linux-kernel - Re: [PATCH] perf: fix bug mismatch with -c option definition

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Message-ID: <20100517141910.GA14367@ghostprotocols.net>
Date:	Mon, 17 May 2010 11:19:10 -0300
From:	Arnaldo Carvalho de Melo <acme@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	linux-kernel@...r.kernel.org, peterz@...radead.org, mingo@...e.hu,
	paulus@...ba.org, davem@...emloft.net, fweisbec@...il.com,
	perfmon2-devel@...ts.sf.net, eranian@...il.com
Subject: Re: [PATCH] perf: fix bug mismatch with -c option definition

Em Mon, May 17, 2010 at 12:04:01PM +0200, Stephane Eranian escreveu:
>   The -c option defines the user requested sampling period. It was implemented
>   using an unsigned int variable but the type of the option was OPT_LONG. Thus,
>   the option parser was overwriting memory belonging to other variables, namely
>   the mmap_pages leading to a zero page sampling buffer. The bug was exposed
>   only when compiling at -O0, probably because the compiler was padding
>   variables at higher optimization levels.

Well spotted!
 
>   This patch fixes this problem by declaring user_interval as u64. This also
>   avoids wrap-around issues for large period on 32-bit systems.
>  
>   Signed-off-by: Stephane Eranian <eranian@...gle.com>
> --
>  tools/perf/builtin-record.c |    8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index 0f467cf..78f64cc 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -33,8 +33,8 @@ enum write_mode_t {
>  
>  static int			*fd[MAX_NR_CPUS][MAX_COUNTERS];
>  
> -static unsigned int		user_interval 			= UINT_MAX;
> -static long			default_interval		=      0;
> +static u64			user_interval			= ULLONG_MAX;
> +static u64			default_interval		=      0;

The parsing code uses this for OPT_LONG:

        case OPTION_LONG:
                if (unset) {
                        *(long *)opt->value = 0;
                        return 0;
                }
                if (opt->flags & PARSE_OPT_OPTARG && !p->opt) {
                        *(long *)opt->value = opt->defval;
                        return 0;
                }
                if (get_arg(p, opt, flags, &arg))
                        return -1;
                *(long *)opt->value = strtol(arg, (char **)&s, 10);

So I think we should augment the parsing code to have OPTION_ULONG, and,
for handling u64, OPTION_ULLONG.

I'll add that and then modify your patch to use it.

- Arnaldo
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