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Message-Id: <11fbc51b-6560-bebb-0aff-c9f9c51fd176@linux.vnet.ibm.com>
Date: Wed, 22 Jun 2016 09:20:43 +0530
From: Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>
To: Yury Norov <ynorov@...iumnetworks.com>
Cc: linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>,
Adrian Hunter <adrian.hunter@...el.com>,
Kan Liang <kan.liang@...el.com>,
Wang Nan <wangnan0@...wei.com>,
Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH v3] tools/perf: Fix the mask in regs_dump__printf and
print_sample_iregs
On Tuesday 21 June 2016 09:05 PM, Yury Norov wrote:
> On Tue, Jun 21, 2016 at 08:26:40PM +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).
>> When reading u64 using (u32 *)(&val)[0], perf (lib/find_*_bit()) assumes it gets
>> lower 32bits of u64 which is wrong. Proposed fix is to swap the words
>> of the u64 to handle this case. This is _not_ endianess swap.
>>
>> Suggested-by: Yury Norov <ynorov@...iumnetworks.com>
>> Cc: Yury Norov <ynorov@...iumnetworks.com>
>> Cc: Peter Zijlstra <peterz@...radead.org>
>> Cc: Ingo Molnar <mingo@...hat.com>
>> Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
>> Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
>> Cc: Jiri Olsa <jolsa@...nel.org>
>> Cc: Adrian Hunter <adrian.hunter@...el.com>
>> Cc: Kan Liang <kan.liang@...el.com>
>> Cc: Wang Nan <wangnan0@...wei.com>
>> Cc: Michael Ellerman <mpe@...erman.id.au>
>> Signed-off-by: Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>
>> ---
>> Changelog v2:
>> 1)Moved the swap code to a common function
>> 2)Added more comments in the code
>>
>> Changelog v1:
>> 1)updated commit message and patch subject
>> 2)Add the fix to print_sample_iregs() in builtin-script.c
>>
>> tools/include/linux/bitmap.h | 9 +++++++++
> What about include/linux/bitmap.h? I think we'd place it there first.
Wanted to handle that separately.
>
>> tools/perf/builtin-script.c | 16 +++++++++++++++-
>> tools/perf/util/session.c | 16 +++++++++++++++-
>> 3 files changed, 39 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/include/linux/bitmap.h b/tools/include/linux/bitmap.h
>> index 28f5493da491..79998b26eb04 100644
>> --- a/tools/include/linux/bitmap.h
>> +++ b/tools/include/linux/bitmap.h
>> @@ -2,6 +2,7 @@
>> #define _PERF_BITOPS_H
>>
>> #include <string.h>
>> +#include <limits.h>
>> #include <linux/bitops.h>
>>
>> #define DECLARE_BITMAP(name,bits) \
>> @@ -22,6 +23,14 @@ void __bitmap_or(unsigned long *dst, const unsigned long *bitmap1,
>> #define small_const_nbits(nbits) \
>> (__builtin_constant_p(nbits) && (nbits) <= BITS_PER_LONG)
>>
>> +static inline void bitmap_from_u64(unsigned long *_mask, u64 mask)
> Inline is not required. Some people don't not like it. Underscored parameter in
Not sure why you say that. IIUC we can avoid a function call overhead,
also rest of the functions in the file likes it.
> function declaration is not the best idea as well. Try:
> static void bitmap_from_u64(unsigned long *bitmap, u64 mask)
>
>> +{
>> + _mask[0] = mask & ULONG_MAX;
>> +
>> + if (sizeof(mask) > sizeof(unsigned long))
>> + _mask[1] = mask >> 32;
>> +}
>> +
>> static inline void bitmap_zero(unsigned long *dst, int nbits)
>> {
>> if (small_const_nbits(nbits))
>> diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
>> index e3ce2f34d3ad..73928310fd91 100644
>> --- a/tools/perf/builtin-script.c
>> +++ b/tools/perf/builtin-script.c
>> @@ -412,11 +412,25 @@ static void print_sample_iregs(struct perf_sample *sample,
>> struct regs_dump *regs = &sample->intr_regs;
>> uint64_t mask = attr->sample_regs_intr;
>> unsigned i = 0, r;
>> + unsigned long _mask[sizeof(mask)/sizeof(unsigned long)];
> If we start with it, I think we'd hide declaration machinery as well:
>
> #define DECLARE_L64_BITMAP(__name) unsigned long __name[sizeof(u64)/sizeof(unsigned long)]
> or
> #define L64_BITMAP_SIZE (sizeof(u64)/sizeof(unsigned long))
>
> Or both :) Whatever you prefer.
ok
>
>>
>> if (!regs)
>> return;
>>
>> - for_each_set_bit(r, (unsigned long *) &mask, sizeof(mask) * 8) {
>> + /*
>> + * Since u64 is passed as 'unsigned long *', check
>> + * to see whether we need to swap words within u64.
>> + * Reason being, in 32 bit big endian userspace on a
>> + * 64bit kernel, 'unsigned long' is 32 bits.
>> + * When reading u64 using (u32 *)(&val)[0] and (u32 *)(&val)[1],
>> + * we will get wrong value for the mask. This is what
>> + * find_first_bit() and find_next_bit() is doing.
>> + * Issue here is "(u32 *)(&val)[0]" gets upper 32 bits of u64,
>> + * but perf assumes it gets lower 32bits of u64. Hence the check
>> + * and swap.
>> + */
>> + bitmap_from_u64(_mask, mask);
>> + for_each_set_bit(r, _mask, sizeof(mask) * 8) {
>> u64 val = regs->regs[i++];
>> printf("%5s:0x%"PRIx64" ", perf_reg_name(r), val);
>> }
>> diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
>> index 5214974e841a..1337b1c73f82 100644
>> --- a/tools/perf/util/session.c
>> +++ b/tools/perf/util/session.c
>> @@ -940,8 +940,22 @@ static void branch_stack__printf(struct perf_sample *sample)
>> static void regs_dump__printf(u64 mask, u64 *regs)
>> {
>> unsigned rid, i = 0;
>> + unsigned long _mask[sizeof(mask)/sizeof(unsigned long)];
>>
>> - for_each_set_bit(rid, (unsigned long *) &mask, sizeof(mask) * 8) {
>> + /*
>> + * Since u64 is passed as 'unsigned long *', check
>> + * to see whether we need to swap words within u64.
>> + * Reason being, in 32 bit big endian userspace on a
>> + * 64bit kernel, 'unsigned long' is 32 bits.
>> + * When reading u64 using (u32 *)(&val)[0] and (u32 *)(&val)[1],
>> + * we will get wrong value for the mask. This is what
>> + * find_first_bit() and find_next_bit() is doing.
>> + * Issue here is "(u32 *)(&val)[0]" gets upper 32 bits of u64,
>> + * but perf assumes it gets lower 32bits of u64. Hence the check
>> + * and swap.
>> + */
> Identical comments... I'd prefer to see it in commit message, or
> better in function description. For me it's pretty straightforward in
> understanding what happens here in-place without comments.
I would prefer the comments here. When reading/understanding
the code, we can avoid a jump to another file :).
Maddy
>> + bitmap_from_u64(_mask, mask);
>> + for_each_set_bit(rid, _mask, sizeof(mask) * 8) {
>> u64 val = regs[i++];
>>
>> printf(".... %-5s 0x%" PRIx64 "\n",
>> --
>> 1.9.1
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