linux-kernel - Re: [bug] wrong result of android callchain

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Date:	Tue, 5 Jan 2016 11:20:55 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	He Kuang <hekuang@...wei.com>
Cc:	"mingo@...hat.com" <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>, rabin.vincent@...s.com,
	namhyung@...nel.org, Wang Nan <wangnan0@...wei.com>,
	linux-kernel@...r.kernel.org, mark.rutland@....com,
	will.deacon@....com
Subject: Re: [bug] wrong result of android callchain

On Tue, Jan 05, 2016 at 05:14:37PM +0800, He Kuang wrote:
> I found a wrong result of aarch64 callchain when using perf script on
> a android phone.

Might help to include the AARGH64 people then.. seeing I have no clue
about all that. Cc's added, email preserved etc..

> 
> Here's the callchain record fragment from the output of perf script:
> 
>   init   369 [002]   339.970607: raw_syscalls:sys_enter: NR 22 (b, 7fd9e360a0, 10, ffffffff, 0, 8)
>                      ...
>                    230ac [unknown] (/system/lib64/libsurfaceflinger.so)
>                     11a0 main (/system/bin/surfaceflinger)
>                    1c3fc __libc_init (/system/lib64/libc.so)
>                      fd0 _start (/system/bin/surfaceflinger)
>                     29ec __dl__start (/system/bin/linker64)
> 
> The fault occured in the '[unknown]' line, from objdump result of
> /system/bin/surfaceflinger, we can see the branch instruction before
> 0x11a0:
> 
>  # objdump /system/bin/surfaceflinger
>     1198:       f9400fe0        ldr     x0, [sp,#24]
>     119c:       97ffff05        bl      db0 <_ZN7android14SurfaceFlinger3runEv@plt>
>     11a0:       f9400be8        ldr     x8, [sp,#16]
>     11a4:       b40000c8        cbz     x8, 11bc <main+0x150>
> 
> The function '_ZN7android14SurfaceFlinger3runEv' is located at 0x3a094
> ~ 0x3a0ac in libsurfaceflinger.so, but perf misparsed that value to
> 0x230ac:
> 
>  # objdump libsurfaceflinger.so
>   000000000003a094 <_ZN7android14SurfaceFlinger3runEv>:
>     3a094:       a9be4ff4        stp     x20, x19, [sp,#-32]!
>     3a098:       a9017bfd        stp     x29, x30, [sp,#16]
>     3a09c:       910043fd        add     x29, sp, #0x10
>     3a0a0:       910c0013        add     x19, x0, #0x300
>     3a0a4:       aa1303e0        mov     x0, x19
>     3a0a8:       97fff12f        bl      36564 <_ZN7android12MessageQueue11waitMessageEv>
>     3a0ac:       17fffffe        b       3a0a4 <_ZN7android14SurfaceFlinger3runEv+0x10>
> 
> There's a difference of 0x17000 between those two offsets, it seems
> that this value is the VirtAddr of this dynamic library.
> 
>  # readelf -a libsurfaceflinger.so
>   Program Headers:
>     Type           Offset             VirtAddr           PhysAddr
>                    FileSiz            MemSiz              Flags  Align
>     LOAD           0x0000000000000000 0x0000000000017000 0x0000000000017000
>                    0x0000000000057258 0x0000000000057258  R E    1000
> 
> 
> 
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