Message-ID: <20200507190615.GA15677@embeddedor>
Date:   Thu, 7 May 2020 14:06:15 -0500
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] perf script: 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 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
---
 arch/x86/events/intel/bts.c              |    2 +-
 arch/x86/events/intel/uncore.h           |    2 +-
 include/linux/perf_event.h               |    4 ++--
 kernel/events/callchain.c                |    2 +-
 kernel/events/internal.h                 |    2 +-
 tools/perf/bench/sched-messaging.c       |    2 +-
 tools/perf/builtin-inject.c              |    2 +-
 tools/perf/builtin-script.c              |    2 +-
 tools/perf/builtin-timechart.c           |    2 +-
 tools/perf/util/annotate.h               |    4 ++--
 tools/perf/util/branch.h                 |    2 +-
 tools/perf/util/cputopo.h                |    2 +-
 tools/perf/util/dso.h                    |    4 ++--
 tools/perf/util/event.h                  |    2 +-
 tools/perf/util/jitdump.c                |    2 +-
 tools/perf/util/jitdump.h                |    6 +++---
 tools/perf/util/ordered-events.h         |    2 +-
 tools/perf/util/pstack.c                 |    2 +-
 tools/perf/util/symbol.h                 |    2 +-
 tools/perf/util/unwind-libunwind-local.c |    2 +-
 20 files changed, 25 insertions(+), 25 deletions(-)

diff --git a/arch/x86/events/intel/bts.c b/arch/x86/events/intel/bts.c
index 6a3b599ee0fe..731dd8d0dbb1 100644
--- a/arch/x86/events/intel/bts.c
+++ b/arch/x86/events/intel/bts.c
@@ -58,7 +58,7 @@ struct bts_buffer {
 	local_t		head;
 	unsigned long	end;
 	void		**data_pages;
-	struct bts_phys	buf[0];
+	struct bts_phys	buf[];
 };
 
 static struct pmu bts_pmu;
diff --git a/arch/x86/events/intel/uncore.h b/arch/x86/events/intel/uncore.h
index 0da4a4605536..b469ddd45515 100644
--- a/arch/x86/events/intel/uncore.h
+++ b/arch/x86/events/intel/uncore.h
@@ -130,7 +130,7 @@ struct intel_uncore_box {
 	struct list_head list;
 	struct list_head active_list;
 	void __iomem *io_addr;
-	struct intel_uncore_extra_reg shared_regs[0];
+	struct intel_uncore_extra_reg shared_regs[];
 };
 
 /* CFL uncore 8th cbox MSRs */
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 9c3e7619c929..306b07b56cc6 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -61,7 +61,7 @@ struct perf_guest_info_callbacks {
 
 struct perf_callchain_entry {
 	__u64				nr;
-	__u64				ip[0]; /* /proc/sys/kernel/perf_event_max_stack */
+	__u64				ip[]; /* /proc/sys/kernel/perf_event_max_stack */
 };
 
 struct perf_callchain_entry_ctx {
@@ -113,7 +113,7 @@ struct perf_raw_record {
 struct perf_branch_stack {
 	__u64				nr;
 	__u64				hw_idx;
-	struct perf_branch_entry	entries[0];
+	struct perf_branch_entry	entries[];
 };
 
 struct task_struct;
diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
index c2b41a263166..b1991043b7d8 100644
--- a/kernel/events/callchain.c
+++ b/kernel/events/callchain.c
@@ -16,7 +16,7 @@
 
 struct callchain_cpus_entries {
 	struct rcu_head			rcu_head;
-	struct perf_callchain_entry	*cpu_entries[0];
+	struct perf_callchain_entry	*cpu_entries[];
 };
 
 int sysctl_perf_event_max_stack __read_mostly = PERF_MAX_STACK_DEPTH;
diff --git a/kernel/events/internal.h b/kernel/events/internal.h
index f16f66b6b655..fcbf5616a441 100644
--- a/kernel/events/internal.h
+++ b/kernel/events/internal.h
@@ -55,7 +55,7 @@ struct perf_buffer {
 	void				*aux_priv;
 
