Commit-ID: 29dd3288705f26cc27663e79061209dabce2d5b9 Gitweb: http://git.kernel.org/tip/29dd3288705f26cc27663e79061209dabce2d5b9 Author: Madhavan Srinivasan <ma...@linux.vnet.ibm.com> AuthorDate: Wed, 17 Aug 2016 15:06:08 +0530 Committer: Ingo Molnar <mi...@kernel.org> 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 <yno...@caviumnetworks.com> Signed-off-by: Madhavan Srinivasan <ma...@linux.vnet.ibm.com> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> Reviewed-by: Yury Norov <yno...@caviumnetworks.com> Cc: Alexander Shishkin <alexander.shish...@linux.intel.com> Cc: Arnaldo Carvalho de Melo <a...@kernel.org> Cc: Arnaldo Carvalho de Melo <a...@redhat.com> Cc: Jiri Olsa <jo...@kernel.org> Cc: Jiri Olsa <jo...@redhat.com> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Michael Ellerman <m...@ellerman.id.au> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Stephane Eranian <eran...@google.com> Cc: Thomas Gleixner <t...@linutronix.de> Cc: Vince Weaver <vincent.wea...@maine.edu> Cc: linuxppc-...@lists.ozlabs.org Link: http://lkml.kernel.org/r/1471426568-31051-2-git-send-email-ma...@linux.vnet.ibm.com Signed-off-by: Ingo Molnar <mi...@kernel.org> --- 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);
