+# -S    freeze CPU until debugger connected
+> qemu-system-x86_64                                                 \
+  -kernel ./linux-5.3.7/arch/x86/boot/bzImage                        \
+  -nographic                                                         \
+  -append "earlyprintk=ttyS0 console=ttyS0 nokaslr init=/init debug" \
+  -initrd ./initramfs.cpio.gz                                        \
+  -gdb tcp::1234                                                     \
+  -S
+```
+
+Then we can start GDB and connect to the GDB server running in QEMU (configured
+via `-gdb tcp::1234`). From now on we can start to debug through the
+kernel.
+```sh
+> gdb linux-5.3.7/vmlinux -ex 'target remote :1234'
+(gdb) b do_execve
+Breakpoint 1 at 0xffffffff810a1a60: file fs/exec.c, line 1885.
+(gdb) c
+Breakpoint 1, do_execve (filename=0xffff888000060000, __argv=0xffffffff8181e160 <argv_init>, __envp=0xffffffff8181e040 <envp_init>) at fs/exec.c:1885
+1885          return do_execveat_common(AT_FDCWD, filename, argv, envp, 0);
+(gdb) bt
+#0  do_execve (filename=0xffff888000060000, __argv=0xffffffff8181e160 <argv_init>, __envp=0xffffffff8181e040 <envp_init>) at fs/exec.c:1885
+#1  0xffffffff81000498 in run_init_process (init_filename=<optimized out>) at init/main.c:1048
+#2  0xffffffff81116b75 in kernel_init (unused=<optimized out>) at init/main.c:1129
+#3  0xffffffff8120014f in ret_from_fork () at arch/x86/entry/entry_64.S:352
+#4  0x0000000000000000 in ?? ()
+(gdb)
+```
+
+---
+
+## Appendix: Try to get around `<optimized out>`
+
+When debugging the kernel we often face following situation in gdb:
+```
+(gdb) frame
+#0  do_execveat_common (fd=fd@entry=-100, filename=0xffff888000120000, argv=argv@entry=..., envp=envp@entry=..., flags=flags@entry=0) at fs/exec.c
+
+(gdb) info args
+fd = <optimized out>
+filename = 0xffff888000060000
+argv = <optimized out>
+envp = <optimized out>
+flags = <optimized out>
+file = 0x0
+```
+The problem is that the Linux kernel requires certain code to be compiled with
+optimizations enabled.
+
+In this situation we can "try" to reduce the optimization for single compilation
+units or a subtree (try because, reducing the optimization could break the
+build). To do so we adapt the Makefile in the corresponding directory.
+```make
+# fs/Makefile
+
+# configure for single compilation unit
+CFLAGS_exec.o := -Og
+
+# configure for the whole subtree of where the Makefile resides
+ccflags-y := -Og
+```
+
+After enabling optimize for debug experience `-Og` we can see the following now
+in gdb:
+```
+(gdb) frame
+#0  do_execveat_common (fd=fd@entry=-100, filename=0xffff888000120000, argv=argv@entry=..., envp=envp@entry=..., flags=flags@entry=0) at fs/exec.c
+
+(gdb) info args
+fd = -100
+filename = 0xffff888000120000
+argv = {ptr = {native = 0x10c5980}}
+envp = {ptr = {native = 0x10c5990}}
+flags = 0
+
+(gdb) p *filename
+$3 = {name = 0xffff888000120020 "/bin/ls", uptr = 0x10c59b8 "/bin/ls", refcnt = 1, aname = 0x0, iname = 0xffff888000120020 "/bin/ls"}
+
+(gdb) ptype filename
+type = struct filename {
+    const char *name;
+    const char *uptr;
+    int refcnt;
+    struct audit_names *aname;
+    const char iname[];
+}
+```
+
+## Appendix: `Dockerfile` for Kernel development
+
+The following `Dockerfile` provides a development environment with all the
+required tools and dependencies, to re-produce all the steps of building and
+debugging the Linux kernel.
+```dockerfile
+{{ include(path="content/2019-10-27-kernel-debugging-qemu/Dockerfile") }}
+```
+
+Save the listing above in a file called `Dockerfile` and build the docker image
+as follows.
+```sh
+docker build -t kernel-dev
+```
+> Optionally set `DOCKER_BUILDKIT=1` to use the newer image builder.
+
+Once the image has been built, an interactive container can be launched as
+follows.
+```sh
+# Some options for conveniene:
+#   -v <HOST>:<GUEST>     Mount host path to guest path.
+#   --rm                  Remove the container after exiting.
+
+docker run -it kernel-dev
+```
+
+[linux-kernel]: https://www.kernel.org
+[initrd]: https://www.kernel.org/doc/html/latest/admin-guide/initrd.html
+[busybox]: https://busybox.net
+[qemu]: https://www.qemu.org
+[gdb]: https://www.gnu.org/software/gdb
+[binfmt-elf]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/binfmt_elf.c
+[binfmt-script]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/binfmt_script.c
+[kernel-param]: https://www.kernel.org/doc/html/latest/admin-guide/kernel-parameters.html
diff --git a/content/2021-05-15-pthread_cancel-noexcept.md b/content/2021-05-15-pthread_cancel-noexcept.md
deleted file mode 100644
index f09cadc..0000000
--- a/content/2021-05-15-pthread_cancel-noexcept.md
+++ /dev/null
@@ -1,110 +0,0 @@
-+++
-title = "pthread_cancel in c++ code"
-
-[taxonomies]
-tags = ["linux", "threading", "c++"]
-+++
-
-Few weeks ago I was debugging a random crash in a legacy code base at work. In
-case the crash occurred the following message was printed on `stdout` of the
-process:
-```
-terminate called without an active exception
-```
-
-Looking at the reasons when [`std::terminate()`][std_terminate] is being
-called, and the message that `std::terminate()` was called without an active
-exception, the initial assumption was one of the following:
-- `10) a joinable std::thread is destroyed or assigned to`.
-- Invoked explicitly by the user.
