Commit 6549a8c0 authored by Gustavo A. R. Silva's avatar Gustavo A. R. Silva Committed by Arnaldo Carvalho de Melo
Browse files

perf tools: 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.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21


[3] commit 76497732 ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: default avatarGustavo 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: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent 961224db

tools/perf/bench/sched-messaging.c

+1 −1
Original line number Diff line number Diff line
@@ -40,7 +40,7 @@ struct sender_context { 
	unsigned int num_fds;

	int ready_out;

	int wakefd;

	int out_fds[0];

	int out_fds[];

};



struct receiver_context {

tools/perf/builtin-inject.c

+1 −1
Original line number Diff line number Diff line
@@ -51,7 +51,7 @@ struct perf_inject { 
struct event_entry {

	struct list_head node;

	u32		 tid;

	union perf_event event[0];

	union perf_event event[];

};



static int output_bytes(struct perf_inject *inject, void *buf, size_t sz)

tools/perf/builtin-script.c

+1 −1
Original line number Diff line number Diff line
@@ -2449,7 +2449,7 @@ static int __cmd_script(struct perf_script *script) 
struct script_spec {

	struct list_head	node;

	struct scripting_ops	*ops;

	char			spec[0];

	char			spec[];

};



static LIST_HEAD(script_specs);

tools/perf/builtin-timechart.c

+1 −1
Original line number Diff line number Diff line
@@ -128,7 +128,7 @@ struct sample_wrapper { 
	struct sample_wrapper *next;



	u64		timestamp;

	unsigned char	data[0];

	unsigned char	data[];

};



#define TYPE_NONE	0

tools/perf/util/annotate.h

+2 −2
Original line number Diff line number Diff line
@@ -144,7 +144,7 @@ struct annotation_line { 
	u32			 idx;

	int			 idx_asm;

	int			 data_nr;

	struct annotation_data	 data[0];

	struct annotation_data	 data[];

};



struct disasm_line {
@@ -227,7 +227,7 @@ void symbol__calc_percent(struct symbol *sym, struct evsel *evsel); 
struct sym_hist {

	u64		      nr_samples;

	u64		      period;

	struct sym_hist_entry addr[0];

	struct sym_hist_entry addr[];

};



struct cyc_hist {