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linux-next/tools/perf/util/branch.h
Gustavo A. R. Silva ffe7428e6d perf branch: Replace zero-length array with flexible-array
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>
2020-05-28 10:03:27 -03:00

89 lines
2.0 KiB
C

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