linux-kernel - Re: [PATCH 1/3] perf script brstackinsn: Fix recovery from LBR/binary mismatch

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Message-ID: <20190930105023.GD9622@kernel.org>
Date:   Mon, 30 Sep 2019 07:50:23 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Andi Kleen <andi@...stfloor.org>
Cc:     jolsa@...nel.org, linux-kernel@...r.kernel.org,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 1/3] perf script brstackinsn: Fix recovery from
 LBR/binary mismatch

Em Fri, Sep 27, 2019 at 04:35:44PM -0700, Andi Kleen escreveu:
> From: Andi Kleen <ak@...ux.intel.com>
> 
> When the LBR data and the instructions in a binary do not match the
> loop printing instructions could get confused and print a long
> stream of bogus <bad> instructions.
> 
> The problem was that if the instruction decoder cannot decode an
> instruction it ilen wasn't initialized, so the loop going through
> the basic block would continue with the previous value.
> 
> Harden the code to avoid such problems:
> - Make sure ilen is always freshly initialized and is 0 for bad
> instructions.
> - Do not overrun the code buffer while printing instructions
> - Print a warning message if the final jump is not on an
> instruction boundary.

Thanks, applied.

- Arnaldo
 
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> ---
>  tools/perf/builtin-script.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
> index e079b34201f2..32b17d51c982 100644
> --- a/tools/perf/builtin-script.c
> +++ b/tools/perf/builtin-script.c
> @@ -1061,7 +1061,7 @@ static int perf_sample__fprintf_brstackinsn(struct perf_sample *sample,
>  			continue;
>  
>  		insn = 0;
> -		for (off = 0;; off += ilen) {
> +		for (off = 0; off < (unsigned)len; off += ilen) {
>  			uint64_t ip = start + off;
>  
>  			printed += ip__fprintf_sym(ip, thread, x.cpumode, x.cpu, &lastsym, attr, fp);
> @@ -1072,6 +1072,7 @@ static int perf_sample__fprintf_brstackinsn(struct perf_sample *sample,
>  					printed += print_srccode(thread, x.cpumode, ip);
>  				break;
>  			} else {
> +				ilen = 0;
>  				printed += fprintf(fp, "\t%016" PRIx64 "\t%s\n", ip,
>  						   dump_insn(&x, ip, buffer + off, len - off, &ilen));
>  				if (ilen == 0)
> @@ -1081,6 +1082,8 @@ static int perf_sample__fprintf_brstackinsn(struct perf_sample *sample,
>  				insn++;
>  			}
>  		}
> +		if (off != (unsigned)len)
> +			printed += fprintf(fp, "\tmismatch of LBR data and executable\n");
>  	}
>  
>  	/*
> @@ -1121,6 +1124,7 @@ static int perf_sample__fprintf_brstackinsn(struct perf_sample *sample,
>  		goto out;
>  	}
>  	for (off = 0; off <= end - start; off += ilen) {
> +		ilen = 0;
>  		printed += fprintf(fp, "\t%016" PRIx64 "\t%s\n", start + off,
>  				   dump_insn(&x, start + off, buffer + off, len - off, &ilen));
>  		if (ilen == 0)
> -- 
> 2.21.0

-- 

- Arnaldo