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Re: i386-linux signal backtraces broken
- From: Mark Kettenis <kettenis at chello dot nl>
- To: Daniel Jacobowitz <drow at mvista dot com>
- Cc: gdb at sources dot redhat dot com
- Date: 12 Oct 2002 19:50:38 +0200
- Subject: Re: i386-linux signal backtraces broken
- References: <20021010184739.GA15971@nevyn.them.org>
Daniel Jacobowitz <drow@mvista.com> writes:
> There's only one problem here. On my desktop (Debian GNU/Linux, glibc
> 2.2.5), there are two copies of sigaction in a dynamically linked
> executable. One of them's in libc.so.6 and the other is in ld-linux.so.2.
> The only __restore symbol we find is in ld-linux.so.2; this seems to be
> because we leave a symbol table in ld-linux.so.2 (probably for the
> debugger's benefit, so that it can find _dl_debug_state) - but we strip
> libc.so.6.
How unfortunate. I'd recommend using an unstripped libc.so.6 when
doing any serious debugging, but I guess that won't trick the Debian
folks into distributing an unstripped libc.
> Unfortunately, the application gets the copy of __restore that is in
> libc.so.6. Which is right after a function whose name appears in the
> dynamic symbol table (sigaction). So it's considered to be part of
> sigaction, and NAME is "sigaction".
>
> We have two choices, that I see:
> - Call the code inspection functions always
> - Call the code inspection functions if the name is sigaction, taking
> advantage of the glibc implementation detail that sigaction is the
> only exported name for this function that I can see, and they are
> implemented right after it in the same file.
We could also modify glibc such that __restore and __restore_rt get
included in libc.so's dynamic symbol table. Or perhaps we could
modify GDB such that it scans libc.so.6 for signal trampolines when it
is loaded.
> Option (A) is a performance hit. Option (B) is, well, a little fragile.
I don't think implementing (B) makes the code more fragile than it
already is.
Mark