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 17:44:12 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Adrian Hunter <adrian.hunter@...el.com>
Cc:	Jiri Olsa <jolsa@...hat.com>,
	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

Em Wed, Jul 23, 2014 at 04:55:03PM +0300, Adrian Hunter escreveu:
> 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.

Ok, probably this can be done in a follow up patch, Jiri?
 
> > 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?

I think it is, either do direct sourcing with #include or add it to a
linking list for the binaries that use it.

- Arnaldo
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