Cannot Debug Shared Library - Symbols Not Loading Properly
I am currently writing a small library, and I want to check it for leaks (among other things); however, for some reason, gdb is not loading the library symbols. I have read many other posts on here (and various other places on the internet) about this, however, I cannot seem to find a solution. Here is what is going on:
I am compiling the shared library with the following flags (these are included in both the final shared library as well as all object files):
CFLAGS=-Wall -O0 -g -fPIC
Likewise, I am compiling the binary memtest (the client application for the library) to check for memory leaks and such with these flags
CFLAGS=-Wall -O0 -g
Now, I inserted a NULL pointer into the library to test if I could trace through it and "debug" the pointer (i.e. it's making it crash). So I try to run it through gdb, but it's a no go. The output of info sharedlibrary is the same for both the executable and the core:
(gdb) info sharedlibrary
From To Syms Read Shared Object Library
... Some libraries I am not worried about debugging...
0x00d37340 0x00d423a4 Yes (*) /home/raged/MyLIB/memtest/../lib/libMyLIB.so.0 <--- My lib
.... and some more....
(*): Shared library is missing debugging information.
As you can see, it's not loading the debug information. I am uncertain as to why this is. I have built and linked everything with the -g flag, and I even try -ggdb and -g3 but nothing seems to work properly. When I load in a core dump, this is what I see:
...some libs...
Reading symbols from /home/raged/MyLIB/memtest/../lib/libMyLIB.so.0...done.
Loaded symbols for /home/raged/MyLIB/memtest/../lib/libMyLIB.so.0
Reading symbols from /usr/lib/libstdc++.so.6...(no debugging symbols found)...done.
...some more libs...
Notice how my library does not give a (no debugging symbols found) error - anyone have any ideas why? As I said before, I am unable to debug this through running the program gdb ./memtest or through debugging the core file.
Thanks for your help.
EDIT It may also be important to note, that (if you didn't realize by path) this library is a local shared library (i.e. I'm using -Wl,-rpath to link/load it)
EDIT2 It seems my version of GDB was out-of-date. Now, I have updated to the latest version from the CVS server (I have also tried latest release version 7.2) and it can "load" symbols. My info sharedlibrary now reads this:
0x00e418b0 0x00e4be74 Yes /home/raged/MyLIB/memtest/../lib/libMyLIB.so.0
However, I am still unable to step through any functions (in the shared library) - anyone have any ideas?
EDIT3 I have also tried to step through linking against a static library (libMyLIB.a) but it still isn't working. My OS is CentOS 5.6; does anyone know of any issues with this system? Also, just another confirmation that my symbols are being loaded (it just can't step through any shared lib function for some reason)
(gdb) sharedlibrary MyLIB
Symbols already loaded for /home/raged/MyLIB/memtest/../lib/libMyLIB.so.0
Answer
I found the reason this wasn't working: I was calling an old function call to initialize a pointer in my test executable. Since the object was never being created, I could never step into the library. Once I updated the function call, all worked well.
That said, if anyone experiences similar issues while all symbols appear to be loaded, be sure to check that all pointers are initialized properly even if they have the correct type.