linux-kernel - Re: [PATCH 49/52] perf tools: Build programs to copy 32-bit compatibility VDSOs

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Date:	Wed, 23 Jul 2014 16:55:03 +0300
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	Jiri Olsa <jolsa@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>
CC:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Namhyung Kim <namhyung@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 49/52] perf tools: Build programs to copy 32-bit compatibility
 VDSOs

On 07/23/2014 03:48 PM, Jiri Olsa wrote:
> 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/..

I will look at doing that.

> 
> 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

Would have to create another source file and include it.
I am not sure it is worth it.  Maybe Arnaldo can decide?

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