Re: GCC stack backtraces

[David Daney <ddaney.cavm@gmail.com>]

On 08/29/2012 12:43 AM, Janne Blomqvist wrote:
> On Wed, Aug 29, 2012 at 10:22 AM, Ian Lance Taylor <iant@google.com> wrote:
>> I've spent the last couple of days working on a stack backtrace library.
>>
>> It uses the GCC unwind interface to collect a stack trace, and parses
>> DWARF debug info to get file/line/function information.
> [snip]
>> I expect to use this code not just for GCC proper, but also for libgo
>> (currently libgo uses Go code to parse DWARF, but that is not very
>> satisfactory as that code is only available if it has been imported into
>> the program).  So I put it under a BSD license, although that is open
>> for discussion.  Also in case it finds more uses elsewhere I wrote it in
>> reasonably portable C rather than C++.
>>
>>
>> Does this seem like something we could usefully add to GCC?  Does
>> anybody see any big problems with it?
>
> I haven't looked at the code, but if it is async-signal-safe it could
> be interesting for gfortran. Currently in libgfortran we have a
> backtracing routine, originally written by FX Coudert IIRC, since
> rewritten by yours truly a few times, that uses _Unwind_Backtrace()
> from libgcc and then pipes the output via addr2line, if found. Since
> it's invoked from a signal handler when the program (user program, not
> the compiler!) crashes, it needs to be async-signal-safe. AFAIK the
> current implementation *should* fulfill that requirement. But
> something that would be async-signal-safe and won't need addr2line to
> get symbolic info would be a nice improvement,

libgcj also uses this technique.  If this were merged, it would be 
really nice to retrofit libgcj to use it as well.

Having this capability available from C and C++ code would also be 
really nice.  Several times in the past I have hacked together an 
unwinder by calling _Unwind_Backtrace(), and then decoded the traces 
off-line using addr2line.  An easy, low-overhead way to add 
function/line number information to a trace would be quite welcome.

I would almost say to put it in libgcc along side of 
_Unwind_Backtrace(), but that doesn't seem the proper place for it.  It 
would be very convenient though.


Thanks,
David Daney