Re: [PATCH] perf record: Fixing record option data type in parse_branch_stack

[Stephane Eranian]

Hi,

It should be something like that instead:

diff --git a/tools/perf/perf.h b/tools/perf/perf.h
index 8a9687e..c9ca7c4 100644
--- a/tools/perf/perf.h
+++ b/tools/perf/perf.h
@@ -228,7 +228,7 @@ struct perf_record_opts {
        unsigned int freq;
        unsigned int mmap_pages;
        unsigned int user_freq;
-       int          branch_stack;
+       u64          branch_stack;
        u64          default_interval;
        u64          user_interval;
 };


On Fri, May 25, 2012 at 10:03 AM, Anshuman Khandual
<khandual@xxxxxxxxxxxxxxxxxx> wrote:
> perf record: Fixing record option data type in parse_branch_stack
>
> Â Â Â ÂCurrently parse_branch_stack does not update record.opts.branch_stack
> Â Â Â Âvalue in powerpc architecture. opt->value is declared as int in struct
> Â Â Â Âperf_record_opts. But is worked on as uint64_t isnide the function.
> Â Â Â ÂThis breaks functionality in poweprc due to bit representation
> Â Â Â Âof uint64_t which is inaccessible as int.
>
> Signed-off-by: Anshuman Khandual <khandual@xxxxxxxxxxxxxxxxxx>
> ---
> Âtools/perf/builtin-record.c | Â Â2 +-
> Â1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index e5cb084..161c0f1 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -677,7 +677,7 @@ parse_branch_stack(const struct option *opt, const char *str, int unset)
> Â Â Â Â PERF_SAMPLE_BRANCH_KERNEL Â Â Â|\
> Â Â Â Â PERF_SAMPLE_BRANCH_HV)
>
> - Â Â Â uint64_t *mode = (uint64_t *)opt->value;
> + Â Â Â int *mode = (int *)opt->value;
> Â Â Â Âconst struct branch_mode *br;
> Â Â Â Âchar *s, *os = NULL, *p;
> Â Â Â Âint ret = -1;
> --
> 1.7.9.5
>
>
>
> On Friday 25 May 2012 10:57 AM, Anshuman Khandual wrote:
>
>> This code is breaking in powerpc systems.
>>
>> (1) 'opt->value' gets updated inside the function parse_branch_stack via
>> Â Â dereferencing a (uint64_t *) type casted pointer.
>>
>> (2) But the value is not accessible when we again use opt->value via
>> Â Â dereferencing a (int *) type casted pointer.
>>
>> (3) As a result record.opts.branch_stack remains 0 and unchanged by parse_branch_stack
>>
>> This is caused by bit representation of 'uint64_t' and 'int' in powerpc systems. Bytes update
>> for the data (when accessed trough (uint64_t *) casting) is no longer available to the
>> data when accessed through (int *) type casting. Verified this from bit representation of
>> the data (accessed through both type casting methods).
>>
>> However this problem does not seem to be present on an Intel box. Integer dereferencing of
>> the opt->value still gives the value which was updated as (uint64_t).
>>
>> All this problem would not have been there if we had used (int *) instead of (uint64_t *) in
>> the first place inside parse_branch_stack function.
>>
>> On Thursday 24 May 2012 02:51 PM, Anshuman Khandual wrote:
>>
>>> Hey Stephane,
>>>
>>> Just wondering why we used the type casting of (uint64_t *) on a data
>>> which is defined as "int" in the structure of "perf_record_opts".
>>>
>>> struct perf_record_opts {
>>> Â Â Â Â struct perf_target target;
>>>     bool     call_graph;
>>>     bool     group;
>>>     bool     inherit_stat;
>>>     bool     no_delay;
>>>     bool     no_inherit;
>>>     bool     no_samples;
>>>     bool     pipe_output;
>>>     bool     raw_samples;
>>>     bool     sample_address;
>>>     bool     sample_time;
>>>     bool     sample_id_all_missing;
>>>     bool     exclude_guest_missing;
>>>     bool     period;
>>> Â Â Â Â unsigned int freq;
>>> Â Â Â Â unsigned int mmap_pages;
>>> Â Â Â Â unsigned int user_freq;
>>>     int     Âbranch_stack;
>>> Â Â Â Â u64 Â Â Â Â Âdefault_interval;
>>> Â Â Â Â u64 Â Â Â Â Âuser_interval;
>>> };
>>>
>>> static int
>>> parse_branch_stack(const struct option *opt, const char *str, int unset)
>>> {
>>> #define ONLY_PLM \
>>> Â Â Â Â (PERF_SAMPLE_BRANCH_USER Â Â Â Â|\
>>> Â Â Â Â ÂPERF_SAMPLE_BRANCH_KERNEL Â Â Â|\
>>> Â Â Â Â ÂPERF_SAMPLE_BRANCH_HV)
>>>
>>> Â Â Â Â uint64_t *mode = (uint64_t *)opt->value;
>>> --
>>> Regards
>>> Anshuman Khandual
>>>
>>> --
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>>
>>
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>
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