Messages in this thread | | | Date | Thu, 5 Nov 2009 10:01:18 -0200 | From | Arnaldo Carvalho de Melo <> | Subject | Re: [PATCH 1/1] perf symbols: Use the buildids if present |
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Em Thu, Nov 05, 2009 at 09:27:33AM +0100, Ingo Molnar escreveu: > > * Masami Hiramatsu <mhiramat@redhat.com> wrote: > > > Arnaldo Carvalho de Melo wrote: > >> From: Arnaldo Carvalho de Melo<acme@redhat.com> > >> > >> Now 'perf record' will intercept PERF_RECORD_MMAP calls, creating a > >> linked list of DSOs, then when the session finishes, it will traverse > >> this list and read the buildids, stashing them at the end of the file > >> and will set up a new feature bit in the header bitmask. > >> > >> 'perf report' will then notice this feature and populate the 'dsos' list > >> and set the build ids. > >> > >> When reading the symtabs it will refuse to load from a file that doesn't > >> have the same build id. > >> > >> Example: > >> > >> [root@doppio ~]# perf report | head > >> /home/acme/bin/perf with build id b1ea544ac3746e7538972548a09aadecc5753868 not found, continuing without symbols > >> # Samples: 2621434559 > >> # > >> # Overhead Command Shared Object Symbol > >> # ........ ............... ............................. ...... > >> # > >> 7.91% init [kernel] [k] read_hpet > >> 7.64% init [kernel] [k] mwait_idle_with_hints > >> 7.60% swapper [kernel] [k] read_hpet > >> 7.60% swapper [kernel] [k] mwait_idle_with_hints > >> 3.65% init [kernel] [k] 0xffffffffa02339d9 > >> [root@doppio ~]# > >> > >> In this case the 'perf' binary was an older one, vanished, so it the symbols > >> probably wouldn't match. > >> > >> Next patches will support the kernel as well, reading the build id notes for it > >> and the modules from /sys. > > > > Great! then I can use it on 'perf probe' to check the dwarf binary is > > same as running kernel.
Yes, at perf record I'll always get the build id from /sys/kernel/notes and insert it in the buildid table, then at 'perf report' it will match it against the file from where it is getting the symbols, be it /proc/kallsyms or the vmlinux file, be it one specified in the command line, found on some standard location (/sys/kernel/`uname -r`/build/vmlinux) or from some new /sys file, as Ingo suggests.
The resulting infrastructure can then be used in perf probe to match running kernel buildid against the vmlinux used.
> >> Another patch should also introduce a new plumbing command: > >> > >> 'perf list-buildids' > >> > >> that will then be used in porcelain that is distro specific to > >> fetch -debuginfo packages where such buildids are present. This will in turn > >> allow for one to run 'perf record' in one machine and 'perf report' in another. > > > > Hmm, so, will this command list up all debuginfo files with buildids? > > If so, can it also find a kernel binary built locally? > > Arnaldo, how about adding the kernel binary's build path to > /sys/kernel/notes, during the kernel build? (With perhaps a .config > override as well, for package builds.) > > That object might or might not exist, and if it does not exist, or if > there is a buildid mismatch, we can fall back to 'well known' places for > kernel/module binaries.
Yeah, I'll do that. I haven't touched much of the kernel because I'm trying to use what is already there to the fullest extent.
But there are things to do in the kernel (and wiki), yeah:
1. atomically generate mmap events, keeping the synthesize mmap/comm events that traverses /proc/ pidspace just for older kernels
2. insert the buildid in the PERF_RECORD_MMAP events
3. kernel binary build path
4. write such entries in the perf wiki TODO page
:-)
- Arnaldo
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