-
-After receiving a backtrace captured by a customer it wasn't directly obvious
-to me why `std::terminate()` was called here. The backtrace received looked
-something like the following:
-```
-#0  0x00007fb21df22ef5 in raise () from /usr/lib/libc.so.6
-#1  0x00007fb21df0c862 in abort () from /usr/lib/libc.so.6
-#2  0x00007fb21e2a886a in __gnu_cxx::__verbose_terminate_handler () at /build/gcc/src/gcc/libstdc++-v3/libsupc++/vterminate.cc:95
-#3  0x00007fb21e2b4d3a in __cxxabiv1::__terminate (handler=<optimized out>) at /build/gcc/src/gcc/libstdc++-v3/libsupc++/eh_terminate.cc:48
-#4  0x00007fb21e2b4da7 in std::terminate () at /build/gcc/src/gcc/libstdc++-v3/libsupc++/eh_terminate.cc:58
-#5  0x00007fb21e2b470d in __cxxabiv1::__gxx_personality_v0 (version=<optimized out>, actions=10, exception_class=0, ue_header=0x7fb21dee0cb0,  context=<optimized out>) at /build/gcc/src/gcc/libstdc++-v3/libsupc++/eh_personality.cc:673
-#6  0x00007fb21e0c3814 in _Unwind_ForcedUnwind_Phase2 (exc=0x7fb21dee0cb0, context=0x7fb21dedfc50, frames_p=0x7fb21dedfb58) at /build/gcc/src/gcc/libgcc/unwind.inc:182
-#7  0x00007fb21e0c3f12 in _Unwind_ForcedUnwind (exc=0x7fb21dee0cb0, stop=<optimized out>, stop_argument=0x7fb21dedfe70) at /build/gcc/src/gcc/libgcc/unwind.inc:217
-#8  0x00007fb21e401434 in __pthread_unwind () from /usr/lib/libpthread.so.0
-#9  0x00007fb21e401582 in __pthread_enable_asynccancel () from /usr/lib/libpthread.so.0
-#10 0x00007fb21e4017c7 in write () from /usr/lib/libpthread.so.0
-#11 0x000055f6b8149320 in S::~S (this=0x7fb21dedfe37, __in_chrg=<optimized out>) at 20210515-pthread_cancel-noexcept/thread.cc:9
-#12 0x000055f6b81491bb in threadFn () at 20210515-pthread_cancel-noexcept/thread.cc:18
-#13 0x00007fb21e3f8299 in start_thread () from /usr/lib/libpthread.so.0
-#14 0x00007fb21dfe5053 in clone () from /usr/lib/libc.so.6
-```
-Looking at frames `#6 - #9` we can see that the crashing thread is just
-executing `forced unwinding` which is performing the stack unwinding as part of
-the thread being cancelled by [`pthread_cancel(3)`][pthread_cancel].
-Thread cancellation starts here from the call to `write()` at frame `#10`, as
-pthreads in their default configuration only perform thread cancellation
-requests when passing a `cancellation point` as described in
-[pthreads(7)][pthreads].
-> The pthread cancel type can either be `PTHREAD_CANCEL_DEFERRED (default)` or
-> `PTHREAD_CANCEL_ASYNCHRONOUS` and can be set with
-> [`pthread_setcanceltype(3)`][pthread_canceltype].
-
-With this findings we can take another look at the reasons when
-[`std::terminate()`][std_terminate] is being called. The interesting item on
-the list this time is the following:
-- `7) a noexcept specification is violated`
-
-This item is of particular interest because:
-- In c++ `destructors` are implicitly marked [`noexcept`][noexcept].
-- For NPTL, thread cancellation is implemented by throwing an exception of type
-  `abi::__forced_unwind`.
-
-With all these findings, the random crash in the application can be explained
-as that the `pthread_cancel` call was happening asynchronous to the cancelled
-thread and there was a chance that a `cancellation point` was hit in a
-`destructor`.
-
-## Conclusion
-In general `pthread_cancel` should not be used in c++ code at all, but the
-thread should have a way to request a clean shutdown (for example similar to
-[`std::jthread`][jthread]).
-
-However if thread cancellation is **required** then the code should be audited
-very carefully and the cancellation points controlled explicitly. This can be
-achieved by inserting cancellation points at **safe** sections as:
-```c
-pthread_setcancelstate(PTHREAD_CANCEL_ENABLE);
-pthread_testcancel();
-pthread_setcancelstate(PTHREAD_CANCEL_DISABLE);
-```
-> On thread entry, the cancel state should be set to `PTHREAD_CANCEL_DISABLE`
-> to disable thread cancellation.
-
-## Appendix: `abi::__forced_unwind` exception
-As mentioned above, thread cancellation for NPTL is implemented by throwing an
-exception of type `abi::__forced_unwind`. This exception can actually be caught
-in case some extra clean-up steps need to be performed on thread cancellation.
-However it is **required** to `rethrow` the exception.
-```cpp
-#include <cxxabi.h>
-
-try {
-    // ...
-} catch (abi::__forced_unwind&) {
-    // Do some extra cleanup.
-    throw;
-}
-```
-
-## Appendix: Minimal reproducer
-```cpp
-{{ include(path="content/2021-05-15-pthread_cancel-noexcept/thread.cc") }}
-```
-
-[std_terminate]: https://en.cppreference.com/w/cpp/error/terminate
-[pthread_cancel]: https://man7.org/linux/man-pages/man3/pthread_cancel.3.html
-[pthread_canceltype]: https://man7.org/linux/man-pages/man3/pthread_setcanceltype.3.html
-[pthread_testcancel]: https://man7.org/linux/man-pages/man3/pthread_testcancel.3.html
-[pthreads]: https://man7.org/linux/man-pages/man7/pthreads.7.html
-[noexcept]: https://en.cppreference.com/w/cpp/language/noexcept_spec
-[jthread]: https://en.cppreference.com/w/cpp/thread/jthread/request_stop
diff --git a/content/2021-05-15-pthread_cancel-noexcept/index.md b/content/2021-05-15-pthread_cancel-noexcept/index.md
new file mode 100644
index 0000000..f09cadc
--- /dev/null
+++ b/content/2021-05-15-pthread_cancel-noexcept/index.md
@@ -0,0 +1,110 @@
++++
+title = "pthread_cancel in c++ code"
+
+[taxonomies]
+tags = ["linux", "threading", "c++"]
++++
+
+Few weeks ago I was debugging a random crash in a legacy code base at work. In
+case the crash occurred the following message was printed on `stdout` of the
+process:
+```
+terminate called without an active exception
+```
+
+Looking at the reasons when [`std::terminate()`][std_terminate] is being
+called, and the message that `std::terminate()` was called without an active
+exception, the initial assumption was one of the following:
+- `10) a joinable std::thread is destroyed or assigned to`.
+- Invoked explicitly by the user.
