linux-kernel - [PATCH 5/5] perf, tool: Fix endianity trick for adds

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Date:	Mon,  7 May 2012 13:29:09 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	acme@...hat.com, a.p.zijlstra@...llo.nl, mingo@...e.hu,
	paulus@...ba.org, cjashfor@...ux.vnet.ibm.com, fweisbec@...il.com
Cc:	linux-kernel@...r.kernel.org, dsahern@...il.com,
	Jiri Olsa <jolsa@...hat.com>
Subject: [PATCH 5/5] perf, tool: Fix endianity trick for adds_features bitmask

Addons bitmask is stored as array of unsigned long values. The size
of the unsigned long is same as pointer size for architecture, so it
could differ for each architecture.

To handle the endianity for adds_features bitmask, we first swap the
bitmaks as u64 values and check for HEADER_HOSTNAME bit. If not set we
want to unswap the u64 values and swap the adds_features as u32 values.

This is currently buggy, since we swap just first 32bits of each u64
value. Adding swap of the next 32 bits as well.  Also adding & using
BITS_TO_U64 instead of BITS_TO_LONGS as counter max due to the different
size of unsigned longs per architecture.

Note, running following to test perf endianity handling:
  - origin system:
    # perf record -a -- sleep 10 (any perf record will do)
    # perf report > report.origin
    # perf archive perf.data

  - copy the perf.data, report.origin and perf.data.tar.bz2
    to a target system and run:
    # tar xjvf perf.data.tar.bz2 -C ~/.debug
    # perf report > report.target
    # diff -u report.origin report.target

  - the diff should produce no output
    (besides some white space stuff and possibly different
     date/TZ output)

Signed-off-by: Jiri Olsa <jolsa@...hat.com>
---
 tools/perf/util/header.c               |   20 +++++++++++++++-----
 tools/perf/util/include/linux/bitops.h |    1 +
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index c0b70c6..a56db7e 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -1963,13 +1963,23 @@ int perf_file_header__read(struct perf_file_header *header,
 		 * file), punt and fallback to the original behavior --
 		 * clearing all feature bits and setting buildid.
 		 */
-		for (i = 0; i < BITS_TO_LONGS(HEADER_FEAT_BITS); ++i)
-			header->adds_features[i] = bswap_64(header->adds_features[i]);
+
+		mem_bswap_64(&header->adds_features,
+			     BITS_TO_U64(HEADER_FEAT_BITS));
 
 		if (!test_bit(HEADER_HOSTNAME, header->adds_features)) {
-			for (i = 0; i < BITS_TO_LONGS(HEADER_FEAT_BITS); ++i) {
-				header->adds_features[i] = bswap_64(header->adds_features[i]);
-				header->adds_features[i] = bswap_32(header->adds_features[i]);
+			u64 *v = (u64 *) &header->adds_features;
+
+			for (i = 0; i < BITS_TO_U64(HEADER_FEAT_BITS); ++i) {
+				union {
+					u64 val64;
+					u32 val32[2];
+				} u;
+
+				u.val64 = *v++;
+				u.val64 = bswap_64(u.val64);
+				u.val32[0] = bswap_32(u.val32[0]);
+				u.val32[1] = bswap_32(u.val32[1]);
 			}
 		}
 
diff --git a/tools/perf/util/include/linux/bitops.h b/tools/perf/util/include/linux/bitops.h
index f1584833..10096cb 100644
--- a/tools/perf/util/include/linux/bitops.h
+++ b/tools/perf/util/include/linux/bitops.h
@@ -8,6 +8,7 @@
 #define BITS_PER_LONG __WORDSIZE
 #define BITS_PER_BYTE           8
 #define BITS_TO_LONGS(nr)       DIV_ROUND_UP(nr, BITS_PER_BYTE * sizeof(long))
+#define BITS_TO_U64(nr)         DIV_ROUND_UP(nr, BITS_PER_BYTE * sizeof(u64))
 
 #define for_each_set_bit(bit, addr, size) \
 	for ((bit) = find_first_bit((addr), (size));		\
-- 
1.7.7.6

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