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Message-ID: <CABPqkBS6cdUkKgC1Jp_pzMWxDKZYJtomoZUx6g2z739y=TkPAw@mail.gmail.com>
Date: Fri, 25 May 2012 10:44:27 +0200
From: Stephane Eranian <eranian@...gle.com>
To: Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Cc: Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf record: Fixing record option data type in parse_branch_stack
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@...ux.vnet.ibm.com> wrote:
> perf record: Fixing record option data type in parse_branch_stack
>
> Currently parse_branch_stack does not update record.opts.branch_stack
> value in powerpc architecture. opt->value is declared as int in struct
> perf_record_opts. But is worked on as uint64_t isnide the function.
> This breaks functionality in poweprc due to bit representation
> of uint64_t which is inaccessible as int.
>
> Signed-off-by: Anshuman Khandual <khandual@...ux.vnet.ibm.com>
> ---
> tools/perf/builtin-record.c | 2 +-
> 1 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)
> PERF_SAMPLE_BRANCH_KERNEL |\
> PERF_SAMPLE_BRANCH_HV)
>
> - uint64_t *mode = (uint64_t *)opt->value;
> + int *mode = (int *)opt->value;
> const struct branch_mode *br;
> char *s, *os = NULL, *p;
> int 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
>> dereferencing a (uint64_t *) type casted pointer.
>>
>> (2) But the value is not accessible when we again use opt->value via
>> 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 {
>>> 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;
>>> unsigned int freq;
>>> unsigned int mmap_pages;
>>> unsigned int user_freq;
>>> int branch_stack;
>>> u64 default_interval;
>>> u64 user_interval;
>>> };
>>>
>>> static int
>>> parse_branch_stack(const struct option *opt, const char *str, int unset)
>>> {
>>> #define ONLY_PLM \
>>> (PERF_SAMPLE_BRANCH_USER |\
>>> PERF_SAMPLE_BRANCH_KERNEL |\
>>> PERF_SAMPLE_BRANCH_HV)
>>>
>>> uint64_t *mode = (uint64_t *)opt->value;
>>> --
>>> Regards
>>> Anshuman Khandual
>>>
>>> --
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>>
>>
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>
>
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