[PATCH v3] tools/perf: Fix the mask in regs_dump__printf and print_sample_iregs

[Madhavan Srinivasan]

When decoding the perf_regs mask in regs_dump__printf(),
we loop through the mask using find_first_bit and find_next_bit functions.
"mask" is of type "u64", but sent as a "unsigned long *" to
lib functions along with sizeof().

While the exisitng code works fine in most of the case,
the logic is broken when using a 32bit perf on a 64bit kernel (Big Endian).
When reading u64 using (u32 *)(&val)[0], perf (lib/find_*_bit()) assumes it gets
lower 32bits of u64 which is wrong. Proposed fix is to swap the words
of the u64 to handle this case. This is _not_ endianess swap.

Suggested-by: Yury Norov <ynorov at caviumnetworks.com>
Cc: Yury Norov <ynorov at caviumnetworks.com>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Ingo Molnar <mingo at redhat.com>
Cc: Arnaldo Carvalho de Melo <acme at kernel.org>
Cc: Alexander Shishkin <alexander.shishkin at linux.intel.com>
Cc: Jiri Olsa <jolsa at kernel.org>
Cc: Adrian Hunter <adrian.hunter at intel.com>
Cc: Kan Liang <kan.liang at intel.com>
Cc: Wang Nan <wangnan0 at huawei.com>
Cc: Michael Ellerman <mpe at ellerman.id.au>
Signed-off-by: Madhavan Srinivasan <maddy at linux.vnet.ibm.com>
---
Changelog v2:
1)Moved the swap code to a common function
2)Added more comments in the code

Changelog v1:
1)updated commit message and patch subject
2)Add the fix to print_sample_iregs() in builtin-script.c

 tools/include/linux/bitmap.h |  9 +++++++++
 tools/perf/builtin-script.c  | 16 +++++++++++++++-
 tools/perf/util/session.c    | 16 +++++++++++++++-
 3 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/tools/include/linux/bitmap.h b/tools/include/linux/bitmap.h
index 28f5493da491..79998b26eb04 100644
--- a/tools/include/linux/bitmap.h
+++ b/tools/include/linux/bitmap.h
@@ -2,6 +2,7 @@
 #define _PERF_BITOPS_H
 
 #include <string.h>
+#include <limits.h>
 #include <linux/bitops.h>
 
 #define DECLARE_BITMAP(name,bits) \
@@ -22,6 +23,14 @@ void __bitmap_or(unsigned long *dst, const unsigned long *bitmap1,
 #define small_const_nbits(nbits) \
 	(__builtin_constant_p(nbits) && (nbits) <= BITS_PER_LONG)
 
+static inline void bitmap_from_u64(unsigned long *_mask, u64 mask)
+{
+	_mask[0] = mask & ULONG_MAX;
+
+	if (sizeof(mask) > sizeof(unsigned long))
+		_mask[1] = mask >> 32;
+}
+
 static inline void bitmap_zero(unsigned long *dst, int nbits)
 {
 	if (small_const_nbits(nbits))
diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
index e3ce2f34d3ad..73928310fd91 100644
--- a/tools/perf/builtin-script.c
+++ b/tools/perf/builtin-script.c
@@ -412,11 +412,25 @@ static void print_sample_iregs(struct perf_sample *sample,
 	struct regs_dump *regs = &sample->intr_regs;
 	uint64_t mask = attr->sample_regs_intr;
 	unsigned i = 0, r;
+	unsigned long _mask[sizeof(mask)/sizeof(unsigned long)];
 
 	if (!regs)
 		return;
 
-	for_each_set_bit(r, (unsigned long *) &mask, sizeof(mask) * 8) {
+	/*
+	 * Since u64 is passed as 'unsigned long *', check
+	 * to see whether we need to swap words within u64.
+	 * Reason being, in 32 bit big endian userspace on a
+	 * 64bit kernel, 'unsigned long' is 32 bits.
+	 * When reading u64 using (u32 *)(&val)[0] and (u32 *)(&val)[1],
+	 * we will get wrong value for the mask. This is what
+	 * find_first_bit() and find_next_bit() is doing.
+	 * Issue here is "(u32 *)(&val)[0]" gets upper 32 bits of u64,
+	 * but perf assumes it gets lower 32bits of u64. Hence the check
+	 * and swap.
+	 */
+	bitmap_from_u64(_mask, mask);
+	for_each_set_bit(r, _mask, sizeof(mask) * 8) {
 		u64 val = regs->regs[i++];
 		printf("%5s:0x%"PRIx64" ", perf_reg_name(r), val);
 	}
diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index 5214974e841a..1337b1c73f82 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -940,8 +940,22 @@ static void branch_stack__printf(struct perf_sample *sample)
 static void regs_dump__printf(u64 mask, u64 *regs)
 {
 	unsigned rid, i = 0;
+	unsigned long _mask[sizeof(mask)/sizeof(unsigned long)];
 
-	for_each_set_bit(rid, (unsigned long *) &mask, sizeof(mask) * 8) {
+	/*
+	 * Since u64 is passed as 'unsigned long *', check
+	 * to see whether we need to swap words within u64.
+	 * Reason being, in 32 bit big endian userspace on a
+	 * 64bit kernel, 'unsigned long' is 32 bits.
+	 * When reading u64 using (u32 *)(&val)[0] and (u32 *)(&val)[1],
+	 * we will get wrong value for the mask. This is what
+	 * find_first_bit() and find_next_bit() is doing.
+	 * Issue here is "(u32 *)(&val)[0]" gets upper 32 bits of u64,
+	 * but perf assumes it gets lower 32bits of u64. Hence the check
+	 * and swap.
+	 */
+	bitmap_from_u64(_mask, mask);
+	for_each_set_bit(rid, _mask, sizeof(mask) * 8) {
 		u64 val = regs[i++];
 
 		printf(".... %-5s 0x%" PRIx64 "\n",
-- 
1.9.1