+
+After receiving a backtrace captured by a customer it wasn't directly obvious
+to me why `std::terminate()` was called here. The backtrace received looked
+something like the following:
+```
+#0  0x00007fb21df22ef5 in raise () from /usr/lib/libc.so.6
+#1  0x00007fb21df0c862 in abort () from /usr/lib/libc.so.6
+#2  0x00007fb21e2a886a in __gnu_cxx::__verbose_terminate_handler () at /build/gcc/src/gcc/libstdc++-v3/libsupc++/vterminate.cc:95
+#3  0x00007fb21e2b4d3a in __cxxabiv1::__terminate (handler=<optimized out>) at /build/gcc/src/gcc/libstdc++-v3/libsupc++/eh_terminate.cc:48
+#4  0x00007fb21e2b4da7 in std::terminate () at /build/gcc/src/gcc/libstdc++-v3/libsupc++/eh_terminate.cc:58
+#5  0x00007fb21e2b470d in __cxxabiv1::__gxx_personality_v0 (version=<optimized out>, actions=10, exception_class=0, ue_header=0x7fb21dee0cb0,  context=<optimized out>) at /build/gcc/src/gcc/libstdc++-v3/libsupc++/eh_personality.cc:673
+#6  0x00007fb21e0c3814 in _Unwind_ForcedUnwind_Phase2 (exc=0x7fb21dee0cb0, context=0x7fb21dedfc50, frames_p=0x7fb21dedfb58) at /build/gcc/src/gcc/libgcc/unwind.inc:182
+#7  0x00007fb21e0c3f12 in _Unwind_ForcedUnwind (exc=0x7fb21dee0cb0, stop=<optimized out>, stop_argument=0x7fb21dedfe70) at /build/gcc/src/gcc/libgcc/unwind.inc:217
+#8  0x00007fb21e401434 in __pthread_unwind () from /usr/lib/libpthread.so.0
+#9  0x00007fb21e401582 in __pthread_enable_asynccancel () from /usr/lib/libpthread.so.0
+#10 0x00007fb21e4017c7 in write () from /usr/lib/libpthread.so.0
+#11 0x000055f6b8149320 in S::~S (this=0x7fb21dedfe37, __in_chrg=<optimized out>) at 20210515-pthread_cancel-noexcept/thread.cc:9
+#12 0x000055f6b81491bb in threadFn () at 20210515-pthread_cancel-noexcept/thread.cc:18
+#13 0x00007fb21e3f8299 in start_thread () from /usr/lib/libpthread.so.0
+#14 0x00007fb21dfe5053 in clone () from /usr/lib/libc.so.6
+```
+Looking at frames `#6 - #9` we can see that the crashing thread is just
+executing `forced unwinding` which is performing the stack unwinding as part of
+the thread being cancelled by [`pthread_cancel(3)`][pthread_cancel].
+Thread cancellation starts here from the call to `write()` at frame `#10`, as
+pthreads in their default configuration only perform thread cancellation
+requests when passing a `cancellation point` as described in
+[pthreads(7)][pthreads].
+> The pthread cancel type can either be `PTHREAD_CANCEL_DEFERRED (default)` or
+> `PTHREAD_CANCEL_ASYNCHRONOUS` and can be set with
+> [`pthread_setcanceltype(3)`][pthread_canceltype].
+
+With this findings we can take another look at the reasons when
+[`std::terminate()`][std_terminate] is being called. The interesting item on
+the list this time is the following:
+- `7) a noexcept specification is violated`
+
+This item is of particular interest because:
+- In c++ `destructors` are implicitly marked [`noexcept`][noexcept].
+- For NPTL, thread cancellation is implemented by throwing an exception of type
+  `abi::__forced_unwind`.
+
+With all these findings, the random crash in the application can be explained
+as that the `pthread_cancel` call was happening asynchronous to the cancelled
+thread and there was a chance that a `cancellation point` was hit in a
+`destructor`.
+
+## Conclusion
+In general `pthread_cancel` should not be used in c++ code at all, but the
+thread should have a way to request a clean shutdown (for example similar to
+[`std::jthread`][jthread]).
+
+However if thread cancellation is **required** then the code should be audited
+very carefully and the cancellation points controlled explicitly. This can be
+achieved by inserting cancellation points at **safe** sections as:
+```c
+pthread_setcancelstate(PTHREAD_CANCEL_ENABLE);
+pthread_testcancel();
+pthread_setcancelstate(PTHREAD_CANCEL_DISABLE);
+```
+> On thread entry, the cancel state should be set to `PTHREAD_CANCEL_DISABLE`
+> to disable thread cancellation.
+
+## Appendix: `abi::__forced_unwind` exception
+As mentioned above, thread cancellation for NPTL is implemented by throwing an
+exception of type `abi::__forced_unwind`. This exception can actually be caught
+in case some extra clean-up steps need to be performed on thread cancellation.
+However it is **required** to `rethrow` the exception.
+```cpp
+#include <cxxabi.h>
+
+try {
+    // ...
+} catch (abi::__forced_unwind&) {
+    // Do some extra cleanup.
+    throw;
+}
+```
+
+## Appendix: Minimal reproducer
+```cpp
+{{ include(path="content/2021-05-15-pthread_cancel-noexcept/thread.cc") }}
+```
+
+[std_terminate]: https://en.cppreference.com/w/cpp/error/terminate
+[pthread_cancel]: https://man7.org/linux/man-pages/man3/pthread_cancel.3.html
+[pthread_canceltype]: https://man7.org/linux/man-pages/man3/pthread_setcanceltype.3.html
+[pthread_testcancel]: https://man7.org/linux/man-pages/man3/pthread_testcancel.3.html
+[pthreads]: https://man7.org/linux/man-pages/man7/pthreads.7.html
+[noexcept]: https://en.cppreference.com/w/cpp/language/noexcept_spec
+[jthread]: https://en.cppreference.com/w/cpp/thread/jthread/request_stop
diff --git a/content/2021-12-02-toying-with-virtio.md b/content/2021-12-02-toying-with-virtio.md
deleted file mode 100644
index c2ff031..0000000
--- a/content/2021-12-02-toying-with-virtio.md
+++ /dev/null
@@ -1,373 +0,0 @@
-+++
-title = "QEMU virtio configurations"
-
-[taxonomies]
-tags = ["linux", "qemu", "virtio"]
-+++
-
-For my own reference I wanted to document some minimal [`virtio`][virtio]
-device configurations with qemu and the required Linux kernel configuration to
-enable those devices.
-
-The devices we will use are `virtio console`, `virtio blk` and `virtio net`.
-
-To make use of the virtio devices in qemu we are going to build and boot into
-busybox based [`initramfs`][initramfs].
-
-## Build initramfs
-
-For the initramfs there is not much magic, we will grab a copy of busybox,
-configure it with the default config (`defconfig`) and enable static linking as
-we will use it as rootfs.
-
-For the `init` process we will use the one provided by busybox but we have to
-symlink it to `/init` as during boot, the kernel will extract the cpio
-compressed initramfs into `rootfs` and look for the `/init` file. If that's not
-found the kernel will fallback to an older mechanism an try to mount a root
-partition (which we don't have).
-> Optionally the init binary could be specified with the `rdinit=` kernel boot
-> parameter.
-
-We populate the `/etc/inittab` and `/etc/init.d/rcS` with a minimal
-configuration to mount the `proc`, `sys` and `dev` filesystems and drop into a
-shell after the boot is completed. \
-Additionally we setup `/etc/passwd` and `/etc/shadow` with an entry for the
-`root` user with the password `1234`, so we can login via the virtio console
-later.
-
-```sh
-{{ include_range(path="content/2021-12-02-toying-with-virtio/build_initramfs.sh", start=31, end=67) }}
-```
-
-The full build script is available under [build_initramfs.sh][build-initramfs].
-
-## Virtio console
-
-To enable support for the virtio console we enable the kernel configs shown
-below.
