python

Builtins
Give the compiler a hint which branch is hot, so it can lay out the code diff --git a/development/glibc.html b/development/glibc.html index 7c42a20..b6c29d9 100644 --- a/development/glibc.html +++ b/development/glibc.html @@ -81,7 +81,7 @@
[make] (./make.md)
+ @@ -293,7 +293,7 @@ As we can see the offset from relocation at index 0 points to

+                    
                         
                     
                 
diff --git a/development/make.html b/development/make.html
index f64de16..3304ebd 100644
--- a/development/make.html
+++ b/development/make.html
@@ -81,7 +81,7 @@
 
         
             
-                Introduction
1. Tools
1.1. zsh
1.2. bash
1.3. fish
1.4. tmux
1.5. git
1.6. awk
1.7. emacs
1.8. gpg
1.9. gdb
1.10. radare2
1.11. qemu
2. Resource analysis & monitor
2.1. lsof
2.2. ss
2.3. pidstat
2.4. pgrep
2.5. pmap
2.6. pstack
3. Trace and Profile
3.1. strace
3.2. ltrace
3.3. perf
3.4. OProfile
3.5. time
4. Binary
4.1. od
4.2. xxd
4.3. readelf
4.4. objdump
4.5. nm
5. Development
5.1. c++filt
5.2. c++
5.3. glibc
5.4. gcc
5.5. make
5.6. ld.so
6. Arch
6.1. x86_64
6.2. arm64
6.3. armv7
+                Introduction
1. Tools
1.1. zsh
1.2. bash
1.3. fish
1.4. tmux
1.5. git
1.6. awk
1.7. emacs
1.8. gpg
1.9. gdb
1.10. radare2
1.11. qemu
1.12. pacman
2. Resource analysis & monitor
2.1. lsof
2.2. ss
2.3. pidstat
2.4. pgrep
2.5. pmap
2.6. pstack
3. Trace and Profile
3.1. strace
3.2. ltrace
3.3. perf
3.4. OProfile
3.5. time
4. Binary
4.1. od
4.2. xxd
4.3. readelf
4.4. objdump
4.5. nm
5. Development
5.1. c++filt
5.2. c++
5.3. glibc
5.4. gcc
5.5. make
5.6. ld.so
5.7. symbol versioning
5.8. python
6. Arch
6.1. x86_64
6.2. arm64
6.3. armv7
             
             
         
diff --git a/development/python.html b/development/python.html
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+++ b/development/python.html
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+
+    
+        
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+        python - Notes
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+            
+                Introduction
1. Tools
1.1. zsh
1.2. bash
1.3. fish
1.4. tmux
1.5. git
1.6. awk
1.7. emacs
1.8. gpg
1.9. gdb
1.10. radare2
1.11. qemu
1.12. pacman
2. Resource analysis & monitor
2.1. lsof
2.2. ss
2.3. pidstat
2.4. pgrep
2.5. pmap
2.6. pstack
3. Trace and Profile
3.1. strace
3.2. ltrace
3.3. perf
3.4. OProfile
3.5. time
4. Binary
4.1. od
4.2. xxd
4.3. readelf
4.4. objdump
4.5. nm
5. Development
5.1. c++filt
5.2. c++
5.3. glibc
5.4. gcc
5.5. make
5.6. ld.so
5.7. symbol versioning
5.8. python
6. Arch
6.1. x86_64
6.2. arm64
6.3. armv7
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+                        Notes
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+                        python
+Decorator [run]
+Some decorator examples with type annotation.
+from typing import Callable
+
+def log(f: Callable[[int], None]) -> Callable[[int], None]:
+    def inner(x: int):
+        print(f"log::inner f={f.__name__} x={x}")
+        f(x)
+    return inner
+
+@log
+def some_fn(x: int):
+    print(f"some_fn x={x}")
+
+
+def log_tag(tag: str) -> Callable[[Callable[[int], None]], Callable[[int], None]]:
+    def decorator(f: Callable[[int], None]) -> Callable[[int], None]:
+        def inner(x: int):
+            print(f"log_tag::inner f={f.__name__} tag={tag} x={x}")
+            f(x)
+        return inner
+    return decorator
+
+@log_tag("some_tag")
+def some_fn2(x: int):
+    print(f"some_fn2 x={x}")
+
+Walrus operator [run]
+Walrus operator := added since python 3.8.
+from typing import Optional
+
+# Example 1: if let statements
+
+def foo(ret: Optional[int]) -> Optional[int]:
+    return ret
+
+if r := foo(None):
+    print(f"foo(None) -> {r}")
+
+if r := foo(1337):
+    print(f"foo(1337) -> {r}")
+
+# Example 2: while let statements
+
+toks = iter(['a', 'b', 'c'])
+while tok := next(toks, None):
+    print(f"{tok}")
+
+# Example 3: list comprehension
+
+print([tok for t in ["  a", "  ", " b "] if (tok := t.strip())])
+
+Unittest [run]
+Run unittests directly from the command line as 

