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

[Mark Lam]

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