Re: [PATCH v2] tools: perf: tests: Fix code reading for riscv

[Ian Rogers]

On Wed, Dec 18, 2024 at 10:41 AM Arnaldo Carvalho de Melo
<acme@xxxxxxxxxx> wrote:
>
> On Tue, Dec 17, 2024 at 04:30:15PM -0800, Charlie Jenkins wrote:
> > On Tue, Dec 17, 2024 at 04:18:32PM -0800, Ian Rogers wrote:
> > > On Tue, Dec 17, 2024 at 3:52 PM Charlie Jenkins <charlie@xxxxxxxxxxxx> wrote:
> > > > After binutils commit e43d876 which was first included in binutils 2.41,
> > > > riscv no longer supports dumping in the middle of instructions. Increase
> > > > the objdump window by 2-bytes to ensure that any instruction that sits
> > > > on the boundary of the specified stop-address is not cut in half.
>
> > > > Signed-off-by: Charlie Jenkins <charlie@xxxxxxxxxxxx>
>
> > > Reviewed-by: Ian Rogers <irogers@xxxxxxxxxx>
>
> > > > A binutils patch has been sent as well to fix this in objdump [1].
>
> > > > Link: https://sourceware.org/pipermail/binutils/2024-December/138139.html [1]
>
> > > > Changes in v2:
> > > > - Do objdump version detection at runtime (Ian)
> > > > - Link to v1: https://lore.kernel.org/r/20241216-perf_fix_riscv_obj_reading-v1-0-b75962660a9b@xxxxxxxxxxxx
>
> > > > --- a/tools/perf/tests/code-reading.c
> > > > @@ -183,9 +244,30 @@ static int read_via_objdump(const char *filename, u64 addr, void *buf,
> > > >         const char *fmt;
> > > >         FILE *f;
> > > >         int ret;
> > > > +       u64 stop_address = addr + len;
> > > > +
> > > > +       if (IS_ENABLED(__riscv)) {
>
> > > Not sure if there is a consistency issue here. Elsewhere we're just
> > > using ifdef, such as:
> > > https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/include/dwarf-regs.h?h=perf-tools-next#n69
>
> > I don't have any strong feelings about that. I can change it to be an
> > ifdef. On other lists I have been told to use IS_ENABLED whenever
> > possible, but it's only a small difference.
>
> Can't we just use uname here?
>
> So that we don't use kconfig.h since its not used in tools/perf/ and
> makes it looks like perf is in lockstep with the kernel source tree
> version it was compiled from?
>
> $ git grep kconfig.h tools/perf/
> $
>
> BTW, what would happen if I collected a perf.data file on x86_64 and
> would read it in a RiscV machine with such a objdump version? The same
> problem?

This code is in tests hence thinking that a separate fix is needed for
that problem. Hopefully the use of elf machine/flags tackles it:
https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/include/dwarf-regs.h?h=perf-tools-next#n25
We are getting somewhat disassembler heavy. We have llvm as a library,
capstone as a library, binutils objdump and llvm objdump. Given the
pain with parsing text, could we lose the objdumps? Similarly for
addr2line?

Thanks,
Ian