GDB stepping into shared library shows "no such file" even though debug symbols are loaded

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I have a C library which is created with

cc -fPIC -g -O3   -c -o obj/my_lib.o my_lib.c
g++ -shared -Wl,-soname,libmy_lib.so.1  obj/my_lib.o -o libmy_lib.so.1.8.0

This library is packaged into debian packages with dpkg-buildpackage producing libmy_lib1-1.deb, libmy_lib1-dev-1.deb, and libmy_lib1-dbgsym-1.ddeb. Installing all of those packages, I can then compile/link a simple test program that calls into the library. This works. Running the test program works.

However, when I run GDB on the test program (on the same computer), I see

gdb$ break main
Breakpoint 1 at 0x87e: file test.c, line 10.
gdb$ info sharedlibrary
No shared libraries loaded at this time.
gdb$ r
Starting program: /tmp/a.out

Breakpoint 1, main () at test.c:10
10        my_library_func();
gdb$ info sharedlibrary
From                To                  Syms Read   Shared Object Library
0x00007ffff7dd5f10  0x00007ffff7df4b20  Yes         /lib64/ld-linux-x86-64.so.2
0x00007ffff7bac9a0  0x00007ffff7bad438  Yes         /usr/lib/x86_64-linux-gnu/libmy_lib.so.1
0x00007ffff74532d0  0x00007ffff75cbc3c  Yes         /lib/x86_64-linux-gnu/libc.so.6
0x00007ffff709fa80  0x00007ffff715e2f5  Yes         /lib/x86_64-linux-gnu/libm.so.6
0x00007ffff6e7eac0  0x00007ffff6e8f36d  Yes         /lib/x86_64-linux-gnu/libgcc_s.so.1
(*): Shared library is missing debugging information.
gdb$ s
my_library_func () at my_lib.c:299
299     my_lib.c: No such file or directory.

As you can see, GDB knows about the debug symbols for the library. However, it does not know about the source file for the library. How should I running GDB to it can resolve the C source code?

gdb shared-libraries c debugging
2 Answers

You need to also tell gdb where the source files are. Which means you also need the source files, not just the debugging symbols.

It's important that the sources you download are the actual ones used to compile the library, because debugging information only contains filename and line number. If you give gdb a file where the line numbers don't correspond (a different version, for example), the source lines printed by gdb will be very confusing. It has no way to know they are wrong. You should be able to use the src deb with the same version number as the library debs.

Once you have the source files, tell gdb where to look for them with

directory /path/to/source/files

You can specify several paths. Read help directory inside gdb.

Since you'll need to do this often, put that line into a gdbinit file. You'll probably want to use .gdbinit in your current directory, but .gdbinit in your home directory might also be a possibility. Gdb uses both.

If you're working with a library whose source is spread over a subdirectory tree, you might find it useful to set a substitution path:

set substitute-path /your/file/path /original/file/path

Again, more help is available with help set substitute-path.

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