+python3 -m unittest -v test
+Optionally pass -k <patter> to only run subset of tests.
+# file: test.py
+
+import unittest
+
+class MyTest(unittest.TestCase):
+    def setUp(self):
+        pass
+    def tearDown(self):
+        pass
+    # Tests need to start with the prefix 'test'.
+    def test_foo(self):
+        self.assertEqual(1 + 2, 3)
+    def test_bar(self):
+        with self.assertRaises(IndexError):
+            list()[0]
+
+Doctest [run]
+Run doctests directly from the command line as 

+python -m doctest -v test.py
+# file: test.py
+
+def sum(a: int, b: int) -> int:
+    """Sum a and b.
+
+    >>> sum(1, 2)
+    3
+
+    >>> sum(10, 20)
+    30
+    """
+    return a + b
+
+timeit
+Micro benchmarking.
+python -m timeit '[x.strip() for x in ["a ", " b"]]'
+
+
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diff --git a/development/symbolver.html b/development/symbolver.html
new file mode 100644
index 0000000..bb8ac43
--- /dev/null
+++ b/development/symbolver.html
@@ -0,0 +1,427 @@
+
+
+    
+        
+        
+        symbol versioning - Notes
+        
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+        
+        
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+        
+        
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+        
+        
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+        
+        
+
+        
+            
+                Introduction
1. Tools
1.1. zsh
1.2. bash
1.3. fish
1.4. tmux
1.5. git
1.6. awk
1.7. emacs
1.8. gpg
1.9. gdb
1.10. radare2
1.11. qemu
1.12. pacman
2. Resource analysis & monitor
2.1. lsof
2.2. ss
2.3. pidstat
2.4. pgrep
2.5. pmap
2.6. pstack
3. Trace and Profile
3.1. strace
3.2. ltrace
3.3. perf
3.4. OProfile
3.5. time
4. Binary
4.1. od
4.2. xxd
4.3. readelf
4.4. objdump
4.5. nm
5. Development
5.1. c++filt
5.2. c++
5.3. glibc
5.4. gcc
5.5. make
5.6. ld.so
5.7. symbol versioning
5.8. python
6. Arch
6.1. x86_64
6.2. arm64
6.3. armv7
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+                        Notes
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+                        ELF Symbol Versioning
+The ELF symbol versioning mechanism allows to attach version
+information to symbols.
+This can be used to express symbol version requirements or to provide certain
+symbols multiple times in the same ELF file with different versions (eg for
+backwards compatibility).
+The libpthread.so library is an example which provides the
+pthread_cond_wait symbol multiple times but in different versions.
+With readelf the version of the symbol can be seen after the @.
+> readelf -W --dyn-syms /lib/libpthread.so
+
+Symbol table '.dynsym' contains 342 entries:
+   Num:    Value  Size Type    Bind   Vis      Ndx Name
+   ...
+   141: 0000f080   696 FUNC    GLOBAL DEFAULT   16 pthread_cond_wait@@GLIBC_2.3.2
+   142: 00010000   111 FUNC    GLOBAL DEFAULT   16 pthread_cond_wait@GLIBC_2.2.5
+
+The @@ denotes the default symbol version which will be used during
+static linking against the library.
+The following dump shows that the tmp program linked against lpthread will
+depend on the symbol version GLIBC_2.3.2, which is the default version.
+> echo "#include <pthread.h>
+        int main() {
+          return pthread_cond_wait(0,0);
+        }" | gcc -o tmp -xc - -lpthread;
