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    SubjectRe: [perf] perf top segfaulting
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    On Fri, Feb 3, 2012 at 8:24 PM, David Daney <david.daney@cavium.com> wrote:
    > On 02/03/2012 04:45 PM, Dan McGee wrote:
    >>
    >> On i686, version 3.2-2, but looks like annotate.c hasn't changed much
    >> since. It sometimes happens within 5 seconds of starting perf,
    >> sometimes much later, but almost always if I leave it running I well
    >> come back to it having segfaulted. When ran with gdb here it took
    >> about 3 minutes; I had a 5 second segfault and a 5 minute segfault
    >> before and after this run as well. I'm not sure what triggers it other
    >> than it isn't user input, as I can start `perf top`, not touch it, and
    >> it will eventually segfault.
    >>
    >
    >
    > I have seen the same thing (basically the same stack trace), so I think what
    > I see is probably closely related.  My failures however are on mips64 based
    > systems.
    >
    > My debugging suggests that this happens when the ABIs used by the running
    > processes are heterogeneous (A mixture of 32-bit and 64-bit processes).
    >  What I see is that all processes use a library with a common name, but
    > differing in paths (/lib32/libc-2.11.3.so and /lib64/libc-2.11.3.so for
    > example).  It looks like perf is confusing the offsets it caches from one
    > library to look up information in the other and since the symbols are in
    > different locations, the resulting erroneous address calculations result in
    > accesses to unmapped portions of perf's address space and you get SIGSEGV.
    >
    > I haven't dug into the code enough to suggest a fix, but I think that at a
    > high hand-waving level, this is what is happening.  I have never observed
    > the failure when using only a single ABI on the system

    Note that in this case, it is a pure 32-bit x86 system, and no library
    changes were going on in the background. So I wouldn't be surprised if
    the causes are similar (or the same), but I don't think I can chalk it
    up to being a single ABI vs multiple ABI problem; i686 only has one
    ABI.

    -Dan
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