practice
Tool gdb: The GNU Project Debugger. This is the user manual.
# Start target executable app running under GDB control
gdb [--args] <target_app> [args list]
# attach to a running process
gdb -p <pid>
# we can set break points
break <line_idendifier>
# Use the run command to start your program under GDB.
r
# we can step to the next line
n
# or next step
s
# or continue
c
# print var values that show up during the step execution.
p <var_name>
# quit after done
quit
Use the pytorch segmentation fault as an example:
python -c "import torch; print(torch)"
# segmentation fault (core dumped)
gdb python
# option -c: use content/file as a core dump to examine.
r -c "import torch; print(torch)"
# backtrace
bt
#0 0x0000000000002360 in ?? ()
#1 0x00007ffff7de5a6a in call_init (l=<optimized out>, argc=argc@entry=3,
argv=argv@entry=0x7fffffffde28, env=env@entry=0xb85860) at dl-init.c:72
#2 0x00007ffff7de5b7b in call_init (env=0xb85860, argv=0x7fffffffde28,
argc=3, l=<optimized out>) at dl-init.c:30
#3 _dl_init (main_map=main_map@entry=0xeb4270, argc=3, argv=0x7fffffffde28,
env=0xb85860) at dl-init.c:120
#4 0x00007ffff7deab86 in dl_open_worker (a=a@entry=0x7fffffffb840)
at dl-open.c:575
#5 0x00007ffff6d88d64 in __GI__dl_catch_error (objname=0x7fffffffb830,
errstring=0x7fffffffb838, mallocedp=0x7fffffffb82f,
operate=0x7ffff7dea7a0 <dl_open_worker>, args=0x7fffffffb840)
at dl-error-skeleton.c:198
#6 0x00007ffff7dea0d9 in _dl_open (
file=0x7fffdf813a60 "/usr/local/lib/python3.6/dist-packages/torch/_C.cpython-36m-x86_64-linux-gnu.so", mode=-2147483391,
caller_dlopen=0x58de76 <_PyImport_FindSharedFuncptr+390>, nsid=-2,
argc=<optimized out>, argv=<optimized out>, env=0xb85860) at dl-open.c:660
#7 0x00007ffff79b2ff6 in dlopen_doit (a=a@entry=0x7fffffffba50) at dlopen.c:66
#8 0x00007ffff6d88d64 in __GI__dl_catch_error (objname=0xb85d10,
errstring=0xb85d18, mallocedp=0xb85d08,
operate=0x7ffff79b2fa0 <dlopen_doit>, args=0x7fffffffba50)
at dl-error-skeleton.c:198
#9 0x00007ffff79b3759 in _dlerror_run (
operate=operate@entry=0x7ffff79b2fa0 <dlopen_doit>,
args=args@entry=0x7fffffffba50) at dlerror.c:163
#10 0x00007ffff79b3092 in __dlopen (file=<optimized out>, mode=<optimized out>)
at dlopen.c:87
#11 0x000000000058de76 in _PyImport_FindSharedFuncptr ()
#12 0x0000000000576b18 in _PyImport_LoadDynamicModuleWithSpec ()
#13 0x00000000005743c5 in ?? ()
#14 0x00000000004c47ed in PyCFunction_Call ()
#15 0x0000000000557040 in _PyEval_EvalFrameDefault ()
#16 0x000000000054efc1 in ?? ()
#17 0x000000000054f24d in ?? ()
#18 0x0000000000553aaf in _PyEval_EvalFrameDefault ()
#19 0x000000000054e4c8 in ?? ()
#20 0x000000000054f4f6 in ?? ()
#21 0x0000000000553aaf in _PyEval_EvalFrameDefault ()
#22 0x000000000054e4c8 in ?? ()
#23 0x000000000054f4f6 in ?? ()
#24 0x0000000000553aaf in _PyEval_EvalFrameDefault ()
#25 0x000000000054e4c8 in ?? ()
#26 0x000000000054f4f6 in ?? ()
#27 0x0000000000553aaf in _PyEval_EvalFrameDefault ()
#28 0x000000000054e4c8 in ?? ()
#29 0x000000000054f4f6 in ?? ()
#30 0x0000000000553aaf in _PyEval_EvalFrameDefault ()
#31 0x000000000054e4c8 in ?? ()
#32 0x00000000005582c2 in _PyFunction_FastCallDict ()
#33 0x0000000000459981 in _PyObject_FastCallDict ()
#34 0x000000000045b034 in _PyObject_CallMethodIdObjArgs ()
#35 0x000000000057581a in PyImport_ImportModuleLevelObject ()
#36 0x0000000000556add in _PyEval_EvalFrameDefault ()
#37 0x000000000054efc1 in ?? ()
#38 0x000000000054ff73 in PyEval_EvalCode ()
#39 0x000000000054cfda in ?? ()
#40 0x00000000004c47ed in PyCFunction_Call ()
#41 0x0000000000557040 in _PyEval_EvalFrameDefault ()
#42 0x000000000054efc1 in ?? ()
#43 0x000000000054f24d in ?? ()
#44 0x0000000000553aaf in _PyEval_EvalFrameDefault ()
#45 0x000000000054e4c8 in ?? ()
#46 0x000000000054f4f6 in ?? ()
#47 0x0000000000553aaf in _PyEval_EvalFrameDefault ()
#48 0x000000000054e4c8 in ?? ()
#49 0x000000000054f4f6 in ?? ()
#50 0x0000000000553aaf in _PyEval_EvalFrameDefault ()
#51 0x000000000054e4c8 in ?? ()
#52 0x000000000054f4f6 in ?? ()
#53 0x0000000000553aaf in _PyEval_EvalFrameDefault ()
#54 0x000000000054e4c8 in ?? ()
#55 0x00000000005582c2 in _PyFunction_FastCallDict ()
#56 0x0000000000459981 in _PyObject_FastCallDict ()
#57 0x000000000045b034 in _PyObject_CallMethodIdObjArgs ()
#58 0x000000000057581a in PyImport_ImportModuleLevelObject ()
#59 0x0000000000556add in _PyEval_EvalFrameDefault ()
#60 0x000000000054efc1 in ?? ()
#61 0x000000000054ff73 in PyEval_EvalCode ()
#62 0x000000000042c37a in PyRun_SimpleStringFlags ()
#63 0x0000000000441178 in Py_Main ()
#64 0x0000000000421f64 in main ()
Tool ldd: print shared library dependencies.
