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SubjectRe: fix callgraphs of 32-bit processes on 64-bit kernels.
On 03/15/2010 05:34 PM, Török Edwin wrote:
> Hi,
>
> Callgraph profiling 32-bit apps on a 64-bit kernel doesn't work.
> The reason is that perf_callchain_user tries to read a stackframe with 64-bit
> pointers, which is wrong for a 32-bit process.
>
> This patch fixes that, and I am almost able to get nice callgraph profiles
> from 32-bit apps now! (except for some problems with perf itself when tracing
> kernel modules, see [1])
>
> Page-faults can be traced nicely (sid-ia32 is a 32-bit chroot):
>
> $ sudo perf record -e page-faults -f -g /home/edwin/sid-ia32/usr/bin/glxgears
> $ sudo perf report
> ...
> 45.33% libc-2.10.2.so [.] __GI_memcpy
> |
> --- __GI_memcpy
> _mesa_BufferDataARB
> _mesa_meta_Clear
> radeonUserClear
> r700Clear
> _mesa_Clear
> 0x8049367
> 0x804a6ba
> __libc_start_main
> 0x8049111
>
> 16.96% libc-2.10.2.so [.] __GI_memset
> |
> --- __GI_memset
> _tnl_init_vertices
> _swsetup_CreateContext
> r600CreateContext
> driCreateNewContext
> dri2CreateNewContext
> 0xf77ab7dd
> 0xf7783c67
> 0xf778514c
> 0x804974f
> 0x804a33d
> __libc_start_main
> 0x8049111
>
> And CPU cycles can be traced too in userspace:
> $ sudo perf record -f -g /home/edwin/sid-ia32/usr/bin/glxgears
> $ sudo perf report --sort comm,dso
> [...]
> 44.97% glxgears r600_dri.so
> |
> |--5.85%-- r700SendSPIState
> | radeonEmitState
> | r700DrawPrims
> | |
> | |--95.45%-- vbo_save_playback_vertex_list
> | | execute_list
> | | _mesa_CallList
> | | neutral_CallList
> | | |
> | | |--38.10%-- 0x80494a8
> | | | 0x804a6ba
> | | | __libc_start_main
> | | | 0x8049111
> [....]
> 40.00% glxgears [kernel]
> |
> |--3.14%-- copy_user_generic_string
> | |
> | |--71.70%-- 0xffffffffa01b4493
> | | 0xffffffffa01b7c0b
> | | 0xffffffffa018b45b
> | | 0xffffffffa00ca927
> | | 0xffffffffa01c524e
> | | compat_sys_ioctl
> | | sysenter_dispatch
> | | 0xf77ca430
> | | drmCommandWriteRead
> | | 0xf74d7ab5
> | | 0xf74d89a4
> | | rcommonFlushCmdBufLocked
> | | rcommonFlushCmdBuf
> | | radeonFlush
> | | _mesa_flush
> | | _mesa_Flush
> | | 0xf775f270
> | | 0x804a6d5
> | | __libc_start_main
> | | 0x8049111
> | |
> | |--15.09%-- 0xffffffffa01c524e
> | | compat_sys_ioctl
> | | sysenter_dispatch
> | | 0xf77ca430
> | | drmCommandWriteRead
>
> [1] But there is a problem with the perf tool: it can't trace addresses in
> kernel modules. This is a problem regardless if the traced app is 32-bit or
> 64-bit; and regardless if I do callgraph profiling or not.
> See the above trace, where the kernel addresses have all ffffffffa0* without a
> symbol name.
>
> If I look at /proc/kallsyms I can guess the symbols, for example
> 0xffffffffa01b4493 is probably this one:
> ffffffffa01b4411 t r600_cs_packet_parse [radeon]
>
> If I record/report without callgraph its the same problem:
> [...]
> 24.01% glxgears [kernel] [k] 0xffffffffa01b4ee9
> 3.96% glxgears libdrm_radeon.so.1.0.0 [.] cs_gem_write_reloc
> 3.53% glxgears r600_dri.so [.] r700SendSPIState
> 2.77% glxgears r600_dri.so [.] r700DrawPrims
> 1.99% glxgears r600_dri.so [.] r700SendVSConsts
>
> Kernel symbol for 0xffffffffa01b4ee9 is not shown, I can guess it is this one
> (hey it was an exact match!):
> ffffffffa01b4ee9 t r600_packet3_check [radeon]
>
> It would be good if perf knew how to lookup symbols in kernel modules!

BTW perf report -m -k /home/edwin/builds/linux-2.6/vmlinux doesn't show
the symbols either.

>
> Best regards,
> --Edwin

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