lkml.org 
[lkml]   [2011]   [Sep]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH] perf: make perf.data more self-descriptive (v4)


On 09/16/2011 09:19 AM, Peter Zijlstra wrote:
> On Fri, 2011-09-16 at 08:50 -0600, David Ahern wrote:
>>
>> ppc data file: header->magic 454c494646524550
>> x86 data file: header->magic 454c494646524550
>>
> Ok then we need to fix that magic thing..

Right, but it breaks backwards/forwards compatibility. e.g.,

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index 73fa59e..603a8bb9 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -65,9 +65,7 @@ char *perf_header__find_event(u64 id)
return NULL;
}

-static const char *__perf_magic = "PERFFILE";
-
-#define PERF_MAGIC (*(u64 *)__perf_magic)
+#define PERF_MAGIC 0x5045524646494c45ULL // "PERFFILE"

struct perf_file_attr {
struct perf_event_attr attr;
That puts the magic in the file based on endianness of the recording
system. e.g., on x86:

$ od -c perf-magic.data | head -1
0000000 E L I F F R E P h \0 \0 \0 \0 \0 \0 \0
Which means older perf binaries can't analyze new files (created with
new magic order) and newer perf binaries can't analyze older perf files
-- the new command will incorrectly want to do endian swapping on the
old file.

David


\
 
 \ /
  Last update: 2011-09-16 17:37    [from the cache]
©2003-2014 Jasper Spaans. Advertise on this site