[webkit-dev] Change WTFCrash to not trash the crash site register state.

[Filip Pizlo]

I like this idea.  I’ve wanted this for a while.

Can you explain why your approach doesn’t inline a store to 0xbbadbeef, so that this aspect of the current behavior is preserved?

-Filip


> On Feb 8, 2016, at 11:55 AM, Mark Lam <mark.lam at apple.com> wrote:
> 
> Hi WebKit folks,
> 
> For non-debug OS(DARWIN) builds, I would like to change WTFCrash()’s implementation into an inlined function that has a single inlined asm statement that issues a breakpoint trap.  The intent is to crash directly in the caller’s frame and preserve the register values at the time of the crash.  As a result, for non-debug OS(DARWIN) builds, crashes due to failed RELEASE_ASSERTs will now show up in crash reports as crashing due to EXC_BREAKPOINT (SIGTRAP) instead of a EXC_BAD_ACCESS (SIGSEGV) on address 0xbbadbeef.
> 
> This is in contrast to the current implementation where WTFCrash() is a function that calls a lot of handler / callback functions before actually crashing.  As a result, by the time it crashes, the caller’s register values has most likely been trashed by all the work that the WTFCrash and the handlers / callbacks do.  The register values in the captured crash report will, therefore, no longer be useful for crash site analysis. 
> 
> You can find the patch for this change at https://bugs.webkit.org/show_bug.cgi?id=153996.  This change will only be applied for non-debug OS(DARWIN) builds for now.  I’m leaving all other build build configurations with the existing WTFCrash() implementation and behavior.
> 
> Does anyone have any opinion / feedback on this change?
> 
> Thanks.
> 
> Regards,
> Mark
> 
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