-The pci configurations are enabled because in qemu the virtio console front-end
-device (the one presented to the guest) is attached to the pci bus.
-
-```sh
-{{ include_range(path="content/2021-12-02-toying-with-virtio/build_kernel.sh", start=32, end=38) }}
-```
-
-The full build script is available under [build_kernel.sh][build-kernel].
-
-To boot-up the guest we use the following qemu configuration.
-
-```sh
-qemu-system-x86_64                                            \
-  -nographic                                                  \
-  -cpu host                                                   \
-  -enable-kvm                                                 \
-  -kernel ./linux-$(VER)/arch/x86/boot/bzImage                \
-  -append "earlyprintk=ttyS0 console=ttyS0 root=/dev/ram0 ro" \
-  -initrd ./initramfs.cpio.gz                                 \
-  -device virtio-serial-pci                                   \
-  -device virtconsole,chardev=vcon,name=console.0             \
-  -chardev socket,id=vcon,ipv4=on,host=localhost,port=2222,server,telnet=on,wait=off
-```
-
-The important parts in this configuration are the last three lines.
-
-The `virtio-serial-pci` device creates the serial bus where the virtio console
-is attached to.
-
-The `virtconsole` creates the virtio console device exposed to the guest
-(front-end). The `chardev=vcon` option specifies that the chardev with
-`id=vcon` is attached as back-end to the virtio console.
-The back-end device is the one we will have access to from the host running the
-emulation.
-
-The chardev back-end we configure to be a `socket`, running a telnet server
-listening on port 2222. The `wait=off` tells qemu that it can directly boot
-without waiting for a client connection.
-
-After booting the guest we are dropped into a shell and can verify that our
-device is being detected properly.
-```sh
-root@virtio-box ~ # ls /sys/bus/virtio/devices/
-virtio0
-root@virtio-box ~ # cat /sys/bus/virtio/devices/virtio0/virtio-ports/vport0p0/name
-console.0
-```
-
-In `/etc/inittab`, we already configured to spawn `getty` on the first
-hypervisor console `/dev/hvc0`. This will effectively run `login(1)` over the
-serial console.
-
-From the host we can run `telnet localhost 2222` and are presented with a login shell to the guest.
-
-As we already included to launch `getty` on the first hypervisor console
-`/dev/hvc0` in `/etc/inittab`, we can directly connect to the back-end chardev
-and login to the guest with `root:1234`.
-
-```sh
-> telnet -4 localhost 2222
-Trying 127.0.0.1...
-Connected to localhost.
-Escape character is '^]'.
-
-virtio-box login: root
-Password:
-root@virtio-box ~ #
-```
-
-## Virtio blk
-
-To enable support for the virtio block device we enable the kernel configs
-shown below.
-First we enable general support for block devices and then for virtio block
-devices. Additionally we enable support for the `ext2` filesystem because we
-are creating an ext2 filesystem to back the virtio block device.
-
-```sh
-{{ include_range(path="content/2021-12-02-toying-with-virtio/build_kernel.sh", start=40, end=47) }}
-```
-
-The full build script is available under [build_kernel.sh][build-kernel].
-
-Next we are creating the ext2 filesystem image. This we'll do by creating an
-`128M` blob and format it with ext2 afterwards. Then we can mount the image
-via a `loop` device and populate the filesystem.
-```sh
-{{ include_range(path="content/2021-12-02-toying-with-virtio/build_ext2.sh", start=3, end=7) }}
-```
-
-Before booting the guest we will attach the virtio block device to the VM.
-Therefore we add the `-drive` configuration to our previous qemu invocation.
-
-```sh
-qemu-system-x86_64 \
-  ...
-  -drive if=virtio,file=fs.ext2,format=raw
-```
-
-The `-drive` option is a shortcut for a `-device (front-end) / -blockdev
-(back-end)` pair.
-
-The `if=virtio` flag specifies the interface of the front-end device to be
-`virtio`.
-
-The `file` and `format` flags configure the back-end to be a disk image.
-
-After booting the guest we are dropped into a shell and can verify a few
-things. First we check if the virtio block device is detected, then we check if
-we have support for the ext2 filesystem and finally we mount the disk.
-
-```sh
-root@virtio-box ~ # ls -l /sys/block/
-lrwxrwxrwx 1 root 0 0 Dec  3 22:46 vda -> ../devices/pci0000:00/0000:00:05.0/virtio1/block/vda
-
-root@virtio-box ~ # cat /proc/filesystems
-...
-       ext2
-
-root@virtio-box ~ # mount -t ext2 /dev/vda /mnt
-EXT2-fs (vda): warning: mounting unchecked fs, running e2fsck is recommended
-ext2 filesystem being mounted at /mnt supports timestamps until 2038 (0x7fffffff)
-
-root@virtio-box ~ # cat /mnt/hello
-world
-```
-
-## Virtio net
-
-To enable support for the virtio network device we enable the kernel configs
-shown below.
-First we enable general support for networking and TCP/IP and then enable the
-core networking driver and the virtio net driver.
-
-```sh
-{{ include_range(path="content/2021-12-02-toying-with-virtio/build_kernel.sh", start=49, end=62) }}
-```
-
-The full build script is available under [build_kernel.sh][build-kernel].
-
-For the qemu device emulation we already decided on the front-end device, which
-will be our virtio net device. \
-On the back-end we will choose the [`user`][qemu-user-net] option. This enables
-a network stack implemented in userspace based on [libslirp][libslirp], which
-has the benefit that we do not need to setup additional network interfaces and
-therefore require any privileges. Fundamentally, [libslirp][libslirp] works by
-replaying [Layer 2][osi-2] packets received from the guest NIC via the socket
-API on the host ([Layer 4][osi-4]) and vice versa. User networking comes with a
-set of limitations, for example
-- Can not use `ping` inside the guest as `ICMP` is not supported.
-- The guest is not accessible from the host.
-
-With the guest, qemu and the host in the picture this looks something like the
-following.
-```
-+--------------------------------------------+
-|                                       host |
-|     +-------------------------+            |
-|     | guest                   |            |
-|     |                         |            |
-|     |                    user |            |
-|     +------+------+-----------+            |
-|     |      | eth0 |    kernel |            |
-|     |      +--+---+           |            |
-|     |         |               |            |
-|     |   +-----v--------+      |            |
-|     |   | nic (virtio) |      |            |
-|  +--+---+-----+--------+------+--+         |
-|  |            | Layer 2     qemu |         |
-|  |            | (eth frames)     |         |
-|  |       +----v-----+            |         |
-|  |       | libslirp |            |         |
-|  |       +----+-----+            |         |
-|  |            | Layer 4          |         |
-|  |            | (socket API)     |    user |
-+--+---------+--v---+--------------+---------+
-|            | eth0 |                 kernel |
-|            +------+                        |
-+--------------------------------------------+
-```
-
-The user networking implements a virtually NAT'ed sub-network with the address
-range `10.0.2.0/24` running an internal dhcp server. By default, the dhcp
-server assigns the following IP addresses which are interesting to us:
-- `10.0.2.2` host running the qemu emulation
-- `10.0.2.3` virtual DNS server
-> The netdev options `net=addr/mask`, `host=addr`, `dns=addr` can be used to
-> re-configure the sub-network (see [network options][qemu-nic-opts]).