ldd /usr/local/lib/python3.6/dist-packages/torch/_C.cpython-36m-x86_64-linux-gnu.so
# linux-vdso.so.1 => (0x00007ffcce1f5000)
# libshm.so => /usr/local/lib/python3.6/dist-packages/torch/lib/libshm.so (0x00007f37cdcac000)
# libcudart.so.9.0 => /usr/local/lib/python3.6/dist-packages/torch/lib/libcudart.so.9.0 (0x00007f37cda3d000)
# libnvToolsExt.so.1 => /usr/local/lib/python3.6/dist-packages/torch/lib/libnvToolsExt.so.1 (0x00007f37cd833000)
# libcudnn.so.7 => /usr/local/lib/python3.6/dist-packages/torch/lib/libcudnn.so.7 (0x00007f37bc5c0000)
# libTH.so.1 => /usr/local/lib/python3.6/dist-packages/torch/lib/libTH.so.1 (0x00007f37b9a91000)
# libTHS.so.1 => /usr/local/lib/python3.6/dist-packages/torch/lib/libTHS.so.1 (0x00007f37b9860000)
# libTHNN.so.1 => /usr/local/lib/python3.6/dist-packages/torch/lib/libTHNN.so.1 (0x00007f37b951d000)
# libATen.so.1 => /usr/local/lib/python3.6/dist-packages/torch/lib/libATen.so.1 (0x00007f37b8d0f000)
# libTHC.so.1 => /usr/local/lib/python3.6/dist-packages/torch/lib/libTHC.so.1 (0x00007f37a4353000)
# libTHCS.so.1 => /usr/local/lib/python3.6/dist-packages/torch/lib/libTHCS.so.1 (0x00007f37a3fc3000)
# libTHCUNN.so.1 => /usr/local/lib/python3.6/dist-packages/torch/lib/libTHCUNN.so.1 (0x00007f379e8ef000)
# libnccl.so.1 => /usr/local/lib/python3.6/dist-packages/torch/lib/libnccl.so.1 (0x00007f379be65000)
# libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f379bc4e000)
# libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f379ba2f000)
# libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f379b64f000)
# /lib64/ld-linux-x86-64.so.2 (0x00007f37cf854000)
# librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007f379b447000)
# libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f379b0f1000)
# libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f379aeed000)
# libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f379ab65000)
# libgomp.so.1 => /usr/local/lib/python3.6/dist-packages/torch/lib/libgomp.so.1 (0x00007f379a94e000)
# libcublas.so.9.0 => /usr/local/lib/python3.6/dist-packages/torch/lib/libcublas.so.9.0 (0x00007f3797515000)
# libcurand.so.9.0 => /usr/local/lib/python3.6/dist-packages/torch/lib/libcurand.so.9.0 (0x00007f37935b0000)
# libcusparse.so.9.0 => /usr/local/lib/python3.6/dist-packages/torch/lib/libcusparse.so.9.0 (0x00007f378fe45000)
Reference: How do I list the symbols in a .so file
Using GNU nm:
nm -gD yourLib.so
# Add the "-C" option to see symbols of a C++ library
nm -gDC yourLib.so
If your .so file is in elf format, you have two options:
Either objdump (-C is also useful for demangling C++):
objdump -TC libz.so
libz.so: file format elf64-x86-64
DYNAMIC SYMBOL TABLE:
0000000000002010 l d .init 0000000000000000 .init
0000000000000000 DF *UND* 0000000000000000 GLIBC_2.2.5 free
0000000000000000 DF *UND* 0000000000000000 GLIBC_2.2.5 __errno_location
0000000000000000 w D *UND* 0000000000000000 _ITM_deregisterTMCloneTable
or use readelf:
readelf -Ws libz.so
Symbol table '.dynsym' contains 112 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
1: 0000000000002010 0 SECTION LOCAL DEFAULT 10
2: 0000000000000000 0 FUNC GLOBAL DEFAULT UND free@GLIBC_2.2.5 (14)
3: 0000000000000000 0 FUNC GLOBAL DEFAULT UND __errno_location@GLIBC_2.2.5 (14)
4: 0000000000000000 0 NOTYPE WEAK DEFAULT UND _ITM_deregisterTMCloneTable