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From: Pedro Alves <pedro@codesourcery.com>
To: gdb-patches@sourceware.org
Subject: Re: [patch] solib-svr4.c - allow reading linkmap info from core without  executable
Date: Wed, 10 Jun 2009 22:07:00 -0000
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Cc: Aleksandar Ristovski <aristovski@qnx.com>
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On Friday 29 May 2009 21:41:52, Aleksandar Ristovski wrote:
> Hello,
> 
> This small patch allows solib-svr4.c to attempt to read 
> linkmap info from core file when executable binary is not given.
> 
> e.g.:
> $ gdb --core testsuite/gdb.base/bigcore.corefile
> ...
> (gdb) info sharedlibrary
> No shared libraries loaded at this time.
> (gdb)
> 
> after patch:
> 
> $ ./gdb --nx --core  testsuite/gdb.base/bigcore.corefile
> GNU gdb (GDB) 6.8.50.20090529-cvs
> ...
> (gdb) info shared
>  From        To          Syms Read   Shared Object Library
> 0x4cb3e470  0x4cb58844  No          /lib/libm.so.6
> 0x4ca18dd0  0x4cafe490  No          /lib/libc.so.6
> 0x4c9e5880  0x4c9fa8ef  No          /lib/ld-linux.so.2
> (gdb)

Cool.

>    if (info->debug_base == 0 && svr4_have_link_map_offsets ())
>      {
> -      if (exec_bfd != NULL
> +      if ((exec_bfd != NULL
>           && bfd_get_flavour (exec_bfd) == bfd_target_elf_flavour)
> +         || (core_bfd != NULL
> +             && bfd_get_flavour (core_bfd) == bfd_target_elf_flavour))
>         info->debug_base = elf_locate_base ();
>      }

Are there live debugging cases (archs?, PIE?) (e.g., "target remote" 
without specifying an executable) where letting elf_locate_base
try to read the debug base from the target's auxv (scan_dyntag_auxv)
will work?  It would mean that removing the exec_bfd checks instead
of adding core_bfd checks, would still improve your case, while
letting other cases benefit as well.

-- 
Pedro Alves