+  readelf -W --dyn-syms tmp | grep pthread_cond_wait;
+
+Symbol table '.dynsym' contains 7 entries:
+   Num:    Value  Size Type    Bind   Vis      Ndx Name
+   ...
+     2: 00000000     0 FUNC    GLOBAL DEFAULT  UND pthread_cond_wait@GLIBC_2.3.2 (2)
+
+
+Only one symbol can be annotated as the @@ default version.
+
+Using the --version-info flag with readelf, more details on the symbol
+version info compiled into the tmp ELF file can be obtained.
+
+The .gnu.version section contains the version definition for each symbol in
+the .dynsym section. pthread_cond_wait is at index 2 in the .dynsym
+section, the corresponding symbol version is at index 2 in the
+.gnu.version section.
+The .gnu.version_r section contains symbol version requirements per shared
+library dependency (DT_NEEDED dynamic entry).
+
+> readelf -W --version-info --dyn-syms tmp
+
+Symbol table '.dynsym' contains 7 entries:
+   Num:    Value          Size Type    Bind   Vis      Ndx Name
+     0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT  UND 
+     1: 0000000000000000     0 NOTYPE  WEAK   DEFAULT  UND _ITM_deregisterTMCloneTable
+     2: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND pthread_cond_wait@GLIBC_2.3.2 (2)
+     3: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND __libc_start_main@GLIBC_2.2.5 (3)
+     4: 0000000000000000     0 NOTYPE  WEAK   DEFAULT  UND __gmon_start__
+     5: 0000000000000000     0 NOTYPE  WEAK   DEFAULT  UND _ITM_registerTMCloneTable
+     6: 0000000000000000     0 FUNC    WEAK   DEFAULT  UND __cxa_finalize@GLIBC_2.2.5 (3)
+
+Version symbols section '.gnu.version' contains 7 entries:
+ Addr: 0x0000000000000534  Offset: 0x000534  Link: 6 (.dynsym)
+  000:   0 (*local*)       0 (*local*)       2 (GLIBC_2.3.2)   3 (GLIBC_2.2.5)
+  004:   0 (*local*)       0 (*local*)       3 (GLIBC_2.2.5)
+
+Version needs section '.gnu.version_r' contains 2 entries:
+ Addr: 0x0000000000000548  Offset: 0x000548  Link: 7 (.dynstr)
+  000000: Version: 1  File: libc.so.6  Cnt: 1
+  0x0010:   Name: GLIBC_2.2.5  Flags: none  Version: 3
+  0x0020: Version: 1  File: libpthread.so.0  Cnt: 1
+  0x0030:   Name: GLIBC_2.3.2  Flags: none  Version: 2
+
+The gnu dynamic linker allows to inspect the version processing during runtime
+by setting the LD_DEBUG environment variable accordingly.
+# version: Display version dependencies.
+> LD_DEBUG=versions ./tmp
+    717904: checking for version `GLIBC_2.2.5' in file /usr/lib/libc.so.6 [0] required by file ./tmp [0]
+    717904: checking for version `GLIBC_2.3.2' in file /usr/lib/libpthread.so.0 [0] required by file ./tmp [0]
+    ...
+
+#  symbols : Display symbol table processing.
+#  bindings: Display information about symbol binding.
+> LD_DEBUG=symbols,bindings ./tmp
+    ...
+    718123: symbol=pthread_cond_wait;  lookup in file=./tmp [0]
+    718123: symbol=pthread_cond_wait;  lookup in file=/usr/lib/libpthread.so.0 [0]
+    718123: binding file ./tmp [0] to /usr/lib/libpthread.so.0 [0]: normal symbol `pthread_cond_wait' [GLIBC_2.3.2]
+
+Example: version script
+The following shows an example C++ library libfoo which provides the same
+symbol multiple times but in different versions.
+// file: libfoo.cc
+#include<stdio.h>
+
+// Bind function symbols to version nodes.
+//
+// ..@       -> Is the unversioned symbol.
+// ..@@..    -> Is the default symbol.
+
