Re: [PATCH v4 2/4] perf tools arm64: Add support for get_cpuid_str function.

[Ganapatrao Kulkarni]

On Thu, Aug 10, 2017 at 11:39 PM, Arnaldo Carvalho de Melo
<acme@xxxxxxxxxx> wrote:
> Em Thu, Aug 10, 2017 at 06:15:50PM +0100, Will Deacon escreveu:
>> On Thu, Jul 20, 2017 at 11:26:06AM +0530, Ganapatrao Kulkarni wrote:
>> > function get_cpuid_str returns MIDR string of the first online
>> > cpu from the range of cpus associated with the pmu core device.
>> >
>> > Signed-off-by: Ganapatrao Kulkarni <ganapatrao.kulkarni@xxxxxxxxxx>
>> > ---
>> >  tools/perf/arch/arm64/util/Build    |  1 +
>> >  tools/perf/arch/arm64/util/header.c | 59 +++++++++++++++++++++++++++++++++++++
>> >  2 files changed, 60 insertions(+)
>> >  create mode 100644 tools/perf/arch/arm64/util/header.c
>> >
>> > diff --git a/tools/perf/arch/arm64/util/Build b/tools/perf/arch/arm64/util/Build
>> > index cef6fb3..b1ab72d 100644
>> > --- a/tools/perf/arch/arm64/util/Build
>> > +++ b/tools/perf/arch/arm64/util/Build
>> > @@ -1,3 +1,4 @@
>> > +libperf-y += header.o
>> >  libperf-$(CONFIG_DWARF)     += dwarf-regs.o
>> >  libperf-$(CONFIG_LOCAL_LIBUNWIND) += unwind-libunwind.o
>> >
>> > diff --git a/tools/perf/arch/arm64/util/header.c b/tools/perf/arch/arm64/util/header.c
>> > new file mode 100644
>> > index 0000000..4e25498
>> > --- /dev/null
>> > +++ b/tools/perf/arch/arm64/util/header.c
>> > @@ -0,0 +1,59 @@
>> > +#include <stdio.h>
>> > +#include <stdlib.h>
>> > +#include <api/fs/fs.h>
>> > +#include "header.h"
>> > +
>> > +#define MIDR "/regs/identification/midr_el1"
>> > +#define MIDR_SIZE 128
>> > +
>> > +char *get_cpuid_str(struct perf_pmu *pmu)
>> > +{
>> > +   char *buf = malloc(MIDR_SIZE);
>> > +   char *temp = NULL;
>> > +   char path[PATH_MAX];
>> > +   const char *sysfs = sysfs__mountpoint();
>> > +   int cpu, ret;
>> > +   unsigned long long midr;
>> > +   struct cpu_map *cpus;
>> > +   FILE *file;
>> > +
>> > +   if (!pmu->cpus)
>> > +           return NULL;
>> > +
>> > +   if (!sysfs)
>> > +           return NULL;
>> > +
>> > +   /* read midr from list of cpus mapped to this pmu */
>> > +   cpus = cpu_map__get(pmu->cpus);
>> > +   for (cpu = 0; cpu < cpus->nr; cpu++) {
>> > +           ret = snprintf(path, PATH_MAX,
>> > +                           "%s/devices/system/cpu/cpu%d"MIDR,
>> > +                           sysfs, cpus->map[cpu]);
>> > +           if (ret == PATH_MAX) {
>> > +                   pr_err("sysfs path crossed PATH_MAX(%d) size\n", PATH_MAX);
>> > +                   goto err;
>> > +           }
>> > +
>> > +           file = fopen(path, "r");
>> > +           if (!file)
>> > +                   continue;
>> > +
>> > +           temp = fgets(buf, MIDR_SIZE, file);
>> > +           fclose(file);
>> > +           if (!temp)
>> > +                   continue;
>> > +
>> > +           /* Ignore/clear Variant[23:20] and
>> > +            * Revision[3:0] of MIDR
>> > +            */
>> > +           midr = strtoll(buf, NULL, 16);
>> > +           midr &= (~(0xf << 20 | 0xf));
>> > +           snprintf(buf, MIDR_SIZE, "0x%016llx", midr);
>> > +           cpu_map__put(cpus);
>> > +           return buf;
>> > +   }
>> > +
>> > +err:       cpu_map__put(cpus);
>> > +   free(buf);
>> > +   return NULL;
>> > +}
>>
>> Might just be me, but I found this really difficult to read. I think it
>> works, but having the return at the end of loop is really counter-intuitive.
>>
>> I'll leave it up to Arnaldo, since I can't find any functional problems
>> with this series from the arm64 side.
>
> And it uses malloc(128) and doesn't check its return as well, can you
> please rewrite this having just one return, one refcount drop, etc,
> outside of the loop?
>
> And that fgets() return may be an error, don't you have to check it more
> carefully?
>
> Also please read the snprintf() man page, it doesn't return the number
> of chars it actually wrote, but the number of chars it _would_ write, I
> suggest you use scnprintf() instead.
>
> Also it doesn't count the terminating null byte on what it returns, so
> the check is flawed in that regard as well.

Thanks Arnaldo and Will for the comments.
I will rework this function as suggested in next version.

>
> - Arnaldo
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

thanks
Ganapat