When recording PEBS-via-PT, the kernel will not accept the intel_pt
event with register sampling e.g.
# perf record --kcore -c 10000 -e '{intel_pt/branch=0/,branch-loads/aux-output/ppp}' -I -- ls -l
Error:
intel_pt/branch=0/: PMU Hardware doesn't support sampling/overflow-interrupts. Try 'perf stat'
Fix by suppressing register sampling on the intel_pt evsel.
Committer notes:
Adrian informed that this is only available from Tremont onwards, so on
older processors the error continues the same as before.
Fixes: 9e64cefe43 ("perf intel-pt: Process options for PEBS event synthesis")
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Luwei Kang <luwei.kang@intel.com>
Link: http://lore.kernel.org/lkml/20200630133935.11150-2-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Commit 0a892c1c94 ("perf record: Add dummy event during system wide
synthesis") reveals an issue with Intel PT system wide tracing.
Specifically that Intel PT already adds a dummy tracking event, and it
is not the first event. Adding another dummy tracking event causes
duplicated sideband events. Fix by checking for an existing dummy
tracking event first.
Example showing duplicated switch events:
Before:
# perf record -a -e intel_pt//u uname
Linux
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.895 MB perf.data ]
# perf script --no-itrace --show-switch-events | head
swapper 0 [007] 6390.516222: PERF_RECORD_SWITCH_CPU_WIDE OUT preempt next pid/tid: 11/11
swapper 0 [007] 6390.516222: PERF_RECORD_SWITCH_CPU_WIDE OUT preempt next pid/tid: 11/11
rcu_sched 11 [007] 6390.516223: PERF_RECORD_SWITCH_CPU_WIDE IN prev pid/tid: 0/0
rcu_sched 11 [007] 6390.516224: PERF_RECORD_SWITCH_CPU_WIDE IN prev pid/tid: 0/0
rcu_sched 11 [007] 6390.516227: PERF_RECORD_SWITCH_CPU_WIDE OUT next pid/tid: 0/0
rcu_sched 11 [007] 6390.516227: PERF_RECORD_SWITCH_CPU_WIDE OUT next pid/tid: 0/0
swapper 0 [007] 6390.516228: PERF_RECORD_SWITCH_CPU_WIDE IN prev pid/tid: 11/11
swapper 0 [007] 6390.516228: PERF_RECORD_SWITCH_CPU_WIDE IN prev pid/tid: 11/11
swapper 0 [002] 6390.516415: PERF_RECORD_SWITCH_CPU_WIDE OUT preempt next pid/tid: 5556/5559
swapper 0 [002] 6390.516416: PERF_RECORD_SWITCH_CPU_WIDE OUT preempt next pid/tid: 5556/5559
After:
# perf record -a -e intel_pt//u uname
Linux
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.868 MB perf.data ]
# perf script --no-itrace --show-switch-events | head
swapper 0 [005] 6450.567013: PERF_RECORD_SWITCH_CPU_WIDE OUT preempt next pid/tid: 7179/7181
perf 7181 [005] 6450.567014: PERF_RECORD_SWITCH_CPU_WIDE IN prev pid/tid: 0/0
perf 7181 [005] 6450.567028: PERF_RECORD_SWITCH_CPU_WIDE OUT next pid/tid: 0/0
swapper 0 [005] 6450.567029: PERF_RECORD_SWITCH_CPU_WIDE IN prev pid/tid: 7179/7181
swapper 0 [005] 6450.571699: PERF_RECORD_SWITCH_CPU_WIDE OUT preempt next pid/tid: 11/11
rcu_sched 11 [005] 6450.571700: PERF_RECORD_SWITCH_CPU_WIDE IN prev pid/tid: 0/0
rcu_sched 11 [005] 6450.571702: PERF_RECORD_SWITCH_CPU_WIDE OUT next pid/tid: 0/0
swapper 0 [005] 6450.571703: PERF_RECORD_SWITCH_CPU_WIDE IN prev pid/tid: 11/11
swapper 0 [005] 6450.579703: PERF_RECORD_SWITCH_CPU_WIDE OUT preempt next pid/tid: 11/11
rcu_sched 11 [005] 6450.579704: PERF_RECORD_SWITCH_CPU_WIDE IN prev pid/tid: 0/0
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lore.kernel.org/lkml/20200629091955.17090-3-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
In the past this wasn't needed as the libaudit based code would use just
one field, and the alternative constructor would fill in all the fields,
but now that even when using the libaudit based method we need the other
fields, switch to zalloc() to make sure the other fields are zeroed at
instantiation time.
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
When we moved to a syscalltbl generated from the kernel syscall tables
(arch/..../syscall*.tbl) the idea was to either use it, when having the
generator (e.g. tools/perf/arch/x86/entry/syscalls/syscalltbl.sh), or
falling back to the previous audit-libs based way of mapping syscall ids
to strings and the other way around.
