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The current version of perf detects whether or not the perf.data file is written in a different endianness using the attr_size field in the header of the file. This field represents sizeof(struct perf_event_attr) as known to perf record. If the sizes do not match, then perf tries the byte-swapped version. If they match, then the tool assumes a different endianness. The issue with the approach is that it assumes the size of perf_event_attr always has to match between perf record and perf report. However, the kernel perf_event ABI is extensible. New fields can be added to struct perf_event_attr. Consequently, it is not possible to use attr_size to detect endianness. This patch takes another approach by using the magic number written at the beginning of the perf.data file to detect endianness. The magic number is an eight-byte signature. It's primary purpose is to identify (signature) a perf.data file. But it could also be used to encode the endianness. The patch introduces a new value for this signature. The key difference is that the signature is written differently in the file depending on the endianness. Thus, by comparing the signature from the file with the tool's own signature it is possible to detect endianness. The new signature is "PERFILE2". Backward compatiblity with existing perf.data file is ensured. Tested-by: David Ahern <dsahern@gmail.com> Acked-by: David Ahern <dsahern@gmail.com> Cc: Andi Kleen <andi@firstfloor.org> Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com> Cc: Arun Sharma <asharma@fb.com> Cc: David Ahern <dsahern@gmail.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Lin Ming <ming.m.lin@intel.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Roberto Agostino Vitillo <ravitillo@lbl.gov> Cc: Robert Richter <robert.richter@amd.com> Cc: Vince Weaver <vweaver1@eecs.utk.edu> Link: http://lkml.kernel.org/r/1328187288-24395-15-git-send-email-eranian@google.com Signed-off-by: Stephane Eranian <eranian@google.com> Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com> |
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