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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>
78 lines
1.9 KiB
C
78 lines
1.9 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef __ORDERED_EVENTS_H
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#define __ORDERED_EVENTS_H
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#include <linux/types.h>
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struct perf_sample;
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struct ordered_event {
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u64 timestamp;
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u64 file_offset;
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union perf_event *event;
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struct list_head list;
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};
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enum oe_flush {
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OE_FLUSH__NONE,
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OE_FLUSH__FINAL,
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OE_FLUSH__ROUND,
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OE_FLUSH__HALF,
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OE_FLUSH__TOP,
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OE_FLUSH__TIME,
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};
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struct ordered_events;
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typedef int (*ordered_events__deliver_t)(struct ordered_events *oe,
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struct ordered_event *event);
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struct ordered_events_buffer {
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struct list_head list;
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struct ordered_event event[];
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};
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struct ordered_events {
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u64 last_flush;
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u64 next_flush;
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u64 max_timestamp;
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u64 max_alloc_size;
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u64 cur_alloc_size;
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struct list_head events;
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struct list_head cache;
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struct list_head to_free;
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struct ordered_events_buffer *buffer;
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struct ordered_event *last;
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ordered_events__deliver_t deliver;
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int buffer_idx;
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unsigned int nr_events;
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enum oe_flush last_flush_type;
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u32 nr_unordered_events;
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bool copy_on_queue;
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void *data;
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};
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int ordered_events__queue(struct ordered_events *oe, union perf_event *event,
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u64 timestamp, u64 file_offset);
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void ordered_events__delete(struct ordered_events *oe, struct ordered_event *event);
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int ordered_events__flush(struct ordered_events *oe, enum oe_flush how);
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int ordered_events__flush_time(struct ordered_events *oe, u64 timestamp);
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void ordered_events__init(struct ordered_events *oe, ordered_events__deliver_t deliver,
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void *data);
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void ordered_events__free(struct ordered_events *oe);
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void ordered_events__reinit(struct ordered_events *oe);
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u64 ordered_events__first_time(struct ordered_events *oe);
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static inline
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void ordered_events__set_alloc_size(struct ordered_events *oe, u64 size)
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{
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oe->max_alloc_size = size;
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}
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static inline
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void ordered_events__set_copy_on_queue(struct ordered_events *oe, bool copy)
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{
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oe->copy_on_queue = copy;
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}
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#endif /* __ORDERED_EVENTS_H */
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