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SubjectRe: [bug] wrong result of android callchain
On Tue, Jan 05, 2016 at 11:20:55AM +0100, Peter Zijlstra wrote:
> 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..

It looks like the issue is in the perf tool, where it fails to resolve
the address to a symbol correctly.

> >
> > 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

This reminds me of:

http://lkml.kernel.org/r/1435162623-20075-1-git-send-email-will.deacon@arm.com

but that was all vdso-specific. Can you look at what gets passed to objdump?

Will


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