linux-kernel - [PATCH] perf record: Fixing record option data type in parse_branch

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Message-ID: <4FBF3CD1.7030603@linux.vnet.ibm.com>
Date:	Fri, 25 May 2012 13:33:29 +0530
From:	Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:	eranian@...gle.com,
	Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
CC:	linux-kernel@...r.kernel.org
Subject: [PATCH] perf record: Fixing record option data type in parse_branch_stack

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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