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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@caviumnetworks.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Yury Norov <ynorov@caviumnetworks.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: linuxppc-dev@lists.ozlabs.org
Link: http://lkml.kernel.org/r/1471426568-31051-2-git-send-email-maddy@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Madhavan Srinivasan 2016-08-17 15:06:08 +05:30 committed by Ingo Molnar
parent 8942c2b7f3
commit 29dd328870
2 changed files with 21 additions and 2 deletions
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18
include/linux/bitmap.h
View File

@ -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 */

5
kernel/events/core.c
View File

@ -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);