When decoding the perf_regs mask in regs_dump__printf(),
we loop through the mask using find_first_bit and find_next_bit functions.
"mask" is of type "u64", but sent as a "unsigned long *" to
lib functions along with sizeof(). While the exisitng code works fine in
most of the case, the logic is broken when using a 32bit perf on a
64bit kernel (Big Endian). We end up reading the wrong word of the u64
first in the lib functions. Proposed fix is to swap the words of the
u64 to handle this case. This is not endianess swap.
Suggested-by: Yury Norov <redacted>
Cc: Yury Norov <redacted>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Kan Liang <redacted>
Cc: Wang Nan <redacted>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Madhavan Srinivasan <redacted>
---
Changelog v1:
1)updated commit message and patch subject
2)Add the fix to print_sample_iregs() in builtin-script.c
tools/perf/builtin-script.c | 7 ++++++-
tools/perf/util/session.c | 7 ++++++-
2 files changed, 12 insertions(+), 2 deletions(-)
From: Jiri Olsa <hidden> Date: 2016-06-20 09:18:49
On Mon, Jun 20, 2016 at 02:14:01PM +0530, Madhavan Srinivasan wrote:
When decoding the perf_regs mask in regs_dump__printf(),
we loop through the mask using find_first_bit and find_next_bit functions.
"mask" is of type "u64", but sent as a "unsigned long *" to
lib functions along with sizeof(). While the exisitng code works fine in
most of the case, the logic is broken when using a 32bit perf on a
64bit kernel (Big Endian). We end up reading the wrong word of the u64
first in the lib functions.
hum, I still don't see why this happens.. why do we read the
wrong word in this case?
thanks,
jirka
first in the lib functions. Proposed fix is to swap the words of the
u64 to handle this case. This is not endianess swap.
On Mon, Jun 20, 2016 at 02:14:01PM +0530, Madhavan Srinivasan wrote:
quoted
When decoding the perf_regs mask in regs_dump__printf(),
we loop through the mask using find_first_bit and find_next_bit functions.
"mask" is of type "u64", but sent as a "unsigned long *" to
lib functions along with sizeof(). While the exisitng code works fine in
most of the case, the logic is broken when using a 32bit perf on a
64bit kernel (Big Endian). We end up reading the wrong word of the u64
first in the lib functions.
hum, I still don't see why this happens.. why do we read the
wrong word in this case?
If you read a u64 using (u32 *)(&val)[0] and (u32 *)(&val)[1]
you can get wrong value. This is what _find_next_bit() is doing.
In a big endian environment where 'unsigned long' is 32 bits
long, "(u32 *)(&val)[0]" gets upper 32 bits, but without this patch
perf assumes it gets lower 32 bits. The root cause is wrongly convert
u64 value to bitmap.
Thank you.
From: Jiri Olsa <hidden> Date: 2016-06-20 09:40:38
On Mon, Jun 20, 2016 at 05:27:25PM +0800, Wangnan (F) wrote:
On 2016/6/20 17:18, Jiri Olsa wrote:
quoted
On Mon, Jun 20, 2016 at 02:14:01PM +0530, Madhavan Srinivasan wrote:
quoted
When decoding the perf_regs mask in regs_dump__printf(),
we loop through the mask using find_first_bit and find_next_bit functions.
"mask" is of type "u64", but sent as a "unsigned long *" to
lib functions along with sizeof(). While the exisitng code works fine in
most of the case, the logic is broken when using a 32bit perf on a
64bit kernel (Big Endian). We end up reading the wrong word of the u64
first in the lib functions.
hum, I still don't see why this happens.. why do we read the
wrong word in this case?
If you read a u64 using (u32 *)(&val)[0] and (u32 *)(&val)[1]
you can get wrong value. This is what _find_next_bit() is doing.
In a big endian environment where 'unsigned long' is 32 bits
long, "(u32 *)(&val)[0]" gets upper 32 bits, but without this patch
perf assumes it gets lower 32 bits. The root cause is wrongly convert
u64 value to bitmap.
i see, could you please put this into comment in the code?
also we could have common function for that, to keep it on
one place only, like bitmap_from_u64 or so
thanks,
jirka
On Mon, Jun 20, 2016 at 05:27:25PM +0800, Wangnan (F) wrote:
quoted
On 2016/6/20 17:18, Jiri Olsa wrote:
quoted
On Mon, Jun 20, 2016 at 02:14:01PM +0530, Madhavan Srinivasan wrote:
quoted
When decoding the perf_regs mask in regs_dump__printf(),
we loop through the mask using find_first_bit and find_next_bit functions.
"mask" is of type "u64", but sent as a "unsigned long *" to
lib functions along with sizeof(). While the exisitng code works fine in
most of the case, the logic is broken when using a 32bit perf on a
64bit kernel (Big Endian). We end up reading the wrong word of the u64
first in the lib functions.
hum, I still don't see why this happens.. why do we read the
wrong word in this case?
If you read a u64 using (u32 *)(&val)[0] and (u32 *)(&val)[1]
you can get wrong value. This is what _find_next_bit() is doing.
Also in find_first_bit().
quoted
In a big endian environment where 'unsigned long' is 32 bits
long, "(u32 *)(&val)[0]" gets upper 32 bits, but without this patch
perf assumes it gets lower 32 bits. The root cause is wrongly convert
u64 value to bitmap.
i see, could you please put this into comment in the code?
also we could have common function for that, to keep it on
one place only, like bitmap_from_u64 or so