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Message-ID: <20160621153531.GA32361@yury-N73SV>
Date: Tue, 21 Jun 2016 18:35:31 +0300
From: Yury Norov <ynorov@...iumnetworks.com>
To: Madhavan Srinivasan <maddy@...ux.vnet.ibm.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 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.
> 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
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.
>
> 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.
> + 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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