Commit-ID: 29dd3288705f26cc27663e79061209dabce2d5b9
Gitweb: http://git.kernel.org/tip/29dd3288705f26cc27663e79061209dabce2d5b9
Author: Madhavan Srinivasan <maddy@xxxxxxxxxxxxxxxxxx>
AuthorDate: Wed, 17 Aug 2016 15:06:08 +0530
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 18 Aug 2016 10:44:20 +0200
bitmap.h, perf/core: Fix the mask in perf_output_sample_regs()
When decoding the perf_regs mask in perf_output_sample_regs(),
we loop through the mask using find_first_bit and find_next_bit functions.
While the exisiting code works fine in most of the case, the logic
is broken for big-endian 32-bit kernels.
When reading a u64 mask using (u32 *)(&val)[0], find_*_bit() assumes
that it gets the lower 32 bits of u64, but instead it gets the upper
32 bits - which is wrong.
The fix is to swap the words of the u64 to handle this case.
This is _not_ a regular endianness swap.
Suggested-by: Yury Norov <ynorov@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Madhavan Srinivasan <maddy@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Yury Norov <ynorov@xxxxxxxxxxxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Vince Weaver <vincent.weaver@xxxxxxxxx>
Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/1471426568-31051-2-git-send-email-maddy@xxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
include/linux/bitmap.h | 18 ++++++++++++++++++
kernel/events/core.c | 5 +++--
2 files changed, 21 insertions(+), 2 deletions(-)
diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 598bc99..3b77588 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -339,6 +339,24 @@ static inline int bitmap_parse(const char *buf, unsigned int buflen,
return __bitmap_parse(buf, buflen, 0, maskp, nmaskbits);
}
+/*
+ * bitmap_from_u64 - Check and swap words within u64.
+ * @mask: source bitmap
+ * @dst: destination bitmap
+ *
+ * In 32-bit Big Endian kernel, when using (u32 *)(&val)[*]
+ * to read u64 mask, we will get the wrong word.
+ * That is "(u32 *)(&val)[0]" gets the upper 32 bits,
+ * but we expect the lower 32-bits of u64.
+ */
+static inline void bitmap_from_u64(unsigned long *dst, u64 mask)
+{
+ dst[0] = mask & ULONG_MAX;
+
+ if (sizeof(mask) > sizeof(unsigned long))
+ dst[1] = mask >> 32;
+}
+
#endif /* __ASSEMBLY__ */
#endif /* __LINUX_BITMAP_H */
diff --git a/kernel/events/core.c b/kernel/events/core.c
index ca4fde5..849919c 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5340,9 +5340,10 @@ perf_output_sample_regs(struct perf_output_handle *handle,
struct pt_regs *regs, u64 mask)
{
int bit;
+ DECLARE_BITMAP(_mask, 64);
- for_each_set_bit(bit, (const unsigned long *) &mask,
- sizeof(mask) * BITS_PER_BYTE) {
+ bitmap_from_u64(_mask, mask);
+ for_each_set_bit(bit, _mask, sizeof(mask) * BITS_PER_BYTE) {
u64 val;
val = perf_reg_value(regs, bit);
--
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