From: Arnaldo Carvalho de Melo <acme@kernel.org>
To: Ian Rogers <irogers@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@kernel.org>, Namhyung Kim <namhyung@kernel.org>,
James Clark <james.clark@arm.com>,
Kees Cook <keescook@chromium.org>,
"Gustavo A. R. Silva" <gustavoars@kernel.org>,
Adrian Hunter <adrian.hunter@intel.com>,
Riccardo Mancini <rickyman7@gmail.com>,
German Gomez <german.gomez@arm.com>,
Colin Ian King <colin.king@intel.com>,
Song Liu <songliubraving@fb.com>,
Dave Marchevsky <davemarchevsky@fb.com>,
Athira Rajeev <atrajeev@linux.vnet.ibm.com>,
Alexey Bayduraev <alexey.v.bayduraev@linux.intel.com>,
Leo Yan <leo.yan@linaro.org>,
linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
Stephane Eranian <eranian@google.com>
Subject: Re: [PATCH v2 4/6] perf cpumap: Fix alignment for masks in event encoding
Date: Fri, 19 Aug 2022 12:58:35 -0300 [thread overview]
Message-ID: <Yv+zK8UxUAP83zkp@kernel.org> (raw)
In-Reply-To: <Yv60COAP90TEiWkx@kernel.org>
Em Thu, Aug 18, 2022 at 06:50:00PM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Tue, Jun 14, 2022 at 07:33:51AM -0700, Ian Rogers escreveu:
> > A mask encoding of a cpu map is laid out as:
> > u16 nr
> > u16 long_size
> > unsigned long mask[];
> > However, the mask may be 8-byte aligned meaning there is a 4-byte pad
> > after long_size. This means 32-bit and 64-bit builds see the mask as
> > being at different offsets. On top of this the structure is in the byte
> > data[] encoded as:
> > u16 type
> > char data[]
> > This means the mask's struct isn't the required 4 or 8 byte aligned, but
> > is offset by 2. Consequently the long reads and writes are causing
> > undefined behavior as the alignment is broken.
> >
> > Fix the mask struct by creating explicit 32 and 64-bit variants, use a
> > union to avoid data[] and casts; the struct must be packed so the
> > layout matches the existing perf.data layout. Taking an address of a
> > member of a packed struct breaks alignment so pass the packed
> > perf_record_cpu_map_data to functions, so they can access variables with
> > the right alignment.
> >
> > As the 64-bit version has 4 bytes of padding, optimizing writing to only
> > write the 32-bit version.
> >
> > Signed-off-by: Ian Rogers <irogers@google.com>
> > ---
> > tools/lib/perf/include/perf/event.h | 36 +++++++++++--
> > tools/perf/tests/cpumap.c | 19 ++++---
> > tools/perf/util/cpumap.c | 80 +++++++++++++++++++++++------
> > tools/perf/util/cpumap.h | 4 +-
> > tools/perf/util/session.c | 30 +++++------
> > tools/perf/util/synthetic-events.c | 34 +++++++-----
> > 6 files changed, 143 insertions(+), 60 deletions(-)
> >
> > diff --git a/tools/lib/perf/include/perf/event.h b/tools/lib/perf/include/perf/event.h
> > index e7758707cadd..d2d32589758a 100644
> > --- a/tools/lib/perf/include/perf/event.h
> > +++ b/tools/lib/perf/include/perf/event.h
> > @@ -6,6 +6,7 @@
> > #include <linux/types.h>
> > #include <linux/limits.h>
> > #include <linux/bpf.h>
> > +#include <linux/compiler.h>
> > #include <sys/types.h> /* pid_t */
> >
> > #define event_contains(obj, mem) ((obj).header.size > offsetof(typeof(obj), mem))
> > @@ -153,20 +154,47 @@ enum {
> > PERF_CPU_MAP__MASK = 1,
> > };
> >
> > +/*
> > + * Array encoding of a perf_cpu_map where nr is the number of entries in cpu[]
> > + * and each entry is a value for a CPU in the map.
> > + */
> > struct cpu_map_entries {
> > __u16 nr;
> > __u16 cpu[];
> > };
> >
> > -struct perf_record_record_cpu_map {
> > +/* Bitmap encoding of a perf_cpu_map where bitmap entries are 32-bit. */
> > +struct perf_record_mask_cpu_map32 {
> > + /* Number of mask values. */
> > __u16 nr;
> > + /* Constant 4. */
> > __u16 long_size;
> > - unsigned long mask[];
> > + /* Bitmap data. */
> > + __u32 mask[];
> > };
> >
> > -struct perf_record_cpu_map_data {
> > +/* Bitmap encoding of a perf_cpu_map where bitmap entries are 64-bit. */
> > +struct perf_record_mask_cpu_map64 {
> > + /* Number of mask values. */
> > + __u16 nr;
> > + /* Constant 8. */
> > + __u16 long_size;
> > + /* Legacy padding. */
> > + char __pad[4];
> > + /* Bitmap data. */
> > + __u64 mask[];
> > +};
> > +
> > +struct __packed perf_record_cpu_map_data {
>
> In various places I'm getting this:
>
> [perfbuilder@five x-riscv]$ export BUILD_TARBALL=http://192.168.86.14/perf/perf-6.0.0-rc1.tar.xz
> [perfbuilder@five x-riscv]$ time dm .
