Re: [PATCH RFT 00/16] perf tools: Use generic syscall scripts for all archs

[Charlie Jenkins <charlie@rivosinc.com>]

On Mon, Nov 04, 2024 at 03:35:33PM -0800, Charlie Jenkins wrote:
> On Mon, Nov 04, 2024 at 02:03:28PM -0800, Ian Rogers wrote:
> > On Mon, Nov 4, 2024 at 1:32 PM Charlie Jenkins <charlie@rivosinc.com> wrote:
> > >
> > > On Mon, Nov 04, 2024 at 10:13:18PM +0100, Arnd Bergmann wrote:
> > > > On Mon, Nov 4, 2024, at 22:06, Charlie Jenkins wrote:
> > > > > Standardize the generation of syscall headers around syscall tables.
> > > > > Previously each architecture independently selected how syscall headers
> > > > > would be generated, or would not define a way and fallback onto
> > > > > libaudit. Convert all architectures to use a standard syscall header
> > > > > generation script and allow each architecture to override the syscall
> > > > > table to use if they do not use the generic table.
> > > > >
> > > > > As a result of these changes, no architecture will require libaudit, and
> > > > > so the fallback case of using libaudit is removed by this series.
> > > > >
> > > > > Testing:
> > > > >
> > > > > I have tested that the syscall mappings of id to name generation works
> > > > > as expected for every architecture, but I have only validated that perf
> > > > > trace compiles and runs as expected on riscv, arm64, and x86_64.
> > > > >
> > > > > Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
> > > >
> > > > Thanks for doing this, I had plans to do this myself, but hadn't
> > > > completed that bit so far. I'm travelling at the moment, so I'm
> > > > not sure I have time to look at it in enough detail this week.
> > > >
> > > > One problem I ran into doing this previously was the incompatible
> > > > format of the tables for x86 and s390, which have conflicting
> > > > interpretations of what the '-' character means. It's possible
> > > > that this is only really relevant for the in-kernel table,
> > > > not the version in tools.
> > > >
> > >
> > > I don't think that is an issue for this usecase because the only
> > > information that is taken from the syscall table is the number and the
> > > name of the syscall. '-' doesn't appear in either of these columns!
> > 
> > This is cool stuff. An area that may not be immediately apparent for
> > improvement is that the x86-64 build only has access to the 64-bit
> > syscall table. Perhaps all the syscall tables should always be built
> > and then at runtime the architecture of the perf.data file, etc. used
> > to choose the appropriate one. The cleanup to add an ELF host #define
> > could help with this:
> > https://lore.kernel.org/linux-perf-users/20241017002520.59124-1-irogers@google.com/
> 
> Oh that's a great idea! I think these changes will make it more seamless
> to make that a reality.
> 
> > 
> > Ultimately I'd like to see less arch code as it inherently makes cross
> > platform worker harder. That doesn't impact this work which I'm happy
> > to review.
> 
> Yeah I agree. Reducing arch code was the motivation for this change.
> There was the issue a couple weeks ago that caused all architectures
> that used libaudit to break from commit 7a2fb5619cc1fb53 ("perf trace:
> Fix iteration of syscall ids in syscalltbl->entries"), so this change
> will eliminate that source of difference between architectures.
> 
> - Charlie
> 
> > 
> > Thanks,
> > Ian

Let me know if you have any feedback on this series!

- Charlie