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    SubjectRe: [tip:perf/core] perf ui annotate browser: Allow toggling addr offset view
    Em Sat, Apr 14, 2012 at 10:55:19AM +0200, Ingo Molnar escreveu:
    >
    > * Arnaldo Carvalho de Melo <acme@redhat.com> wrote:
    >
    > > Em Fri, Apr 13, 2012 at 11:30:52AM -0700, Linus Torvalds escreveu:
    > > > On Fri, Apr 13, 2012 at 11:25 AM, Linus Torvalds
    > > > <torvalds@linux-foundation.org> wrote:
    > > > >
    > > > > <kmem_cache_free>:
    > > > >    1.91 :          push   %rbp
    > > >
    > > > Oh, btw, talking about kmem_cache_free: that one uses altinstructions,
    > > > and so perf report shows the hottest instruction wrong (and I'm not
    > > > talking about "ugly"):
    > >
    > > Well, if we use Masami's disassembler we would use the actual
    > > code as it is being used and not the original DSO that was
    > > later patched by altinstructions.
    >
    > Key would be to use the kernel's live RAM image of instructions.

    Yeah, that is what I meant by "if we use Masami's disassembler" :-)

    > I.e. we should provide a live /proc/vmlinux image in essence: a
    > 'virtual' ELF binary image constructed out of the live kernel
    > RAM image - with no extra RAM overhead. (Maybe with modules
    > included in an intelligent way - although personally I don't use
    > modules when I instrument the kernel)
    >
    > That plus the always-available /proc/kallsyms would offer rather
    > powerful annotation already: without *any* debug info - out of
    > box, on any Linux installation. (This was always the main
    > advantage of /proc/profile and readprofile btw: it worked
    > everywhere while most other profiling solutions needed a
    > debuginfo, etc.)
    >
    > Doing /proc/vmlinux would be different from /dev/mem as it only
    > shows the kernel RAM image, and only in a read-only fashion.
    >
    > Default permissions of /proc/vmlinux should probably track
    > console permissions: it should be possible to allow people
    > sitting in front of the computer to read /proc/vmlinux, while
    > people logged in over the network wouldn't.
    >
    > Doing such a live kernel vmlinux would have other debugging and
    > instrumentation advantages as well: various code patching
    > effects could be checked and observed directly.

    I would say that even for userspace we would love to have such virtual
    ELF files, as code patching is become more common...

    - Arnaldo
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