> 1 5.47 ubuntu:22.04-x-riscv64 : FAIL gcc version 11.2.0 (Ubuntu 11.2.0-16ubuntu1)
> In file included from mmap.c:10:
> /git/perf-6.0.0-rc1/tools/lib/perf/include/perf/event.h:190:34: error: packed attribute causes inefficient alignment for 'type' [-Werror=attributes]
> 190 | __u16 type;
> | ^~~~
> cc1: all warnings being treated as errors
> In file included from util/event.h:12,
> from builtin-diff.c:12:
> /git/perf-6.0.0-rc1/tools/lib/perf/include/perf/event.h:190:34: error: packed attribute causes inefficient alignment for 'type' [-Werror=attributes]
> 190 | __u16 type;
> | ^~~~
> In file included from util/events_stats.h:6,
> from util/evlist.h:12,
> from builtin-evlist.c:11:
> /git/perf-6.0.0-rc1/tools/lib/perf/include/perf/event.h:190:34: error: packed attribute causes inefficient alignment for 'type' [-Werror=attributes]
> 190 | __u16 type;
> | ^~~~
>
> So probably we need to disable this -Werror=attributes in some
> architectures?
Slapped this there:
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wpacked"
#pragma GCC diagnostic ignored "-Wattributes"
struct __packed perf_record_cpu_map_data {
__u16 type;
union {
/* Used when type == PERF_CPU_MAP__CPUS. */
struct cpu_map_entries cpus_data;
/* Used when type == PERF_CPU_MAP__MASK and long_size == 4. */
struct perf_record_mask_cpu_map32 mask32_data;
/* Used when type == PERF_CPU_MAP__MASK and long_size == 8. */
struct perf_record_mask_cpu_map64 mask64_data;
};
};
#pragma GCC diagnostic pop
next prev parent reply other threads:[~2022-08-19 16:18 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-14 14:33 [PATCH v2 0/6] Corrections to cpu map event encoding Ian Rogers
2022-06-14 14:33 ` [PATCH v2 1/6] perf cpumap: Const map for max Ian Rogers
2022-06-14 14:33 ` [PATCH v2 2/6] perf cpumap: Synthetic events and const/static Ian Rogers
2022-06-14 14:33 ` [PATCH v2 3/6] perf cpumap: Compute mask size in constant time Ian Rogers
2022-06-14 14:33 ` [PATCH v2 4/6] perf cpumap: Fix alignment for masks in event encoding Ian Rogers
2022-06-14 22:44 ` Namhyung Kim
2022-06-14 23:51 ` Ian Rogers
2022-06-29 9:18 ` Jiri Olsa
2022-06-29 16:05 ` Ian Rogers
2022-08-18 21:50 ` Arnaldo Carvalho de Melo
2022-08-18 22:49 ` Ian Rogers
2022-08-19 15:58 ` Arnaldo Carvalho de Melo [this message]
2022-08-19 17:09 ` Ian Rogers
2022-08-19 17:28 ` Arnaldo Carvalho de Melo
2022-08-26 12:57 ` Alexander Gordeev
2022-08-26 16:20 ` Ian Rogers
2022-06-14 14:33 ` [PATCH v2 5/6] perf events: Prefer union over variable length array Ian Rogers
2022-06-14 14:33 ` [PATCH v2 6/6] perf cpumap: Add range data encoding Ian Rogers
2022-06-29 9:31 ` Jiri Olsa
2022-06-29 16:19 ` Ian Rogers
2022-07-31 12:39 ` Jiri Olsa
2022-08-04 19:30 ` Ian Rogers
2022-09-07 22:41 ` Ian Rogers
2022-09-07 23:47 ` Arnaldo Carvalho de Melo
2022-09-08 18:52 ` Arnaldo Carvalho de Melo
2022-07-15 17:01 ` [PATCH v2 0/6] Corrections to cpu map event encoding Ian Rogers
2022-07-29 2:01 ` Ian Rogers
2022-07-29 11:35 ` Jiri Olsa
2022-07-29 14:28 ` Ian Rogers
2022-07-31 12:37 ` Jiri Olsa
2022-08-04 20:23 ` Jiri Olsa
[not found] ` <CAP-5=fX-Ex1uv0hxCwDkkAyFV6VQNPRB5uSPpCDNgqu5ZV=bCA@mail.gmail.com>
2022-08-16 19:51 ` Arnaldo Carvalho de Melo
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