+__asm__(".symver func_v0,func@");
+__asm__(".symver func_v1,func@LIB_V1");
+__asm__(".symver func_v2,func@@LIB_V2");
+
+extern "C" {
+    void func_v0() { puts("func_v0"); }
+    void func_v1() { puts("func_v1"); }
+    void func_v2() { puts("func_v2"); }
+}
+
+__asm__(".symver _Z11func_cpp_v1i,_Z8func_cppi@LIB_V1");
+__asm__(".symver _Z11func_cpp_v2i,_Z8func_cppi@@LIB_V2");
+
+void func_cpp_v1(int) { puts("func_cpp_v1"); }
+void func_cpp_v2(int) { puts("func_cpp_v2"); }
+
+void func_cpp(int) { puts("func_cpp_v2"); }
+
+Version script for libfoo which defines which symbols for which versions are
+exported from the ELF file.
+# file: libfoo.ver
+LIB_V1 {
+    global:
+        func;
+        extern "C++" {
+            "func_cpp(int)";
+        };
+    local:
+        *;
+};
+
+LIB_V2 {
+    global:
+        func;
+        extern "C++" {
+            "func_cpp(int)";
+        };
+} LIB_V1;
+
+
+The local: section in LIB_V1 is a catch all, that matches any symbol
+not explicitly specified, and defines that the symbol is local and therefore
+not exported from the ELF file.
+
+The library libfoo can be linked with the version definitions in libfoo.ver
+by passing the version script to the linker with the --version-script flag.
+> g++ -shared -fPIC -o libfoo.so libfoo.cc -Wl,--version-script=libfoo.ver
+> readelf -W --dyn-syms libfoo.so | c++filt
+
+Symbol table '.dynsym' contains 14 entries:
+   Num:    Value          Size Type    Bind   Vis      Ndx Name
+   ...
+     6: 0000000000000000     0 OBJECT  GLOBAL DEFAULT  ABS LIB_V1
+     7: 000000000000114b    29 FUNC    GLOBAL DEFAULT   13 func_cpp(int)@LIB_V1
+     8: 0000000000001168    29 FUNC    GLOBAL DEFAULT   13 func_cpp(int)@@LIB_V2
+     9: 0000000000001185    29 FUNC    GLOBAL DEFAULT   13 func_cpp(int)@@LIB_V1
+    10: 0000000000000000     0 OBJECT  GLOBAL DEFAULT  ABS LIB_V2
+    11: 0000000000001109    22 FUNC    GLOBAL DEFAULT   13 func
+    12: 000000000000111f    22 FUNC    GLOBAL DEFAULT   13 func@LIB_V1
+    13: 0000000000001135    22 FUNC    GLOBAL DEFAULT   13 func@@LIB_V2
+
+The following program demonstrates how to make use of the different versions:
+// file: main.cc
+#include <dlfcn.h>
+#include <assert.h>
+
+// Links against default symbol in the lib.so.
+extern "C" void func();
+
+int main() {
+    // Call the default version.
+    func();
+
+#ifdef _GNU_SOURCE
+    typedef void (*fnptr)();
+
+    // Unversioned lookup.
+    fnptr fn_v0 = (fnptr)dlsym(RTLD_DEFAULT, "func");
+    // Version lookup.
+    fnptr fn_v1 = (fnptr)dlvsym(RTLD_DEFAULT, "func", "LIB_V1");
+    fnptr fn_v2 = (fnptr)dlvsym(RTLD_DEFAULT, "func", "LIB_V2");
+
+    assert(fn_v0 != 0);
+    assert(fn_v1 != 0);
+    assert(fn_v2 != 0);
+
+    fn_v0();
+    fn_v1();
+    fn_v2();
+#endif
+
+    return 0;
+}
+
+Compiling and running results in:
+> g++ -o main main.cc -ldl ./libfoo.so && ./main
+func_v2
+func_v0
+func_v1
+func_v2
+
+References
+
+ELF Symbol Versioning
+Binutils ld: Symbol Versioning
+LSB: Symbol Versioning
+How To Write Shared Libraries
+
+
+                    
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+    
+
-- 
cgit v1.2.3
Target options

Builtins

`__builtin_expect(expr, cond)`

Notes

Decorator [run]

Walrus operator [run]

Unittest [run]

Doctest [run]

timeit

Notes

ELF Symbol Versioning

Example: version script

References