-
-With the details of the sub-network in mind we can add some additional setup to
-the initramfs which performs the basic network setup.
-
-We add the virtual DNS server to `/etc/resolv.conf` which will be used by the
-libc resolver functions.
-
-Additionally we assign a static ip to the `eth0` network interface, bring the
-interface up and define the default route via the host `10.0.2.2`.
-
-```sh
-{{ include_range(path="content/2021-12-02-toying-with-virtio/build_initramfs.sh", start=69, end=85) }}
-```
-
-The full build script is available under [build_initramfs.sh][build-initramfs].
-
-Before booting the guest we will attach the virtio net device and configure to
-use the user network stack.
-Therefore we add the `-nic` configuration to our previous qemu invocation.
-
-```sh
-qemu-system-x86_64 \
-  ...
-  -nic user,model=virtio-net-pci
-```
-
-The `-nic` option is a shortcut for a `-device (front-end) / -netdev
-(back-end)` pair.
-
-After booting the guest we are dropped into a shell and can verify a few
-things. First we check if the virtio net device is detected. Then we check if
-the interface got configured and brought up correctly.
-
-```sh
-root@virtio-box ~ # ls -l /sys/class/net/
-lrwxrwxrwx 1 root 0 0 Dec  4 16:56 eth0 -> ../../devices/pci0000:00/0000:00:03.0/virtio0/net/eth0
-lrwxrwxrwx 1 root 0 0 Dec  4 16:56 lo -> ../../devices/virtual/net/lo
-
-
-root@virtio-box ~ # ip -o a
-2: eth0    inet 10.0.2.15/24 scope global eth0  ...
-
-root@virtio-box ~ # ip route
-default via 10.0.2.2 dev eth0
-10.0.2.0/24 dev eth0 scope link  src 10.0.2.15
-```
-
-We can resolve out domain and see that the virtual DNS gets contacted.
-
-```sh
-root@virtio-box ~ # nslookup memzero.de
-Server:   10.0.2.3
-Address:  10.0.2.3:53
-
-Non-authoritative answer:
-Name:    memzero.de
-Address: 46.101.148.203
-```
-
-Additionally we can try to access a service running on the host. Therefore we
-run a simple http server on the host (where we launched qemu) with the
-following command `python3 -m http.server --bind 0.0.0.0 1234`. This will
-launch the server to listen for any incoming address at port `1234`.
-
-From within the guest we can manually craft a simple http `GET` request and
-send it to the http server running on the host. For that we use the IP address
-`10.0.2.2` which the dhcp assigned to our host.
-
-```sh
-root@virtio-box ~ # echo "GET / HTTP/1.0" | nc 10.0.2.2 1234
-HTTP/1.0 200 OK
-Server: SimpleHTTP/0.6 Python/3.9.7
-Date: Sat, 04 Dec 2021 16:58:56 GMT
-Content-type: text/html; charset=utf-8
-Content-Length: 917
-
-<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
-<html>
-<head>
-<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
-<title>Directory listing for /</title>
-</head>
-<body>
-<h1>Directory listing for /</h1>
-<hr>
-<ul>
-<li><a href="build_initramfs.sh">build_initramfs.sh</a></li>
-...
-</ul>
-<hr>
-</body>
-</html>
-```
-
-## Appendix: Workspace
-
-To re-produce the setup and play around with it just grab a copy of the
-following files:
-- [Dockerfile][dockerfile]
-- [Makefile][makefile]
-- [build_initramfs.sh][build-initramfs]
-- [build_kernel.sh][build-kernel]
-- [build_ext2.sh][build-ext2]
-
-Then run the following steps to build everything. The prefix `[H]` and `[C]`
-indicate whether this command is run on the host or inside the container
-respectively.
-```sh
-# To see all the make targets.
-[H] make help
-
-# Build docker image, start a container with the current working dir
-# mounted. On the first invocation this takes some minutes to build
-# the image.
-[H]: make docker
-
-# Build kernel and initramfs.
-[C]: make
-
-# Build ext2 fs as virtio blkdev backend.
-[H]: make ext2
-
-# Start qemu guest.
-[H]: make run
-```
-
-[build-initramfs]: https://git.memzero.de/blog/tree/content/2021-12-02-toying-with-virtio/build_initramfs.sh?h=main
-[build-kernel]: https://git.memzero.de/blog/tree/content/2021-12-02-toying-with-virtio/build_kernel.sh?h=main
-[build-ext2]: https://git.memzero.de/blog/tree/content/2021-12-02-toying-with-virtio/build_ext2.sh?h=main
-[makefile]: https://git.memzero.de/blog/tree/content/2021-12-02-toying-with-virtio/Makefile?h=main
-[dockerfile]: https://git.memzero.de/blog/tree/content/2021-12-02-toying-with-virtio/Dockerfile?h=main
-[initramfs]: https://www.kernel.org/doc/Documentation/filesystems/ramfs-rootfs-initramfs.txt
-[virtio]: http://docs.oasis-open.org/virtio/virtio/v1.1/virtio-v1.1.pdf
-[qemu-nic-opts]: https://www.qemu.org/docs/master/system/invocation.html#hxtool-5
-[qemu-user-net]: https://www.qemu.org/docs/master/system/devices/net.html#using-the-user-mode-network-stack
-[libslirp]: https://gitlab.com/qemu-project/libslirp
-[osi-2]: https://osi-model.com/data-link-layer
-[osi-4]: https://osi-model.com/transport-layer
diff --git a/content/2021-12-02-toying-with-virtio/index.md b/content/2021-12-02-toying-with-virtio/index.md
new file mode 100644
index 0000000..c2ff031
--- /dev/null
+++ b/content/2021-12-02-toying-with-virtio/index.md
@@ -0,0 +1,373 @@
++++
+title = "QEMU virtio configurations"
+
+[taxonomies]
+tags = ["linux", "qemu", "virtio"]
++++
+
+For my own reference I wanted to document some minimal [`virtio`][virtio]
+device configurations with qemu and the required Linux kernel configuration to
+enable those devices.
+
+The devices we will use are `virtio console`, `virtio blk` and `virtio net`.
+
+To make use of the virtio devices in qemu we are going to build and boot into
+busybox based [`initramfs`][initramfs].
+
+## Build initramfs
+
+For the initramfs there is not much magic, we will grab a copy of busybox,
+configure it with the default config (`defconfig`) and enable static linking as
+we will use it as rootfs.
+
+For the `init` process we will use the one provided by busybox but we have to
+symlink it to `/init` as during boot, the kernel will extract the cpio
+compressed initramfs into `rootfs` and look for the `/init` file. If that's not
+found the kernel will fallback to an older mechanism an try to mount a root
+partition (which we don't have).
