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Subject: Re: [PATCH 2/2] perf tools: Improve EOPNOTSUPP error reporting
From:   He Zhe <zhe.he@windriver.com>
To:     catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com,
        alexander.shishkin@linux.intel.com, jolsa@redhat.com,
        namhyung@kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>, mingo@redhat.com,
        acme@kernel.org
References: <20210223082535.48730-1-zhe.he@windriver.com>
 <20210223082535.48730-2-zhe.he@windriver.com>
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Oops, add some supporters from get_maintainer.pl

Zhe

On 2/23/21 4:25 PM, He Zhe wrote:
> There may be multiple reasons for EOPNOTSUPP. Sometimes we cannot determine
> which one it is.
>
> For example, when we set up uprobe with 32-bit perf and arm64 kernel on
> some hardware that does not support sampling/overflow-interrupts,
> $ perf probe -x /lib/libc.so.6 malloc
> $ perf record -e probe_libc:malloc -a ls
>
> Before this patch:
> probe_libc:malloc: PMU Hardware doesn't support sampling/overflow-interrupts. Try 'perf stat'
>
> After this patch:
> probe_libc:malloc: PMU Hardware may not support sampling/overflow-interrupts. Try 'perf stat'.
> Some 64-bit architectures may not support 32-bit instruction probing.
>
> Signed-off-by: He Zhe <zhe.he@windriver.com>
> ---
>  tools/perf/util/evsel.c | 18 ++++++++++--------
>  1 file changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index 1bf76864c4f2..aa56511ddf60 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -2697,22 +2697,24 @@ int evsel__open_strerror(struct evsel *evsel, struct target *target,
>  		break;
>  	case EOPNOTSUPP:
>  		if (evsel->core.attr.aux_output)
> -			return scnprintf(msg, size,
> -	"%s: PMU Hardware doesn't support 'aux_output' feature",
> +			printed += scnprintf(msg + printed, size,
> +	"%s: PMU Hardware may not support 'aux_output' feature.\n",
>  					 evsel__name(evsel));
>  		if (evsel->core.attr.sample_period != 0)
> -			return scnprintf(msg, size,
> -	"%s: PMU Hardware doesn't support sampling/overflow-interrupts. Try 'perf stat'",
> +			printed += scnprintf(msg + printed, size,
> +	"%s: PMU Hardware doesn't support sampling/overflow-interrupts. Try 'perf stat'.\n",
>  					 evsel__name(evsel));
>  		if (evsel->core.attr.precise_ip)
> -			return scnprintf(msg, size, "%s",
> -	"\'precise\' request may not be supported. Try removing 'p' modifier.");
> +			printed += scnprintf(msg + printed, size, "%s",
> +	"\'precise\' request may not be supported. Try removing 'p' modifier.\n");
>  #if defined(__i386__) || defined(__x86_64__)
>  		if (evsel->core.attr.type == PERF_TYPE_HARDWARE)
> -			return scnprintf(msg, size, "%s",
> +			printed += scnprintf(msg + printed, size, "%s",
>  	"No hardware sampling interrupt available.\n");
>  #endif
> -		break;
> +		scnprintf(msg + printed, size, "%s",
> +	"Some 64-bit architectures may not support 32-bit instruction uprobe.\n");
> +		return;
>  	case EBUSY:
>  		if (find_process("oprofiled"))
>  			return scnprintf(msg, size,