At first we just needed the audit_detect_machine() return to then use it
to the str->id/id->str, or the other fields for the now used by default
in the most well developed arches method of using the syscall table
generator.
The problem is that then the libaudit code fell into disrepair, and
architectures where it is the method used are not working.
Now, with NO_SYSCALL_TABLE=1 being possible to pass on the make command
line we can automate the testing of that method even on x86-64, arm64,
etc.
And doing it I noted that we actually use fields in both entries in the
union, oops, so ditch the union, as we need all those fields at the same
time.
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Context switch events are added automatically by Intel PT and Coresight.
Make it possible to suppress them. That is useful for tracing the
scheduler without the disturbance that the switch event processing
creates.
Example:
Prerequisites:
$ which perf
~/bin/perf
$ sudo setcap "cap_sys_rawio,cap_sys_admin,cap_sys_ptrace,cap_syslog,cap_ipc_lock=ep" ~/bin/perf
$ sudo chmod +r /proc/kcore
Before:
$ perf record --no-switch-events --kcore -a -e intel_pt//k -- sleep 0.001
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.938 MB perf.data ]
$ perf script -D | grep PERF_RECORD_SWITCH | wc -l
572
After:
$ perf record --no-switch-events --kcore -a -e intel_pt//k -- sleep 0.001
Warning:
Intel Processor Trace decoding will not be possible except for kernel tracing!
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.838 MB perf.data ]
$ perf script -D | grep PERF_RECORD_SWITCH | wc -l
0
$ sudo chmod go-r /proc/kcore
$ sudo setcap -r ~/bin/perf
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: http://lore.kernel.org/lkml/20200528120859.21604-1-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
For a Java method signature like:
Ljava/lang/AbstractStringBuilder;appendChars(Ljava/lang/String;II)V
The demangler produces:
void class java.lang.AbstractStringBuilder.appendChars(class java.lang., shorttring., int, int)
The arguments should be (java.lang.String, int, int) but the demangler
interprets the "S" in String as the type code for "short". Correct this
and two other minor things:
- There is no "bool" type in Java, should be "boolean".
- The demangler prepends "class" to every Java class name. This is not
standard Java syntax and it wastes a lot of horizontal space if the
signature is long. Remove this as there isn't any ambiguity between
class names and primitives.
Committer notes:
This was split from a larger patch that also added a java demangler
'perf test' entry, that, before this patch shows the error being fixed
by it:
$ perf test java
65: Demangle Java : FAILED!
$ perf test -v java
Couldn't bump rlimit(MEMLOCK), failures may take place when creating BPF maps, etc
65: Demangle Java :
--- start ---
test child forked, pid 307264
FAILED: Ljava/lang/StringLatin1;equals([B[B)Z: bool class java.lang.StringLatin1.equals(byte[], byte[]) != boolean java.lang.StringLatin1.equals(byte[], byte[])
FAILED: Ljava/util/zip/ZipUtils;CENSIZ([BI)J: long class java.util.zip.ZipUtils.CENSIZ(byte[], int) != long java.util.zip.ZipUtils.CENSIZ(byte[], int)
FAILED: Ljava/util/regex/Pattern$BmpCharProperty;match(Ljava/util/regex/Matcher;ILjava/lang/CharSequence;)Z: bool class java.util.regex.Pattern$BmpCharProperty.match(class java.util.regex.Matcher., int, class java.lang., charhar, shortequence) != boolean java.util.regex.Pattern$BmpCharProperty.match(java.util.regex.Matcher, int, java.lang.CharSequence)
FAILED: Ljava/lang/AbstractStringBuilder;appendChars(Ljava/lang/String;II)V: void class java.lang.AbstractStringBuilder.appendChars(class java.lang., shorttring., int, int) != void java.lang.AbstractStringBuilder.appendChars(java.lang.String, int, int)
FAILED: Ljava/lang/Object;<init>()V: void class java.lang.Object<init>() != void java.lang.Object<init>()
test child finished with -1
---- end ----
Demangle Java: FAILED!
$
After applying this patch:
$ perf test java
65: Demangle Java : Ok
$
Signed-off-by: Nick Gasson <nick.gasson@arm.com>
Reviewed-by: Ian Rogers <irogers@google.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Tested-by: Ian Rogers <irogers@google.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20200427061520.24905-4-nick.gasson@arm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
A metric group contains multiple metrics. These metrics may use the same
events. If metrics use separate events then it leads to more
multiplexing and overall metric counts fail to sum to 100%.
Modify how metrics are associated with events so that if the events in
an earlier group satisfy the current metric, the same events are used.