+> Optionally the init binary could be specified with the `rdinit=` kernel boot
+> parameter.
+
+We populate the `/etc/inittab` and `/etc/init.d/rcS` with a minimal
+configuration to mount the `proc`, `sys` and `dev` filesystems and drop into a
+shell after the boot is completed. \
+Additionally we setup `/etc/passwd` and `/etc/shadow` with an entry for the
+`root` user with the password `1234`, so we can login via the virtio console
+later.
+
+```sh
+{{ include_range(path="content/2021-12-02-toying-with-virtio/build_initramfs.sh", start=31, end=67) }}
+```
+
+The full build script is available under [build_initramfs.sh][build-initramfs].
+
+## Virtio console
+
+To enable support for the virtio console we enable the kernel configs shown
+below.
+The pci configurations are enabled because in qemu the virtio console front-end
+device (the one presented to the guest) is attached to the pci bus.
+
+```sh
+{{ include_range(path="content/2021-12-02-toying-with-virtio/build_kernel.sh", start=32, end=38) }}
+```
+
+The full build script is available under [build_kernel.sh][build-kernel].
+
+To boot-up the guest we use the following qemu configuration.
+
+```sh
+qemu-system-x86_64                                            \
+  -nographic                                                  \
+  -cpu host                                                   \
+  -enable-kvm                                                 \
+  -kernel ./linux-$(VER)/arch/x86/boot/bzImage                \
+  -append "earlyprintk=ttyS0 console=ttyS0 root=/dev/ram0 ro" \
+  -initrd ./initramfs.cpio.gz                                 \
+  -device virtio-serial-pci                                   \
+  -device virtconsole,chardev=vcon,name=console.0             \
+  -chardev socket,id=vcon,ipv4=on,host=localhost,port=2222,server,telnet=on,wait=off
+```
+
+The important parts in this configuration are the last three lines.
+
+The `virtio-serial-pci` device creates the serial bus where the virtio console
+is attached to.
+
+The `virtconsole` creates the virtio console device exposed to the guest
+(front-end). The `chardev=vcon` option specifies that the chardev with
+`id=vcon` is attached as back-end to the virtio console.
+The back-end device is the one we will have access to from the host running the
+emulation.
+
+The chardev back-end we configure to be a `socket`, running a telnet server
+listening on port 2222. The `wait=off` tells qemu that it can directly boot
+without waiting for a client connection.
+
+After booting the guest we are dropped into a shell and can verify that our
+device is being detected properly.
+```sh
+root@virtio-box ~ # ls /sys/bus/virtio/devices/
+virtio0
+root@virtio-box ~ # cat /sys/bus/virtio/devices/virtio0/virtio-ports/vport0p0/name
+console.0
+```
+
+In `/etc/inittab`, we already configured to spawn `getty` on the first
+hypervisor console `/dev/hvc0`. This will effectively run `login(1)` over the
+serial console.
+
+From the host we can run `telnet localhost 2222` and are presented with a login shell to the guest.
+
+As we already included to launch `getty` on the first hypervisor console
+`/dev/hvc0` in `/etc/inittab`, we can directly connect to the back-end chardev
+and login to the guest with `root:1234`.
+
+```sh
+> telnet -4 localhost 2222
+Trying 127.0.0.1...
+Connected to localhost.
+Escape character is '^]'.
+
+virtio-box login: root
+Password:
+root@virtio-box ~ #
+```
+
+## Virtio blk
+
+To enable support for the virtio block device we enable the kernel configs
+shown below.
+First we enable general support for block devices and then for virtio block
+devices. Additionally we enable support for the `ext2` filesystem because we
+are creating an ext2 filesystem to back the virtio block device.
+
+```sh
+{{ include_range(path="content/2021-12-02-toying-with-virtio/build_kernel.sh", start=40, end=47) }}
+```
+
+The full build script is available under [build_kernel.sh][build-kernel].
+
+Next we are creating the ext2 filesystem image. This we'll do by creating an
+`128M` blob and format it with ext2 afterwards. Then we can mount the image
+via a `loop` device and populate the filesystem.
+```sh
+{{ include_range(path="content/2021-12-02-toying-with-virtio/build_ext2.sh", start=3, end=7) }}
+```
+
+Before booting the guest we will attach the virtio block device to the VM.
+Therefore we add the `-drive` configuration to our previous qemu invocation.
+
+```sh
+qemu-system-x86_64 \
+  ...
+  -drive if=virtio,file=fs.ext2,format=raw
+```
+
+The `-drive` option is a shortcut for a `-device (front-end) / -blockdev
+(back-end)` pair.
+
+The `if=virtio` flag specifies the interface of the front-end device to be
+`virtio`.
+
+The `file` and `format` flags configure the back-end to be a disk image.
+
+After booting the guest we are dropped into a shell and can verify a few
+things. First we check if the virtio block device is detected, then we check if
+we have support for the ext2 filesystem and finally we mount the disk.
+
+```sh
+root@virtio-box ~ # ls -l /sys/block/
+lrwxrwxrwx 1 root 0 0 Dec  3 22:46 vda -> ../devices/pci0000:00/0000:00:05.0/virtio1/block/vda
+
+root@virtio-box ~ # cat /proc/filesystems
+...
+       ext2
+
+root@virtio-box ~ # mount -t ext2 /dev/vda /mnt
+EXT2-fs (vda): warning: mounting unchecked fs, running e2fsck is recommended
+ext2 filesystem being mounted at /mnt supports timestamps until 2038 (0x7fffffff)
+
+root@virtio-box ~ # cat /mnt/hello
+world
+```
+
+## Virtio net
+
+To enable support for the virtio network device we enable the kernel configs
+shown below.
+First we enable general support for networking and TCP/IP and then enable the
+core networking driver and the virtio net driver.
+
+```sh
+{{ include_range(path="content/2021-12-02-toying-with-virtio/build_kernel.sh", start=49, end=62) }}
+```
+
+The full build script is available under [build_kernel.sh][build-kernel].
+
+For the qemu device emulation we already decided on the front-end device, which
+will be our virtio net device. \
+On the back-end we will choose the [`user`][qemu-user-net] option. This enables
+a network stack implemented in userspace based on [libslirp][libslirp], which
+has the benefit that we do not need to setup additional network interfaces and
+therefore require any privileges. Fundamentally, [libslirp][libslirp] works by
+replaying [Layer 2][osi-2] packets received from the guest NIC via the socket
+API on the host ([Layer 4][osi-4]) and vice versa. User networking comes with a
+set of limitations, for example
+- Can not use `ping` inside the guest as `ICMP` is not supported.
+- The guest is not accessible from the host.
+
+With the guest, qemu and the host in the picture this looks something like the
+following.
