Re: [PATCH v2] perf symbols: Consolidate symbol fixup issue

["Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>]

Leo Yan wrote:
> Hi Naveen,
> 
> On Thu, Mar 05, 2020 at 04:32:30PM +0530, Naveen N. Rao wrote:
>> Leo Yan wrote:
<snip>
>> > In the common elf__needs_adjust_symbols(), it checks elf header and 
>> > if
>> > the machine type is one of Arm64/ppc/ppc64, it checks extra condition
>> > for 'ET_DYN'.  Finally, 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])
>> > 
>> 
>> I am not able to reproduce this since powerpc64 kernels are not being built
>> as ET_EXEC anymore.
> 
> Thanks for reviewing!
> 
> Based on the context, I think you mean powerpc64 kernels are not being
> built as ET_DYN anymore (and now change to ET_EXEC).

D'uh, indeed, sorry!

> 
>> > v2: Fixed Arm64 and powerpc native building.
>> > 
>> > Reported-by: Mike Leach <mike.leach@linaro.org>
>> > Signed-off-by: Leo Yan <leo.yan@linaro.org>
>> > ---
>> >  tools/perf/arch/arm64/util/Build            |  1 -
>> >  tools/perf/arch/arm64/util/sym-handling.c   | 19 -------------------
>> >  tools/perf/arch/powerpc/util/Build          |  1 -
>> >  tools/perf/arch/powerpc/util/sym-handling.c | 10 ----------
>> >  tools/perf/util/symbol-elf.c                |  8 +++++++-
>> >  5 files changed, 7 insertions(+), 32 deletions(-)
>> >  delete mode 100644 tools/perf/arch/arm64/util/sym-handling.c
>> > 
<snip>
>> > diff --git a/tools/perf/util/symbol-elf.c 
>> > b/tools/perf/util/symbol-elf.c
>> > index 1965aefccb02..ee788ac67415 100644
>> > --- a/tools/perf/util/symbol-elf.c
>> > +++ b/tools/perf/util/symbol-elf.c
>> > @@ -704,8 +704,14 @@ void symsrc__destroy(struct symsrc *ss)
>> >  	close(ss->fd);
>> >  }
>> > 
>> > -bool __weak elf__needs_adjust_symbols(GElf_Ehdr ehdr)
>> > +bool elf__needs_adjust_symbols(GElf_Ehdr ehdr)
>> >  {
>> > +	if (ehdr.e_machine == EM_AARCH64 ||
>> > +	    ehdr.e_machine == EM_PPC ||
>> > +	    ehdr.e_machine == EM_PPC64)
>> > +		return ehdr.e_type == ET_EXEC || ehdr.e_type == ET_REL ||
>> > +		       ehdr.e_type == ET_DYN;
>> > +
>> >  	return ehdr.e_type == ET_EXEC || ehdr.e_type == ET_REL;
>> 
>> Patch looks good to me. However:
> 
> Can I add your review tag?

Yes:
Reviewed-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>

> 
>> This is only used for checking kernel, so I wonder if we can simply include
>> check for ET_DYN across all architectures? This would only matter if there
>> are architectures building their kernel as ET_DYN that _don't_ want to
>> adjust symbols.
> 
> Seems only Arm64 enables the link option '-share' for LDFLAGS_vmlinux;
> I confirmed with below command:
> 
> $ find arch -name 'Makefile' -exec grep -n '\-share' {} + | grep vmlinux
> arch/arm64/Makefile:21:LDFLAGS_vmlinux          += -shared -Bsymbolic -z notext -z norelro \
> 
> Also reviewed the output for searching '\-share' for all Makefiles under
> 'arch' folder, many architectures use it for vdso but only Arm64 enables
> '-share' for vmlinux linkage.  If so, your suggestion is valid and we
> can simply include check for ET_DYN for all archs (and it's better to
> add comment for this).
> 
> I'd like to wait a bit for anyone has other ideas, and if no objection
> will send out new patch for this.

Sure, thanks for checking.


- Naveen