A record of used events is kept and at the end of processing unnecessary
events are eliminated.
Before:
$ perf stat -a -M TopDownL1 sleep 1
Performance counter stats for 'system wide':
920,211,343 uops_issued.any # 0.5 Backend_Bound (16.56%)
1,977,733,128 idq_uops_not_delivered.core (16.56%)
51,668,510 int_misc.recovery_cycles (16.56%)
732,305,692 uops_retired.retire_slots (16.56%)
1,497,621,849 cycles (16.56%)
721,098,274 uops_issued.any # 0.1 Bad_Speculation (16.79%)
1,332,681,791 cycles (16.79%)
552,475,482 uops_retired.retire_slots (16.79%)
47,708,340 int_misc.recovery_cycles (16.79%)
1,383,713,292 cycles
# 0.4 Frontend_Bound (16.76%)
2,013,757,701 idq_uops_not_delivered.core (16.76%)
1,373,363,790 cycles
# 0.1 Retiring (33.54%)
577,302,589 uops_retired.retire_slots (33.54%)
392,766,987 inst_retired.any # 0.3 IPC (50.24%)
1,351,873,350 cpu_clk_unhalted.thread (50.24%)
1,332,510,318 cycles
# 5330041272.0 SLOTS (49.90%)
1.006336145 seconds time elapsed
After:
$ perf stat -a -M TopDownL1 sleep 1
Performance counter stats for 'system wide':
765,949,145 uops_issued.any # 0.1 Bad_Speculation
# 0.5 Backend_Bound (50.09%)
1,883,830,591 idq_uops_not_delivered.core # 0.3 Frontend_Bound (50.09%)
48,237,080 int_misc.recovery_cycles (50.09%)
581,798,385 uops_retired.retire_slots # 0.1 Retiring (50.09%)
1,361,628,527 cycles
# 5446514108.0 SLOTS (50.09%)
391,415,714 inst_retired.any # 0.3 IPC (49.91%)
1,336,486,781 cpu_clk_unhalted.thread (49.91%)
1.005469298 seconds time elapsed
Note: Bad_Speculation + Backend_Bound + Frontend_Bound + Retiring = 100%
after, where as before it is 110%. After there are 2 groups, whereas
before there are 6. After the cycles event appears once, before it
appeared 5 times.
Signed-off-by: Ian Rogers <irogers@google.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Andrii Nakryiko <andriin@fb.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Jin Yao <yao.jin@linux.intel.com>
Cc: John Garry <john.garry@huawei.com>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Kim Phillips <kim.phillips@amd.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Clarke <pc@us.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: bpf@vger.kernel.org
Cc: netdev@vger.kernel.org
Link: http://lore.kernel.org/lkml/20200520182011.32236-6-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array
member[1][2], introduced in C99:
struct foo {
int stuff;
struct boo array[];
};
By making use of the mechanism above, we will get a compiler warning in
case the flexible array does not occur last in the structure, which will
help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.
Also, notice that, dynamic memory allocations won't be affected by this
change:
"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]
sizeof(flexible-array-member) triggers a warning because flexible array
members have incomplete type[1]. There are some instances of code in
which the sizeof operator is being incorrectly/erroneously applied to
zero-length arrays and the result is zero. Such instances may be hiding
some bugs. So, this work (flexible-array member conversions) will also
help to get completely rid of those sorts of issues.
This issue was found with the help of Coccinelle and audited _manually_.
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 7649773293 ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Gustavo A. R. Silva <gustavo@embeddedor.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20200520191613.GA26869@embeddedor
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Add support for new "stat.big-num" boolean option.
This allows a user to set a default for "--no-big-num" for "perf stat"
commands.
--
$ perf config stat.big-num
$ perf stat --event cycles /bin/true
Performance counter stats for '/bin/true':
778,849 cycles
[...]
$ perf config stat.big-num=false
$ perf config stat.big-num
stat.big-num=false
$ perf stat --event cycles /bin/true
Performance counter stats for '/bin/true':
769622 cycles
[...]
--
There is an interaction with "--field-separator" that must be
accommodated, such that specifying "--big-num --field-separator={x}"
still reports an invalid combination of options.
Documentation for perf-config and perf-stat updated.
Signed-off-by: Paul Clarke <pc@us.ibm.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Link: http://lore.kernel.org/lkml/1589991815-17951-1-git-send-email-pc@us.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
key_scan_pos is a pointer for getting scan position in
bpf__obj_config_map() for each BPF map configuration term,
but it's misused when error not happened.
