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SubjectRe: [PATCH v2 07/15] x86/lib/copy_user_64.S: Convert to ALTERNATIVE_2

* Ingo Molnar <mingo@kernel.org> wrote:

> Ha! There's a neat alternatives debugging trick with perf that you
> might not know about: if you run 'perf top' as root then perf will
> use /proc/kcore to disassemble the live kernel image and if you look
> at the assembly output of hot functions then you'll see the real,
> patched instructions on the live kernel, not the vmlinux
> instructions.
>
> I have two enhancement suggestions to the perf tooling developers for
> this usecase:

and I've got a bugreport as well, when I use the kcore annotations on
'fput' symbol (i.e. running 'perf top' as root), go into the
disassembly window and then try to exit that window, then I get this
segfault:

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7ffff3c41700 (LWP 29134)]
lock__delete (ops=0x7fffec001818) at util/annotate.c:219
219 ins__delete(ops->locked.ops);
(gdb) bt
#0 lock__delete (ops=0x7fffec001818) at util/annotate.c:219
#1 0x000000000046e568 in disasm_line__free (dl=0x7fffec0017e0) at util/annotate.c:619
#2 0x00000000004f0743 in symbol__tui_annotate (sym=<optimized out>, map=<optimized out>, evsel=evsel@entry=0x83d770, hbt=hbt@entry=0x7ffff3c40e60)
at ui/browsers/annotate.c:976
#3 0x00000000004f0973 in hist_entry__tui_annotate (he=he@entry=0x151ba40, evsel=evsel@entry=0x83d770, hbt=hbt@entry=0x7ffff3c40e60) at ui/browsers/annotate.c:835
#4 0x00000000004f5685 in perf_evsel__hists_browse (evsel=0x83d770, nr_events=nr_events@entry=1,
helpline=helpline@entry=0x51d350 "For a higher level overview, try: perf top --sort comm,dso", left_exits=left_exits@entry=false, hbt=hbt@entry=0x7ffff3c40e60,
min_pcnt=<optimized out>, env=0x83de40) at ui/browsers/hists.c:1716
#5 0x00000000004f7ae4 in perf_evlist__tui_browse_hists (evlist=0x7cbb90, help=help@entry=0x51d350 "For a higher level overview, try: perf top --sort comm,dso",
hbt=hbt@entry=0x7ffff3c40e60, min_pcnt=<optimized out>, env=<optimized out>) at ui/browsers/hists.c:2006
#6 0x0000000000435850 in display_thread_tui (arg=0x7fffffffa580) at builtin-top.c:582
#7 0x00007ffff7bc40a5 in start_thread (arg=0x7ffff3c41700) at pthread_create.c:309
#8 0x00007ffff5fe4cfd in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111

using latestest tools/perf.

Thanks,

Ingo


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