linux-kernel - Re: [PATCH v2 2/5] perf: util: use capstone disasm engine to show assembly instructions

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Date: Wed, 17 Jan 2024 09:54:59 +0100
From: Thomas Richter <tmricht@...ux.ibm.com>
To: Changbin Du <changbin.du@...wei.com>,
        Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
        changbin.du@...il.com
Subject: Re: [PATCH v2 2/5] perf: util: use capstone disasm engine to show
 assembly instructions

On 1/17/24 06:11, Changbin Du wrote:
> Currently, the instructions of samples are shown as raw hex strings
> which are hard to read. x86 has a special option '--xed' to disassemble
> the hex string via intel XED tool.
> 
> Here we use capstone as our disassembler engine to give more friendly
> instructions. We select libcapstone because capstone can provide more
> insn details. Perf will fallback to raw instructions if libcapstone is
> not available.
> 
> The advantages compared to XED tool:
>  * Support arm, arm64, x86-32, x86_64 (more could be supported),
>    xed only for x86_64.
>  * Immediate address operands are shown as symbol+offs.
> 
> Signed-off-by: Changbin Du <changbin.du@...wei.com>
> ---
>  tools/perf/builtin-script.c  |   8 +--
>  tools/perf/util/Build        |   1 +
>  tools/perf/util/print_insn.c | 123 +++++++++++++++++++++++++++++++++++
>  tools/perf/util/print_insn.h |  14 ++++
>  4 files changed, 141 insertions(+), 5 deletions(-)
>  create mode 100644 tools/perf/util/print_insn.c
>  create mode 100644 tools/perf/util/print_insn.h> 
..

> diff --git a/tools/perf/util/print_insn.c b/tools/perf/util/print_insn.c
> new file mode 100644
> index 000000000000..fe035efe8cf6
> --- /dev/null
> +++ b/tools/perf/util/print_insn.c
> @@ -0,0 +1,123 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Instruction binary disassembler based on capstone.
> + *
> + * Author(s): Changbin Du <changbin.du@...wei.com>
> + */
> +#include "print_insn.h"
> +#include <stdlib.h>
> +#include <string.h>
> +#include <stdbool.h>
> +#include "util/debug.h"
> +#include "util/symbol.h"
> +#include "machine.h"
> +
> +size_t sample__fprintf_insn_raw(struct perf_sample *sample, FILE *fp)
> +{
> +	int printed = 0;
> +
> +	for (int i = 0; i < sample->insn_len; i++)
> +		printed += fprintf(fp, "%02x ", (unsigned char)sample->insn[i]);
> +	return printed;
> +}
> +
> +#ifdef HAVE_LIBCAPSTONE_SUPPORT
> +#include <capstone/capstone.h>
> +
> +static int capstone_init(struct machine *machine, csh *cs_handle)
> +{
> +	cs_arch arch;
> +	cs_mode mode;
> +
> +	if (machine__is(machine, "x86_64")) {
> +		arch = CS_ARCH_X86;
> +		mode = CS_MODE_64;
> +	} else if (machine__normalized_is(machine, "x86")) {
> +		arch = CS_ARCH_X86;
> +		mode = CS_MODE_32;
> +	} else if (machine__normalized_is(machine, "arm64")) {
> +		arch = CS_ARCH_ARM64;
> +		mode = CS_MODE_ARM;
> +	} else if (machine__normalized_is(machine, "arm")) {
> +		arch = CS_ARCH_ARM;
> +		mode = CS_MODE_ARM + CS_MODE_V8;
> +	} else if (machine__normalized_is(machine, "s390x")) {

        } else if (machine__normalized_is(machine, "s390")) {                 

> +		arch = CS_ARCH_SYSZ;
> +		mode = CS_MODE_BIG_ENDIAN;
> +	} else {
> +		return -1;
> +	}

I have debugged your reworked patch this morning and discovered that
it was not working. The issue turned out to be function machine__normalized_is().
The first parameter is passed to several functions before the comparison.
The calls executed are

   machine__normhalized_is()
   +--> perf_env__arch() --> called for first parameter.
        +--> normalize_arch() --> always returns "s390"

We need to change the second parameter to "s390" without the trailing x
as indicated above. Sorry for the confusion.

Thanks a lot.
Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany
--
IBM Deutschland Research & Development GmbH

Vorsitzender des Aufsichtsrats: Wolfgang Wendt

Geschäftsführung: David Faller

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