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>
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 @@
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 */