+```
++--------------------------------------------+
+|                                       host |
+|     +-------------------------+            |
+|     | guest                   |            |
+|     |                         |            |
+|     |                    user |            |
+|     +------+------+-----------+            |
+|     |      | eth0 |    kernel |            |
+|     |      +--+---+           |            |
+|     |         |               |            |
+|     |   +-----v--------+      |            |
+|     |   | nic (virtio) |      |            |
+|  +--+---+-----+--------+------+--+         |
+|  |            | Layer 2     qemu |         |
+|  |            | (eth frames)     |         |
+|  |       +----v-----+            |         |
+|  |       | libslirp |            |         |
+|  |       +----+-----+            |         |
+|  |            | Layer 4          |         |
+|  |            | (socket API)     |    user |
++--+---------+--v---+--------------+---------+
+|            | eth0 |                 kernel |
+|            +------+                        |
++--------------------------------------------+
+```
+
+The user networking implements a virtually NAT'ed sub-network with the address
+range `10.0.2.0/24` running an internal dhcp server. By default, the dhcp
+server assigns the following IP addresses which are interesting to us:
+- `10.0.2.2` host running the qemu emulation
+- `10.0.2.3` virtual DNS server
+> The netdev options `net=addr/mask`, `host=addr`, `dns=addr` can be used to
+> re-configure the sub-network (see [network options][qemu-nic-opts]).
+
+With the details of the sub-network in mind we can add some additional setup to
+the initramfs which performs the basic network setup.
+
+We add the virtual DNS server to `/etc/resolv.conf` which will be used by the
+libc resolver functions.
+
+Additionally we assign a static ip to the `eth0` network interface, bring the
+interface up and define the default route via the host `10.0.2.2`.
+
+```sh
+{{ include_range(path="content/2021-12-02-toying-with-virtio/build_initramfs.sh", start=69, end=85) }}
+```
+
+The full build script is available under [build_initramfs.sh][build-initramfs].
+
+Before booting the guest we will attach the virtio net device and configure to
+use the user network stack.
+Therefore we add the `-nic` configuration to our previous qemu invocation.
+
+```sh
+qemu-system-x86_64 \
+  ...
+  -nic user,model=virtio-net-pci
+```
+
+The `-nic` option is a shortcut for a `-device (front-end) / -netdev
+(back-end)` pair.
+
+After booting the guest we are dropped into a shell and can verify a few
+things. First we check if the virtio net device is detected. Then we check if
+the interface got configured and brought up correctly.
+
+```sh
+root@virtio-box ~ # ls -l /sys/class/net/
+lrwxrwxrwx 1 root 0 0 Dec  4 16:56 eth0 -> ../../devices/pci0000:00/0000:00:03.0/virtio0/net/eth0
+lrwxrwxrwx 1 root 0 0 Dec  4 16:56 lo -> ../../devices/virtual/net/lo
+
+
+root@virtio-box ~ # ip -o a
+2: eth0    inet 10.0.2.15/24 scope global eth0  ...
+
+root@virtio-box ~ # ip route
+default via 10.0.2.2 dev eth0
+10.0.2.0/24 dev eth0 scope link  src 10.0.2.15
+```
+
+We can resolve out domain and see that the virtual DNS gets contacted.
+
+```sh
+root@virtio-box ~ # nslookup memzero.de
+Server:   10.0.2.3
+Address:  10.0.2.3:53
+
+Non-authoritative answer:
+Name:    memzero.de
+Address: 46.101.148.203
+```
+
+Additionally we can try to access a service running on the host. Therefore we
+run a simple http server on the host (where we launched qemu) with the
+following command `python3 -m http.server --bind 0.0.0.0 1234`. This will
+launch the server to listen for any incoming address at port `1234`.
+
+From within the guest we can manually craft a simple http `GET` request and
+send it to the http server running on the host. For that we use the IP address
+`10.0.2.2` which the dhcp assigned to our host.
+
+```sh
+root@virtio-box ~ # echo "GET / HTTP/1.0" | nc 10.0.2.2 1234
+HTTP/1.0 200 OK
+Server: SimpleHTTP/0.6 Python/3.9.7
+Date: Sat, 04 Dec 2021 16:58:56 GMT
+Content-type: text/html; charset=utf-8
+Content-Length: 917
+
+<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
+<title>Directory listing for /</title>
+</head>
+<body>
+<h1>Directory listing for /</h1>
+<hr>
+<ul>
+<li><a href="build_initramfs.sh">build_initramfs.sh</a></li>
+...
+</ul>
+<hr>
+</body>
+</html>
+```
+
+## Appendix: Workspace
+
+To re-produce the setup and play around with it just grab a copy of the
+following files:
+- [Dockerfile][dockerfile]
+- [Makefile][makefile]
+- [build_initramfs.sh][build-initramfs]
+- [build_kernel.sh][build-kernel]
+- [build_ext2.sh][build-ext2]
+
+Then run the following steps to build everything. The prefix `[H]` and `[C]`
+indicate whether this command is run on the host or inside the container
+respectively.
+```sh
+# To see all the make targets.
+[H] make help
+
+# Build docker image, start a container with the current working dir
+# mounted. On the first invocation this takes some minutes to build
+# the image.
+[H]: make docker
+
+# Build kernel and initramfs.
+[C]: make
+
+# Build ext2 fs as virtio blkdev backend.
+[H]: make ext2
+
+# Start qemu guest.
+[H]: make run
+```
+
+[build-initramfs]: https://git.memzero.de/blog/tree/content/2021-12-02-toying-with-virtio/build_initramfs.sh?h=main
+[build-kernel]: https://git.memzero.de/blog/tree/content/2021-12-02-toying-with-virtio/build_kernel.sh?h=main
+[build-ext2]: https://git.memzero.de/blog/tree/content/2021-12-02-toying-with-virtio/build_ext2.sh?h=main
+[makefile]: https://git.memzero.de/blog/tree/content/2021-12-02-toying-with-virtio/Makefile?h=main
+[dockerfile]: https://git.memzero.de/blog/tree/content/2021-12-02-toying-with-virtio/Dockerfile?h=main
+[initramfs]: https://www.kernel.org/doc/Documentation/filesystems/ramfs-rootfs-initramfs.txt
+[virtio]: http://docs.oasis-open.org/virtio/virtio/v1.1/virtio-v1.1.pdf
+[qemu-nic-opts]: https://www.qemu.org/docs/master/system/invocation.html#hxtool-5
+[qemu-user-net]: https://www.qemu.org/docs/master/system/devices/net.html#using-the-user-mode-network-stack
+[libslirp]: https://gitlab.com/qemu-project/libslirp
+[osi-2]: https://osi-model.com/data-link-layer
+[osi-4]: https://osi-model.com/transport-layer
diff --git a/content/2022-06-18-libclang-c-to-llvm-ir.md b/content/2022-06-18-libclang-c-to-llvm-ir.md
deleted file mode 100644
index 7d3ee63..0000000
--- a/content/2022-06-18-libclang-c-to-llvm-ir.md
+++ /dev/null
@@ -1,32 +0,0 @@
-+++
-title = "C to LLVM IR in memory using libclang"
-
-[taxonomies]
-tags = ["llvm", "clang", "c++"]
-+++
-
-For some experiments with the LLVM just in time (JIT) APIs, I was looking for a
-way to compile in memory from `C -> LLVM IR` and without invoking Clang as a
-child process.
