Re: ia64 failing tst-backtrace4 due to not enough debug info

[Mike Frysinger <vapier at gentoo dot org>]

On Monday 30 December 2013 09:12:22 Joseph S. Myers wrote:
> On Mon, 30 Dec 2013, Mike Frysinger wrote:
> > it looks like a limitation in the libunwind logic (part of gcc) ?  the
> > ia64
> 
> I believe ia64 might use either libgcc unwind code or separate libunwind.

libunwind is packaged w/gcc itself and that's what my system is using.  so 
it's technically a sep lib (i.e. it's a dedicated shared lib), but it's still 
somewhat in the realm of the gcc project considering the code is shipped in 
the gcc tarball.

> > backtrace code uses the x86_64 file and that just calls _Unwind_* funcs
> > that come via gcc.  which means i should bounce this to upstream gcc and
> > not worry about the test failure in glibc right ?  i've never poked into
> > the unwind lib too closely before ...
> 
> I don't think it can usefully be reported to GCC until you've traced the
> backtracing process yourself and identified either (a) a case where you
> can describe exactly what's wrong with the unwind information generated by
> GCC compared to what you say it should generate that would allow
> backtracing here or (b) a case where the unwind information is sufficient
> but one of the _Unwind_* functions, that you've identified as coming from
> libgcc, is handling it in an identified incorrect or suboptimal way.

when i attach with gdb, the backtrace command shows the full stack trace.  but 
calling backtrace() at the same point shows the limited output i mentioned 
earlier.  if this glibc test isn't sufficient (and it's not like it's 
complicated code -- can easily replace the test-skeleton.c usage with a main() 
that calls do_test() and get the same result), then i'll probably bail at this 
point and just mark it as a known failure.  learning the inner details of 
libunwind and the generated info is something i'll put off until next x-mas 
break.
-mike

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