* Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxx> 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-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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