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

[Naveen N. Rao]

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@xxxxxxxxxx>
> > > Signed-off-by: Leo Yan <leo.yan@xxxxxxxxxx>
> > > ---
> > >  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@xxxxxxxxxxxxxxxxxx>

> > 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