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Date: Wed, 23 Jul 2014 14:48:49 +0200
From: Jiri Olsa <jolsa@redhat.com>
To: Adrian Hunter <adrian.hunter@intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>, linux-kernel@vger.kernel.org,
        David Ahern <dsahern@gmail.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Namhyung Kim <namhyung@gmail.com>, Paul Mackerras <paulus@samba.org>,
        Stephane Eranian <eranian@google.com>
Subject: Re: [PATCH 49/52] perf tools: Build programs to copy 32-bit
 compatibility VDSOs
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On Tue, Jul 22, 2014 at 04:17:58PM +0300, Adrian Hunter wrote:

SNIP

> index 1f67aa0..45ab040 100644
> --- a/tools/perf/config/Makefile
> +++ b/tools/perf/config/Makefile
> @@ -604,6 +604,27 @@ ifdef HAVE_KVM_STAT_SUPPORT
>      CFLAGS += -DHAVE_KVM_STAT_SUPPORT
>  endif
>  
> +ifeq (${IS_64_BIT}, 1)
> +  ifndef NO_PERF_READ_VDSO32
> +    CAN_DO := $(shell echo "main() {}" | ${CC} -m32 -x c - >/dev/null 2>/dev/null && echo 1 || echo 0)
> +    ifneq (${CAN_DO}, 1)
> +      NO_PERF_READ_VDSO32 := 1
> +    endif
> +  endif
> +  ifneq (${IS_X86_64}, 1)
> +    NO_PERF_READ_VDSOX32 := 1
> +  endif
> +  ifndef NO_PERF_READ_VDSOX32
> +    CAN_DO := $(shell echo 'main() {}' | ${CC} -mx32 -x c - >/dev/null 2>/dev/null && echo 1 || echo 0)
> +    ifneq (${CAN_DO}, 1)
> +      NO_PERF_READ_VDSOX32 := 1
> +    endif
> +  endif

please move those check into feature config code under config/features/..

SNIP

> +++ b/tools/perf/perf-read-vdso.c
> @@ -0,0 +1,59 @@
> +#include <stdio.h>
> +#include <string.h>
> +
> +#define VDSO__MAP_NAME "[vdso]"
> +
> +static int find_vdso_map(void **start, void **end)
> +{
> +	FILE *maps;
> +	char line[128];
> +	int found = 0;
> +
> +	maps = fopen("/proc/self/maps", "r");
> +	if (!maps) {
> +		fprintf(stderr, "vdso: cannot open maps\n");
> +		return -1;
> +	}
> +
> +	while (!found && fgets(line, sizeof(line), maps)) {
> +		int m = -1;
> +
> +		/* We care only about private r-x mappings. */
> +		if (2 != sscanf(line, "%p-%p r-xp %*x %*x:%*x %*u %n",
> +				start, end, &m))
> +			continue;
> +		if (m < 0)
> +			continue;
> +
> +		if (!strncmp(&line[m], VDSO__MAP_NAME,
> +			     sizeof(VDSO__MAP_NAME) - 1))
> +			found = 1;
> +	}
> +
> +	fclose(maps);
> +	return !found;
> +}

hum, any easy way to use/share find_vdso_map from vdso.c?
I guess this way is more straighforward and clear.. it's
probably not worthy for function this simple

jirka