Re: [PATCH v3] perf symbols: Consolidate symbol fixup issue

[Jiri Olsa]

On Fri, Mar 06, 2020 at 09:57:58AM +0800, Leo Yan wrote:
> After copying Arm64's perf archive with object files and perf.data file
> to x86 laptop, the x86's perf kernel symbol resolution fails.  It
> outputs 'unknown' for all symbols parsing.
> 
> This issue is root caused by the function elf__needs_adjust_symbols(),
> x86 perf tool uses one weak version, Arm64 (and powerpc) has rewritten
> their own version.  elf__needs_adjust_symbols() decides if need to parse
> symbols with the relative offset address; but x86 building uses the weak
> function which misses to check for the elf type 'ET_DYN', so that it
> cannot parse symbols in Arm DSOs due to the wrong result from
> elf__needs_adjust_symbols().
> 
> The DSO parsing should not depend on any specific architecture perf
> building; e.g. x86 perf tool can parse Arm and Arm64 DSOs, vice versa.
> And confirmed by Naveen N. Rao that powerpc64 kernels are not being
> built as ET_DYN anymore and change to ET_EXEC.
> 
> This patch removes the arch specific functions for Arm64 and powerpc and
> changes elf__needs_adjust_symbols() as a common function.
> 
> In the common elf__needs_adjust_symbols(), it checks an extra condition
> 'ET_DYN' for elf header type.  With this fixing, the Arm64 DSO can be
> parsed properly with x86's perf tool.
> 
> Before:
> 
>   # perf script
>   main  3258          1          branches:                 0 [unknown] ([unknown]) => ffff800010c4665c [unknown] ([kernel.kallsyms])
>   main  3258          1          branches:  ffff800010c46670 [unknown] ([kernel.kallsyms]) => ffff800010c4eaec [unknown] ([kernel.kallsyms])
>   main  3258          1          branches:  ffff800010c4eaec [unknown] ([kernel.kallsyms]) => ffff800010c4eb00 [unknown] ([kernel.kallsyms])
>   main  3258          1          branches:  ffff800010c4eb08 [unknown] ([kernel.kallsyms]) => ffff800010c4e780 [unknown] ([kernel.kallsyms])
>   main  3258          1          branches:  ffff800010c4e7a0 [unknown] ([kernel.kallsyms]) => ffff800010c4eeac [unknown] ([kernel.kallsyms])
>   main  3258          1          branches:  ffff800010c4eebc [unknown] ([kernel.kallsyms]) => ffff800010c4ed80 [unknown] ([kernel.kallsyms])
> 
> After:
> 
>   # perf script
>   main  3258          1          branches:                 0 [unknown] ([unknown]) => ffff800010c4665c coresight_timeout+0x54 ([kernel.kallsyms])
>   main  3258          1          branches:  ffff800010c46670 coresight_timeout+0x68 ([kernel.kallsyms]) => ffff800010c4eaec etm4_enable_hw+0x3cc ([kernel.kallsyms])
>   main  3258          1          branches:  ffff800010c4eaec etm4_enable_hw+0x3cc ([kernel.kallsyms]) => ffff800010c4eb00 etm4_enable_hw+0x3e0 ([kernel.kallsyms])
>   main  3258          1          branches:  ffff800010c4eb08 etm4_enable_hw+0x3e8 ([kernel.kallsyms]) => ffff800010c4e780 etm4_enable_hw+0x60 ([kernel.kallsyms])
>   main  3258          1          branches:  ffff800010c4e7a0 etm4_enable_hw+0x80 ([kernel.kallsyms]) => ffff800010c4eeac etm4_enable+0x2d4 ([kernel.kallsyms])
>   main  3258          1          branches:  ffff800010c4eebc etm4_enable+0x2e4 ([kernel.kallsyms]) => ffff800010c4ed80 etm4_enable+0x1a8 ([kernel.kallsyms])
> 
> v3: Changed to check for ET_DYN across all architectures.
> 
> v2: Fixed Arm64 and powerpc native building.
> 
> Reported-by: Mike Leach <mike.leach@xxxxxxxxxx>
> Signed-off-by: Leo Yan <leo.yan@xxxxxxxxxx>
> Reviewed-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>

Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>

thanks,
jirka