Re: [PATCH] RFC. User space backtrace on segv

[Neil Horman <nhorman@redhat.com>]

Alex Bennee wrote:
> Hi,
> 
> I hacked up this little patch to dump the stack and attempt to generate
> a back-trace for errant user-space tasks.
> 
> What:
> 
> Generates a back-trace of the user application on (in this case) a segv
> caused by an unaligned access. This particular patch is against 2.4.22
> on the SH which is what I'm working with but there no reason it couldn't
> be more generalised.
> 
> How:
> 
> Its not the most intelligent approach as it basically walks up the stack
> reading values and seeing if the address corresponds to one of the
> processes executable VMA's. If it matches it assumes its the return
> address treats that section as a "frame"
> 
> Why:
> 
> I work with embedded systems and for a myriad of reasons doing a full
> core dump of the crashing task is a pain. Often just knowing the
> immediate call stack and local variables is enough to look at what went
> wrong with objdump -S.
> 
> Questions:
> 
> Have I replicated anything that is already hidden in the code base?
> Would this be useful (as a CONFIG_ option) for embedded systems?
> 


IIRC, there is already a backtrace function defined for most arches in 
the c library.  in execinfo.h there is a family of backtrace functions 
that can unwind the stack fairly well for most arches, and store the 
trace in a post SIGSEGV-safe fashion.

Neil

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