Reading symbols from dynamic symbol table

Jaimon Jose jjaimon@Yahoo.com
Wed Dec 8 06:51:00 GMT 2004


Yes.  This is ELF

Here is an example.  I create a shared library with the following 
functions.
int func3(void)
{
    char *nullptr = 0;
    printf("func3\n");
    *nullptr = '\0';
}
int func2(void)
{
    printf("func2\n");
    func3();
}
extern "C" int func_entry(void)
{
     printf("func_entry\n");
     func2();
}

I create the sharedlibrary and link to another program that calls 
func_entry.
$>g++ -shared -o libprgshared.so  prgshared.cpp
$>nm --defined-only libprgshared.so
00001aa0 A __bss_start
00000740 t call_gmon_start
00001aa0 b completed.1
00001a70 d __CTOR_END__
00001a6c d __CTOR_LIST__
00000890 t __do_global_ctors_aux
00000770 t __do_global_dtors_aux
00001900 d __dso_handle
00001a78 d __DTOR_END__
00001a74 d __DTOR_LIST__
00001984 A _DYNAMIC
00001aa0 A _edata
00001aa4 A _end
000008c4 T _fini
000007e0 t frame_dummy
00001980 r __FRAME_END__
0000086c T func_entry
00001a80 A _GLOBAL_OFFSET_TABLE_
000006f8 T _init
00001a7c d __JCR_END__
00001a7c d __JCR_LIST__
00001904 d p.0
0000084e T _Z5func2v
00000828 T _Z5func3v
$>g++ -O2 -o prgmain prgmain.cpp libprgshared.so
$>./prgmain
$>gdb ./prgmain core
(gdb) where
#0  0x40018848 in func3 () from libprgshared.so
#1  0x40018869 in func2 () from libprgshared.so
#2  0x40018887 in func_entry () from ibprgshared.so
#3  0x080485ca in main ()

Now I create the shared object with --retain-symbols-file by just 
exporting only func_entry
$>g++ -shared -o libprgshared.so -Wl,--retain-symbols-file 
-Wl,prgshared.sym  prgshared.cpp
$>nm --defined-only libprgshared.so
0000086c T func_entry
$>nm -D --defined-only libprgshared.so
00001aa0 A __bss_start
00001984 A _DYNAMIC
00001aa0 A _edata
00001aa4 A _end
000008c4 T _fini
0000086c T func_entry
00001a80 A _GLOBAL_OFFSET_TABLE_
000006f8 T _init
0000084e T _Z5func2v
00000828 T _Z5func3v

I link this against my main program and look at the new core file.
(gdb) where
#0  0x40018848 in ?? () from libprgshared.so
#1  0x40018869 in ?? () from libprgshared.so
#2  0x40018887 in func_entry () from libprgshared.so
#3  0x080485ca in main ()

Frame #0 and #1 no longer shows the function name though it is available 
in the dynamic section of shared library.  How do I force gdb to read 
symbols from this section?

I'm using the following versions of programs
$>ld -V
GNU ld version 2.15.90.0.1.1 20040303 (SuSE Linux)
   Supported emulations:
    elf_i386
    i386linux
    elf_x86_64
$>gdb --version
GNU gdb 6.1
Copyright 2004 Free Software Foundation, Inc
$>>gcc --version
gcc (GCC) 3.3.3 (SuSE Linux)
Copyright (C) 2003 Free Software Foundation, Inc.
thanks,
--jaimon

Daniel Jacobowitz wrote the following on 12/08/2004 10:15 AM:
> On Wed, Dec 08, 2004 at 10:03:39AM +0530, Jaimon Jose wrote:
> 
>>I have few libraries built with --retain-symbols-file ld option.  I 
>>can't see the correct symbols when I open the core file due to this. It 
>>always shows the stack trace with few exported symbols+offset.  However, 
>>'nm' is able to read all the symbols from dynamic symbol table.  Is 
>>there a way to instruct gdb to read symbols from dynamic symbol table?
> 
> 
> It normally does - is this ELF?  You'll have to investigate why it
> isn't working.
> 



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