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

From: Arnaldo Carvalho de Melo <acme@kernel.org>
To: Charlie Jenkins <charlie@rivosinc.com>
Cc: Ian Rogers <irogers@google.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Namhyung Kim <namhyung@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Jiri Olsa <jolsa@kernel.org>,
	Adrian Hunter <adrian.hunter@intel.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Bill Wendling <morbo@google.com>,
	Justin Stitt <justinstitt@google.com>,
	linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-riscv@lists.infradead.org
Subject: Re: [PATCH v2] tools: perf: tests: Fix code reading for riscv
Date: Wed, 18 Dec 2024 15:41:32 -0300	[thread overview]
Message-ID: <Z2MXXFhUzoQmW4xV@x1> (raw)
In-Reply-To: <Z2IXl5cuKQJInJb0@ghost>

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@rivosinc.com> 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@rivosinc.com>

> > Reviewed-by: Ian Rogers <irogers@google.com>

> > > 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@rivosinc.com

> > > --- 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?

- Arnaldo