diff options
| -rw-r--r-- | Makefile | 10 | ||||
| -rw-r--r-- | README.me | 52 |
2 files changed, 57 insertions, 5 deletions
@@ -1,5 +1,8 @@ -all: $(patsubst example/%.c, out/%, $(wildcard example/*.c)) -all: $(patsubst example/%.c, run/%, $(wildcard example/*.c)) +libbt.so: bt.c + $(CC) -o $@ $^ -shared -fPIC -static-libgcc -ldl $(CFLAGS) + +run: $(patsubst example/%.c, out/%, $(wildcard example/*.c)) +run: $(patsubst example/%.c, run/%, $(wildcard example/*.c)) CFLAGS := -Wall -Wextra -g CFLAGS_recurse1 := -Wno-infinite-recursion @@ -12,9 +15,6 @@ out/%: example/%.c libbt.so @mkdir -p out $(CC) -o $@ $< -rdynamic $(CFLAGS) $(CFLAGS_$*) -libbt.so: bt.c - $(CC) -o $@ $^ -shared -fPIC -static-libgcc -ldl $(CFLAGS) - clean: $(RM) -r out $(RM) libbt.so diff --git a/README.me b/README.me new file mode 100644 index 0000000..f7122ca --- /dev/null +++ b/README.me @@ -0,0 +1,52 @@ +# preload-libbt + +`preload-libbt` is a utility library for some very special occasions. + +It aims to extract a backtrace when a program *segfaults*, on machines where +[`ptrace(2)`][ptrace] syscalls are restricted, and hence launching the program +under *gdb* or attaching wth *gdb* is not possible. + +The library must be `LD_PRELOAD`ed, which then installs a signal handler that +dumps a stacktrace. For it to work the program must adhere to the following +rules: + +- The program must not override the installed signal handler. +- If the program overrides the signal handler, it properly needs to implement +signal handler chaining. + +The preload library `libbt.so` is build with the default make target. +``` +make +``` + +The library installs *alternative signal stacks* to be able to do its work even +when the program *segfaults* due to a *stackoverflow*. This is demonstrated by +the `example/recurse*.c` examples. + +## Examples + +The following gives an example and shows how a stacktrace dump looks like. +``` +cc -o libbt.so bt.c -shared -fPIC -ldl +cc -o raise1 example/raise1.c -rdynamic +LD_PRELOAD=./libbt.so ./raise1 + +[INFO:BT]: installed signal handler +[INFO:BT]: caught signal 11 +# 0 [ 0x7f53b9e203f4] /usr/lib/libc.so.6+0x963f4 +# 1 [ 0x7f53b9dc7120] gsignal+0x20 /usr/lib/libc.so.6+0x3d100 +# 2 [ 0x55748166c147] foo+0xe raise1+0x1139 +# 3 [ 0x55748166c158] bar+0xe raise1+0x114a +# 4 [ 0x55748166c169] qux+0xe raise1+0x115b +# 5 [ 0x55748166c17a] main+0xe raise1+0x116c +# 6 [ 0x7f53b9dafe08] /usr/lib/libc.so.6+0x25e08 +# 7 [ 0x7f53b9dafecc] __libc_start_main+0x8c /usr/lib/libc.so.6+0x25e40 +# 8 [ 0x55748166c065] _start+0x25 raise1+0x1040 +``` + +Alternatively one can run `make run`, to run all examples under `example/`. + +## License +This project is licensed under the MIT license. + +[https://www.man7.org/linux/man-pages/man2/ptrace.2.html] |