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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 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>
89 lines
2.0 KiB
C
89 lines
2.0 KiB
C
#ifndef _PERF_BRANCH_H
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#define _PERF_BRANCH_H 1
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/*
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* The linux/stddef.h isn't need here, but is needed for __always_inline used
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* in files included from uapi/linux/perf_event.h such as
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* /usr/include/linux/swab.h and /usr/include/linux/byteorder/little_endian.h,
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* detected in at least musl libc, used in Alpine Linux. -acme
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*/
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#include <stdio.h>
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#include <stdint.h>
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#include <linux/compiler.h>
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#include <linux/stddef.h>
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#include <linux/perf_event.h>
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#include <linux/types.h>
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#include "event.h"
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struct branch_flags {
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union {
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u64 value;
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struct {
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u64 mispred:1;
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u64 predicted:1;
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u64 in_tx:1;
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u64 abort:1;
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u64 cycles:16;
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u64 type:4;
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u64 reserved:40;
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};
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};
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};
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struct branch_info {
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struct addr_map_symbol from;
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struct addr_map_symbol to;
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struct branch_flags flags;
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char *srcline_from;
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char *srcline_to;
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};
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struct branch_entry {
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u64 from;
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u64 to;
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struct branch_flags flags;
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};
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struct branch_stack {
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u64 nr;
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u64 hw_idx;
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struct branch_entry entries[];
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};
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/*
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* The hw_idx is only available when PERF_SAMPLE_BRANCH_HW_INDEX is applied.
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* Otherwise, the output format of a sample with branch stack is
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* struct branch_stack {
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* u64 nr;
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* struct branch_entry entries[0];
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* }
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* Check whether the hw_idx is available,
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* and return the corresponding pointer of entries[0].
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*/
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static inline struct branch_entry *perf_sample__branch_entries(struct perf_sample *sample)
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{
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u64 *entry = (u64 *)sample->branch_stack;
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entry++;
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if (sample->no_hw_idx)
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return (struct branch_entry *)entry;
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return (struct branch_entry *)(++entry);
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}
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struct branch_type_stat {
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bool branch_to;
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u64 counts[PERF_BR_MAX];
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u64 cond_fwd;
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u64 cond_bwd;
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u64 cross_4k;
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u64 cross_2m;
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};
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void branch_type_count(struct branch_type_stat *st, struct branch_flags *flags,
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u64 from, u64 to);
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const char *branch_type_name(int type);
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void branch_type_stat_display(FILE *fp, struct branch_type_stat *st);
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int branch_type_str(struct branch_type_stat *st, char *bf, int bfsize);
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#endif /* _PERF_BRANCH_H */
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