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    SubjectQuestion about Kernel Reporting Sigfaults in <arch>/mm/fault.c

    [All lines are from 2.6.16's latest git repository from]

    We recently started noticing error messages showing up in the messages file
    every time a user process segfaulted. Doing some investigation, it turns
    out it's only on x86_64 boxen (the other boxes are i386). We traced this
    down to arch/x86_64/mm/fault.c:do_page_fault() (under bad_area_nosemaphore):

    478 if (exception_trace && unhandled_signal(tsk, SIGSEGV)) {
    479 printk(
    480 "%s%s[%d]: segfault at %016lx rip %016lx rsp %016lx error %lx\n",
    481 tsk->pid > 1 ? KERN_INFO : KERN_EMERG,
    482 tsk->comm, tsk->pid, address, regs->rip,
    483 regs->rsp, error_code);
    484 }

    exception_trace is set to 1 (line 296) and not used anywhere else in the file.

    arch/i386/mm/fault.c does not have this.
    arch/sparc64/mm/fault.c does not have this.

    Oddly, sparc/mm/fault.c *does* have (a version of) this, only ifdef'ed out:

    319 #if 0
    320 printk("Fault whee %s [%d]: segfaults at %08lx pc=%08lx\n",
    321 tsk->comm, tsk->pid, address, regs->pc);
    322 #endif

    This leads me to suspect that the segfault reporting in in x86_64 is
    vestigial from a time when it was helpful.

    The question(s): Is this intentional (to have segfaults reported on x86_64,
    and (possibly) nothing else)? Or was "exception_trace" supposed to be a
    flag but never fleshed out?

    I admit, it would be nice to be able to toggle on and off segfault
    reporting in the kernel (from a system administration point of view, this
    is helpful to be able to go back to developers and say 'your program is
    crashing a lot' -- something necessary if you are protecting end-users from
    a lot of core files . . .) on all platforms.

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