[Webkit-unassigned] [Bug 153996] New: Changed WTFCrash to not trash the crash site register state.

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Mon Feb 8 11:31:40 PST 2016


            Bug ID: 153996
           Summary: Changed WTFCrash to not trash the crash site register
    Classification: Unclassified
           Product: WebKit
           Version: WebKit Local Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: mark.lam at apple.com

When doing post-mortem crash site analysis using data from crash reports, it is immensely valuable to be able to infer the crashing program's state from the register values at crash time.  However, for RELEASE_ASSERT failures, we crash using WTFCrash(), and WTFCrash() is currently implemented as a function call that, in turn, calls a lot of other functions to do crash handling before actually crashing.  As a result, the register values captured in the crash reports are not likely to still contain the values used by the caller function that failed the RELEASE_ASSERT.

This patch aims to remedy this issue for non-debug builds on OS(DARWIN) ports.  It does so by changing WTFCrash() into an inlined function that has an inlined asm statement to issues the CPU specific breakpoint trap instruction.  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.

For debug and non-DARWIN builds, WTFCrash() behavior currently remains unchanged.

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