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Date: Fri, 25 May 2012 10:57:59 +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: Re: perf record: why we used type casting of (uint64_t *) instead of int 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 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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