 	struct perf_event_mmap_page	*user_page;
-	void				*data_pages[0];
+	void				*data_pages[];
 };
 
 extern void rb_free(struct perf_buffer *rb);
diff --git a/tools/perf/bench/sched-messaging.c b/tools/perf/bench/sched-messaging.c
index 97e4a4fb3362..71d830d7b923 100644
--- a/tools/perf/bench/sched-messaging.c
+++ b/tools/perf/bench/sched-messaging.c
@@ -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 {
diff --git a/tools/perf/builtin-inject.c b/tools/perf/builtin-inject.c
index 7e124a7b8bfd..8f983877c42d 100644
--- a/tools/perf/builtin-inject.c
+++ b/tools/perf/builtin-inject.c
@@ -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)
diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
index 1f57a7ecdf3d..02d64a9c6f64 100644
--- a/tools/perf/builtin-script.c
+++ b/tools/perf/builtin-script.c
@@ -2619,7 +2619,7 @@ 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);
diff --git a/tools/perf/builtin-timechart.c b/tools/perf/builtin-timechart.c
index 9e84fae9b096..0ba568efa939 100644
--- a/tools/perf/builtin-timechart.c
+++ b/tools/perf/builtin-timechart.c
@@ -128,7 +128,7 @@ struct sample_wrapper {
 	struct sample_wrapper *next;
 
 	u64		timestamp;
-	unsigned char	data[0];
+	unsigned char	data[];
 };
 
 #define TYPE_NONE	0
diff --git a/tools/perf/util/annotate.h b/tools/perf/util/annotate.h
index 2d88069d6428..0a0cd4f32175 100644
--- a/tools/perf/util/annotate.h
+++ b/tools/perf/util/annotate.h
@@ -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 {
diff --git a/tools/perf/util/branch.h b/tools/perf/util/branch.h
index 154a05cd03af..748f1d23a5c4 100644
--- a/tools/perf/util/branch.h
+++ b/tools/perf/util/branch.h
@@ -41,7 +41,7 @@ struct branch_entry {
 struct branch_stack {
 	u64			nr;
 	u64			hw_idx;
-	struct branch_entry	entries[0];
+	struct branch_entry	entries[];
 };
 
 /*
diff --git a/tools/perf/util/cputopo.h b/tools/perf/util/cputopo.h
index 7bf6b811f715..6201c3790d86 100644
--- a/tools/perf/util/cputopo.h
+++ b/tools/perf/util/cputopo.h
@@ -22,7 +22,7 @@ struct numa_topology_node {
 
 struct numa_topology {
 	u32				nr;
-	struct numa_topology_node	nodes[0];
+	struct numa_topology_node	nodes[];
 };
 
 struct cpu_topology *cpu_topology__new(void);
diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
index 2db64b79617a..d7ba29ad19ff 100644
--- a/tools/perf/util/dso.h
+++ b/tools/perf/util/dso.h
@@ -136,7 +136,7 @@ struct dso_cache {
 	struct rb_node	rb_node;
 	u64 offset;
 	u64 size;
-	char data[0];
+	char data[];
 };
 
 struct auxtrace_cache;
@@ -208,7 +208,7 @@ struct dso {
 	struct nsinfo	*nsinfo;
 	struct dso_id	 id;
 	refcount_t	 refcnt;
-	char		 name[0];
+	char		 name[];
 };
 
