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Date: Fri, 1 Jul 2016 10:05:41 +0800
From: Hekuang <hekuang@...wei.com>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
CC: Wang Nan <wangnan0@...wei.com>, Jiri Olsa <jolsa@...nel.org>,
"Peter Zijlstra" <peterz@...radead.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: perf unwind: Odd message about x86 unwind
hi
在 2016/6/30 20:06, Arnaldo Carvalho de Melo 写道:
> Hi He,
>
> While testing a patch by Peter Zijlstra to the --stdio
> annotation code I came accross these messages:
>
> [acme@...et linux]$ perf annotate __vdso_gettimeofday 2>&1 | head -20
> unwind: target platform=x86 is not supported
> unwind: target platform=x86 is not supported
> unwind: target platform=x86 is not supported
> unwind: target platform=x86 is not supported
> Percent | Source code & Disassembly of perf-vdso.so-E5tFUx for cycles:u
> -----------------------------------------------------------------------------
> :
> :
> :
> : Disassembly of section .text:
> :
> : 0000000000000cd0 <__vdso_gettimeofday@@LINUX_2.6>:
> 0.00 : cd0: push %rbp
> 0.00 : cd1: mov %rsp,%rbp
> 0.00 : cd4: push %r15
> 0.00 : cd6: push %r14
> 0.00 : cd8: push %r13
> 0.00 : cda: push %r12
> 0.00 : cdc: push %rbx
> 0.00 : cdd: sub $0x10,%rsp
> [acme@...et linux]$
>
> And bisected it down to:
>
> commit 52ffe0ff02fc053a025c381d5808e9ecd3206dfe
> Author: He Kuang <hekuang@...wei.com>
> Date: Fri Jun 3 03:33:22 2016 +0000
>
> perf callchain: Support x86 target platform
>
> Support x86(32-bit) cross platform callchain unwind.
>
> Signed-off-by: He Kuang <hekuang@...wei.com>
> Acked-by: Jiri Olsa <jolsa@...nel.org>
>
> --------------------------------------------------
>
> The source code where this message is emitted is:
>
> struct unwind_libunwind_ops __weak *local_unwind_libunwind_ops;
> <SNIP>
> unwind__prepare_access()
> {
> struct unwind_libunwind_ops *ops = local_unwind_libunwind_ops;
> <SNIP>
> if (!strcmp(arch, "x86")) {
> if (dso_type != DSO__TYPE_64BIT)
> ops = x86_32_unwind_libunwind_ops;
> }
> <SNIP>
> if (!ops) {
> pr_err("unwind: target platform=%s is not supported\n", arch);
> return -1;
> }
>
> So, this should fallback to local_unwind_libunwind_ops, why is this not being
> set properly?
>
> Feature detection says:
>
> ... libunwind: [ on ]
> ... libdw-dwarf-unwind: [ on ]
>
> This is:
>
> [acme@...et linux]$ uname -a
> Linux jouet 4.5.7-300.fc24.x86_64 #1 SMP Wed Jun 8 18:12:45 UTC 2016 x86_64 x86_64 x86_64 GNU/Linuxo
>
> Can you please check this?
I think it's because of the perf.data contains both 32bit/64bit
threads while perf is only build with local unwind(unwind for
x86_64).
Then I have a simple test for this:
$ file hello_x86_64
hello_x86_64: ELF 64-bit LSB executable, x86-64, version 1 (SYSV),
dynamically linked (uses shared libs), for GNU/Linux 3.0.0,
BuildID[sha1]=adc94932cbcb2be80f3b62df530b8c109f40478a, not strippe
$ file hello_i686
hello_i686: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV),
dynamically linked (uses shared libs), for GNU/Linux 4.5.0, not stripped
$ perf record -o perf.data.x86_64_singlethread hello_x86_64
$ perf record -o perf.data.x86_64_allcpu -a hello_x86_64
$ perf record -o perf.data.i686_singlethread hello_i686
$ perf record -o perf.data.i686_allcpu -a hello_i686
Now I get 4 perf.data files:
ID name 32bit 64bit
1 perf.data.x86_64_singlethread N Y
2 perf.data.x86_64_allcpu N Y
3 perf.data.i686_singlethread Y N
4 perf.data.i686_allcpu Y Y
Because perf only supports local unwind(for x86_64), cases
contain 32bit thread should show the warnings, i.e. case3 and
case4. And perf.data contains only 32bit threads will show nothing
except the warnings while the one contains both 32bit/64bit will
show warnings for 32bit thread and annoate the 64bit thread.
Then check:
$ perf annotate -i perf.data.x86_64_singlethread
Percent | Source code & Disassembly of hello for cycles:pp
----------------------------------------------------------------
:
:
:
: Disassembly of section .text:
:
: 00000000004005c0 <fib>:
: fib():
: #endif
$ perf annotate -i perf.data.x86_64_allcpu
Percent | Source code & Disassembly of hello for cycles:pp
----------------------------------------------------------------
:
:
:
: Disassembly of section .text:
:
: 00000000004005c0 <fib>:
: fib():
: #endif
:
: volatile int z = 0;
:
: int fib(int x)
$ perf annotate -i perf.data.i686_singlethread
unwind: target platform=x86 is not supported
unwind: target platform=x86 is not supported
unwind: target platform=x86 is not supported
$ perf annotate -i perf.data.i686_allcpu
unwind: target platform=x86 is not supported
unwind: target platform=x86 is not supported
unwind: target platform=x86 is not supported
Percent | Source code & Disassembly of perf for cycles:pp
---------------------------------------------------------------
:
:
:
: Disassembly of section .text:
:
: 0000000000442a8f <record__mmap_read>:
: record__mmap_read():
:
: return backward_rb_find_range(data, mask, head, start,
end);
: }
The result is the same as we expected, so if your case matches
the case4, the result is right. But I think we can improve the
warning message for not confusing the users.
Thank you.
> - Arnaldo
>
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