[Bug 1322784] Re: Firefox crashes in flag_qsort during spellchecker initialization on x86 due to gcc bug

[L. David Baron]

All comment 42 says is that comment 41 is a separate issue from this
bug.  That doesn't make this bug invalid.

** Changed in: gcc-4.8 (Ubuntu)
       Status: Invalid => Confirmed

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https://bugs.launchpad.net/bugs/1322784

Title:
  Firefox crashes in flag_qsort during spellchecker initialization on
  x86 due to gcc bug

Status in The Mozilla Firefox Browser:
  Confirmed
Status in “firefox” package in Ubuntu:
  Confirmed
Status in “gcc-4.8” package in Ubuntu:
  Confirmed

Bug description:
  The most common Firefox crash on Linux in Mozilla's crash-stats system
  is crashes in the function flag_qsort.

  These crashes occur:
   * only on x86 architecture
   * only on Ubuntu packages (and not on Mozilla's builds)
   * on precise and saucy and trusty (based on kernel versions reported with the crashes)
  and appear to be due to a compiler bug in the compiler used to generate Ubuntu's builds.  (It could be a common compiler bug triggered by different compiler options or a compiler bug specific to Ubuntu's gcc.)

  The analysis that leads to the conclusion that this is a compiler bug
  is in https://bugzilla.mozilla.org/show_bug.cgi?id=983817 .  In
  particular, the compiler is miscompiling an access to an element of an
  array of unsigned short as a 32-bit read, and when the unsigned short
  in question is the last one in the allocation and that allocation is
  aligned so that the byte following has a different 0x100000 bit, this
  can lead to crashes.

  The most recent (whenever you follow the link) 7 days of crash reports
  are available at: https://crash-
  stats.mozilla.com/report/list?signature=flag_qsort&product=Firefox&query_type=contains&range_unit=weeks

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