Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 29dd3288 authored by Madhavan Srinivasan's avatar Madhavan Srinivasan Committed by Ingo Molnar
Browse files

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: default avatarYury Norov <ynorov@caviumnetworks.com>
Signed-off-by: default avatarMadhavan Srinivasan <maddy@linux.vnet.ibm.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarYury 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: default avatarIngo Molnar <mingo@kernel.org>
parent 8942c2b7

include/linux/bitmap.h

+18 −0
Original line number Diff line number Diff line
@@ -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 */

kernel/events/core.c

+3 −2
Original line number Diff line number Diff line
@@ -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);