-
-I created a minimal example for my purpose based on the [Clang
-source][src-clang] code and the example given in the blog post [Compiling C++
-Code In Memory With Clang][blog-clang-in-memory].
-
-The code listing below shows the example with detailed comments inlined, hence
-I am not further describing any details here.
-
-> The example was build & tested with LLVM & Clang 13.
-
-```cpp
-{{ include(path="content/2022-06-18-libclang-c-to-llvm-ir/gen-ir.cc") }}
-```
-
-The following Makefile can be used to compile and run the example.
-
-```make
-{{ include(path="content/2022-06-18-libclang-c-to-llvm-ir/Makefile") }}
-```
-
-[src-clang]: https://github.com/llvm/llvm-project/tree/main/clang
-[blog-clang-in-memory]: https://blog.audio-tk.com/2018/09/18/compiling-c-code-in-memory-with-clang/
diff --git a/content/2022-06-18-libclang-c-to-llvm-ir/index.md b/content/2022-06-18-libclang-c-to-llvm-ir/index.md
new file mode 100644
index 0000000..7d3ee63
--- /dev/null
+++ b/content/2022-06-18-libclang-c-to-llvm-ir/index.md
@@ -0,0 +1,32 @@
++++
+title = "C to LLVM IR in memory using libclang"
+
+[taxonomies]
+tags = ["llvm", "clang", "c++"]
++++
+
+For some experiments with the LLVM just in time (JIT) APIs, I was looking for a
+way to compile in memory from `C -> LLVM IR` and without invoking Clang as a
+child process.
+
+I created a minimal example for my purpose based on the [Clang
+source][src-clang] code and the example given in the blog post [Compiling C++
+Code In Memory With Clang][blog-clang-in-memory].
+
+The code listing below shows the example with detailed comments inlined, hence
+I am not further describing any details here.
+
+> The example was build & tested with LLVM & Clang 13.
+
+```cpp
+{{ include(path="content/2022-06-18-libclang-c-to-llvm-ir/gen-ir.cc") }}
+```
+
+The following Makefile can be used to compile and run the example.
+
+```make
+{{ include(path="content/2022-06-18-libclang-c-to-llvm-ir/Makefile") }}
+```
+
+[src-clang]: https://github.com/llvm/llvm-project/tree/main/clang
+[blog-clang-in-memory]: https://blog.audio-tk.com/2018/09/18/compiling-c-code-in-memory-with-clang/
diff --git a/content/2022-07-07-llvm-orc-jit.md b/content/2022-07-07-llvm-orc-jit.md
deleted file mode 100644
index 6868518..0000000
--- a/content/2022-07-07-llvm-orc-jit.md
+++ /dev/null
@@ -1,42 +0,0 @@
-+++
-title = "Jit C in memory using LLVM ORC api"
-
-[taxonomies]
-tags = ["llvm", "clang", "c++"]
-+++
-
-Based on the in-memory compiler shared in the last post ([C to LLVM IR in
-memory using libclang](@/2022-06-18-libclang-c-to-llvm-ir.md)), this post
-demonstrates a small *just in time (JIT)* compiler which allows to compile C
-code to host native code in-memory.
-
-The JIT compiler is based on the LLVM [ORCv2 API][llvm-orc2] (the newest LLVM
-JIT API at the time of writing) and the crucial parts are taken from the [JIT
-tutorial][llvm-jit-tut].
-
-The sources are available under [llvm-orc-jit][post-src].
-
-### main.cc
-```cpp
-{{ include(path="content/2022-07-07-llvm-orc-jit/main.cc") }}
-```
-
-### jit.h
-```cpp
-{{ include(path="content/2022-07-07-llvm-orc-jit/jit.h") }}
-```
-
-### compiler.h
-```cpp
-{{ include(path="content/2022-07-07-llvm-orc-jit/ccompiler.h") }}
-```
-
-### Makefile
-```make
-{{ include(path="content/2022-07-07-llvm-orc-jit/Makefile") }}
-```
-[post-src]: https://git.memzero.de/blog/tree/content/2022-07-07-llvm-orc-jit?h=main
-[src-clang]: https://github.com/llvm/llvm-project/tree/main/clang
-[blog-clang-in-memory]: https://blog.audio-tk.com/2018/09/18/compiling-c-code-in-memory-with-clang/
-[llvm-jit-tut]: https://www.llvm.org/docs/tutorial/BuildingAJIT1.html
-[llvm-orc2]: https://www.llvm.org/docs/ORCv2.html
diff --git a/content/2022-07-07-llvm-orc-jit/index.md b/content/2022-07-07-llvm-orc-jit/index.md
new file mode 100644
index 0000000..4b2add0
--- /dev/null
+++ b/content/2022-07-07-llvm-orc-jit/index.md
@@ -0,0 +1,42 @@
++++
+title = "Jit C in memory using LLVM ORC api"
+
+[taxonomies]
+tags = ["llvm", "clang", "c++"]
++++
+
+Based on the in-memory compiler shared in the last post ([C to LLVM IR in
+memory using libclang](@/2022-06-18-libclang-c-to-llvm-ir/index.md)), this post
+demonstrates a small *just in time (JIT)* compiler which allows to compile C
+code to host native code in-memory.
+
+The JIT compiler is based on the LLVM [ORCv2 API][llvm-orc2] (the newest LLVM
+JIT API at the time of writing) and the crucial parts are taken from the [JIT
+tutorial][llvm-jit-tut].
+
+The sources are available under [llvm-orc-jit][post-src].
+
+### main.cc
+```cpp
+{{ include(path="content/2022-07-07-llvm-orc-jit/main.cc") }}
+```
+
+### jit.h
+```cpp
+{{ include(path="content/2022-07-07-llvm-orc-jit/jit.h") }}
+```
+
+### compiler.h
+```cpp
+{{ include(path="content/2022-07-07-llvm-orc-jit/ccompiler.h") }}
+```
+
+### Makefile
+```make
+{{ include(path="content/2022-07-07-llvm-orc-jit/Makefile") }}
+```
+[post-src]: https://git.memzero.de/blog/tree/content/2022-07-07-llvm-orc-jit?h=main
+[src-clang]: https://github.com/llvm/llvm-project/tree/main/clang
+[blog-clang-in-memory]: https://blog.audio-tk.com/2018/09/18/compiling-c-code-in-memory-with-clang/
+[llvm-jit-tut]: https://www.llvm.org/docs/tutorial/BuildingAJIT1.html
+[llvm-orc2]: https://www.llvm.org/docs/ORCv2.html
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