[Webkit-unassigned] [Bug 93763] New: WTF::monotonicallyIncreasingTime() compiled wrong by GCC 4.2

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=93763

           Summary: WTF::monotonicallyIncreasingTime() compiled wrong by
                    GCC 4.2
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Macintosh
        OS/Version: Unspecified
            Status: UNCONFIRMED
          Severity: Critical
          Priority: P2
         Component: Web Template Framework
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: tobias.netzel at googlemail.com


Created an attachment (id=157863)
 --> (https://bugs.webkit.org/attachment.cgi?id=157863&action=review)
better(?) implementation of WTF::monotonicallyIncreasingTime()

The current implementation of monotonicallyIncreasingTime() doesn't return the desired results, at least when compiled with GCC 4.2 on Mac OS X 10.5 PowerPC. While the result is indeed a monotonically increasing value of seconds, it overflows at a value of approx. 1001.xxxxxx, continuing with 0. This is probably caused by the double conversions done (or rather NOT done) in the right places. Maybe clang compiles this different than GCC or the current implementation works correctly on 64 bit (integer) platforms only or it's because of the 32 bit PowerPC having a 64 bit FPU; I didn't examine the assembly output.

The implementation in the attached patch is borrowed from libauto (http://www.opensource.apple.com/source/libauto/libauto-141.2/auto_zone.cpp) and returns the iMO correct value.

I stumbled over this problem with the current implementation because occasionally WebCore::ThreadTimers::sharedTimerFiredInternal() got stuck in an infinite loop when fireTime and timeToQuit had both values close to 1001.xxxxxx . While with the implementation from the patch this problems seems to be gone, it is probably still there but much much less probable to occur. What I want to say is that WebCore::ThreadTimers::sharedTimerFiredInternal() MUST be made overflow safe.

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