Committer notes:
The point is that the only user of this is:
tools/perf/util/parse-events.c
err = bpf__config_obj(obj, term, parse_state->evlist, &error_pos);
if (err) bpf__strerror_config_obj(obj, term, parse_state->evlist, &error_pos, err, errbuf, sizeof(errbuf));
And then:
int bpf__strerror_config_obj(struct bpf_object *obj __maybe_unused,
struct parse_events_term *term __maybe_unused,
struct evlist *evlist __maybe_unused,
int *error_pos __maybe_unused, int err,
char *buf, size_t size)
{
bpf__strerror_head(err, buf, size);
bpf__strerror_entry(BPF_LOADER_ERRNO__OBJCONF_MAP_TYPE,
"Can't use this config term with this map type");
bpf__strerror_end(buf, size);
return 0;
}
So this is infrastructure that Wang Nan put in place for providing
better error messages but that he ended up not using, so I'll apply the
fix, its correct even not fixing any real problem at this time.
Fixes: 066dacbf2a ("perf bpf: Add API to set values to map entries in a bpf object")
Signed-off-by: Wang ShaoBo <bobo.shaobowang@huawei.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Cheng Jian <cj.chengjian@huawei.com>
Cc: Hanjun Guo <guohanjun@huawei.com>
Cc: Li Bin <huawei.libin@huawei.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Wang Nan <wangnan0@huawei.com>
Cc: Xie XiuQi <xiexiuqi@huawei.com>
Cc: bpf@vger.kernel.org
Link: http://lore.kernel.org/lkml/20200520033216.48310-1-bobo.shaobowang@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
To collect the overall statistics for interval mode, we copy the counts
from evsel->prev_raw_counts to evsel->counts.
For AGGR_GLOBAL mode, because the perf_stat_process_counter creates aggr
values from per cpu values, but the per cpu values are 0, so the
calculated aggr values will be always 0.
This patch uses a trick that saves the previous aggr value to the first
member of perf_counts, then aggr calculation in process_counter_values
can work correctly for AGGR_GLOBAL.
v6:
---
Add comments in perf_evlist__save_aggr_prev_raw_counts.
Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
Reviewed-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jin Yao <yao.jin@intel.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20200520042737.24160-5-yao.jin@linux.intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
It would be useful to support the overall statistics for perf-stat
interval mode. For example, report the summary at the end of "perf-stat
-I" output.
But since perf-stat can support many aggregation modes, such as
--per-thread, --per-socket, -M and etc, we need a solution which doesn't
bring much complexity.
The idea is to use 'evsel->prev_raw_counts' which is updated in each
interval and it's saved with the latest counts. Before reporting the
summary, we copy the counts from evsel->prev_raw_counts to
evsel->counts, and next we just follow non-interval processing.
v5:
---
Don't save the previous aggr value to the member of [cpu0,thread0]
in perf_counts. Originally that was a trick because the
perf_stat_process_counter would create aggr values from per cpu
values. But we don't need to do that all the time. We will
handle it in next patch.
Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
Reviewed-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jin Yao <yao.jin@intel.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20200520042737.24160-4-yao.jin@linux.intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Metrics like UNC_M_POWER_SELF_REFRESH encode 100 as "100." and
consequently the 100 is treated as a symbol. Alter the regular
expression to allow the dot to be before or after the number.
Note, this passed the pmu-events test as that tests the validity of a
number using strtod rather than lex code. strtod allows the dot after.
Add a test for this behavior.
Fixes: 26226a9772 (perf expr: Move expr lexer to flex)
Signed-off-by: Ian Rogers <irogers@google.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: John Garry <john.garry@huawei.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Clarke <pc@us.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Ian reported that we allow to parse following:
$ perf stat -e ,cycles true
which is wrong and we should fail, like we do with this fix:
$ perf stat -e ,cycles true
event syntax error: ',cycles'
\___ parser error
The reason is that we don't have rule for ',' in 'event' start condition
and it's matched and accepted by default rule.
Add scanner debug support (that Ian already added for expr code),
which was really useful for finding this. It's enabled together with
bison debug via 'make PARSER_DEBUG=1'.
Reported-by: Ian Rogers <irogers@google.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Ian Rogers <irogers@google.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20200520074050.156988-1-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array
member[1][2], introduced in C99:
struct foo {
int stuff;
struct boo array[];
};
By making use of the mechanism above, we will get a compiler warning in
case the flexible array does not occur last in the structure, which will
help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.
Also, notice that, dynamic memory allocations won't be affected by this
change:
"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]
sizeof(flexible-array-member) triggers a warning because flexible array
members have incomplete type[1]. There are some instances of code in
which the sizeof operator is being incorrectly/erroneously applied to
zero-length arrays and the result is zero. Such instances may be hiding
some bugs. So, this work (flexible-array member conversions) will also
help to get completely rid of those sorts of issues.
This issue was found with the help of Coccinelle.
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 7649773293 ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Gustavo A. R. Silva <gustavo@embeddedor.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20200515172926.GA31976@embeddedor
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