 /* dso__for_each_symbol - iterate over the symbols of given type
diff --git a/tools/perf/util/event.h b/tools/perf/util/event.h
index b8289f160f07..6ae01c3c2ffa 100644
--- a/tools/perf/util/event.h
+++ b/tools/perf/util/event.h
@@ -79,7 +79,7 @@ struct sample_read {
 
 struct ip_callchain {
 	u64 nr;
-	u64 ips[0];
+	u64 ips[];
 };
 
 struct branch_stack;
diff --git a/tools/perf/util/jitdump.c b/tools/perf/util/jitdump.c
index e3ccb0ce1938..32bb05e03fb2 100644
--- a/tools/perf/util/jitdump.c
+++ b/tools/perf/util/jitdump.c
@@ -57,7 +57,7 @@ struct debug_line_info {
 	unsigned long vma;
 	unsigned int lineno;
 	/* The filename format is unspecified, absolute path, relative etc. */
-	char const filename[0];
+	char const filename[];
 };
 
 struct jit_tool {
diff --git a/tools/perf/util/jitdump.h b/tools/perf/util/jitdump.h
index f2c3823cc81a..ab2842def83d 100644
--- a/tools/perf/util/jitdump.h
+++ b/tools/perf/util/jitdump.h
@@ -93,7 +93,7 @@ struct debug_entry {
 	uint64_t addr;
 	int lineno;	    /* source line number starting at 1 */
 	int discrim;	    /* column discriminator, 0 is default */
-	const char name[0]; /* null terminated filename, \xff\0 if same as previous entry */
+	const char name[]; /* null terminated filename, \xff\0 if same as previous entry */
 };
 
 struct jr_code_debug_info {
@@ -101,7 +101,7 @@ struct jr_code_debug_info {
 
 	uint64_t code_addr;
 	uint64_t nr_entry;
-	struct debug_entry entries[0];
+	struct debug_entry entries[];
 };
 
 struct jr_code_unwinding_info {
@@ -110,7 +110,7 @@ struct jr_code_unwinding_info {
 	uint64_t unwinding_size;
 	uint64_t eh_frame_hdr_size;
 	uint64_t mapped_size;
-	const char unwinding_data[0];
+	const char unwinding_data[];
 };
 
 union jr_entry {
diff --git a/tools/perf/util/ordered-events.h b/tools/perf/util/ordered-events.h
index 0920fb0ec6cc..75345946c4b9 100644
--- a/tools/perf/util/ordered-events.h
+++ b/tools/perf/util/ordered-events.h
@@ -29,7 +29,7 @@ typedef int (*ordered_events__deliver_t)(struct ordered_events *oe,
 
 struct ordered_events_buffer {
 	struct list_head	list;
-	struct ordered_event	event[0];
+	struct ordered_event	event[];
 };
 
 struct ordered_events {
diff --git a/tools/perf/util/pstack.c b/tools/perf/util/pstack.c
index 80ff41fc45be..a1d1e4ef6257 100644
--- a/tools/perf/util/pstack.c
+++ b/tools/perf/util/pstack.c
@@ -15,7 +15,7 @@
 struct pstack {
 	unsigned short	top;
 	unsigned short	max_nr_entries;
-	void		*entries[0];
+	void		*entries[];
 };
 
 struct pstack *pstack__new(unsigned short max_nr_entries)
diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
index 93fc43db1be3..ff4f4c47e148 100644
--- a/tools/perf/util/symbol.h
+++ b/tools/perf/util/symbol.h
@@ -55,7 +55,7 @@ struct symbol {
 	u8		inlined:1;
 	u8		arch_sym;
 	bool		annotate2;
-	char		name[0];
+	char		name[];
 };
 
 void symbol__delete(struct symbol *sym);
diff --git a/tools/perf/util/unwind-libunwind-local.c b/tools/perf/util/unwind-libunwind-local.c
index b4649f5a0c2f..9aededc0bc06 100644
--- a/tools/perf/util/unwind-libunwind-local.c
+++ b/tools/perf/util/unwind-libunwind-local.c
@@ -243,7 +243,7 @@ struct eh_frame_hdr {
 	 *    encoded_t fde_addr;
 	 * } binary_search_table[fde_count];
 	 */
-	char data[0];
+	char data[];
 } __packed;
 
 static int unwind_spec_ehframe(struct dso *dso, struct machine *machine,

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