gdb how to set breakpoint in dynamic library opened by dlopen

Question

Afternoon,everbody. I have an application 'test' compiled by main.c . A dynamic liabrary 'libtest.so' which is compiled by test.cpp with '-g'. In main.c I invoke the 'libtest.so' with 'dlopen' . And now I want to set a breakpoint in test.cpp ,but the gdb never hit it. I do as follow:

gdb ./test -d /home/lcl/test

break test.cpp:35

run

can anybody give me some tips ,thanks!

thanks to reply me , -d just to point the directory gdb search for. just like dir command — Wayne.liu, Apr 04 '14 at 10:00
I tried it. line number 35 just a function name. if I compile test.c with 'gcc -c main.c -o test -ltest -L./' I can set breakpoint but failed when open with dlopen ... — Wayne.liu, Apr 04 '14 at 10:16
yeah, but now I must have supper. I will attach the code later. and thanks Mantosh Kumar — Wayne.liu, Apr 04 '14 at 10:22
Yes, with this little progress you got eligibility to have supper. :) — user207064, Apr 04 '14 at 10:28
I actually have the same problem 2 years later, how did you figure this out ? — xchg.ca, Feb 12 '16 at 18:21

score 3 · Answer 1 · answered Apr 05 '14 at 05:53

You should first verify that dlopen is actually succeeding (it's likely that it's not).

To do so:

set a breakpoint in main.c after dlopen.
confirm that returned handle is not NULL

At that point, GDB should have loaded symbols for libtest.so, and libtest.so should show up in info shared GDB output.

If everything looks good, info break should show an active breakpoint in test.cpp:35 at some address. If that breakpoint is never hit, it's likely that you never actually exercise that line of code.

gdb how to set breakpoint in dynamic library opened by dlopen

1 Answers1