lkml.org 
[lkml]   [2012]   [Apr]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [tip:perf/core] perf ui annotate browser: Allow toggling addr offset view

* 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.

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.

Thanks,

Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2012-04-14 10:57    [W:0.083 / U:0.764 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site