Em Sat, Apr 14, 2012 at 10:55:19AM +0200, Ingo Molnar escreveu: > > * 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. 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 -- 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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