[PATCH] perf tools: Replace zero-length array with flexible-array

From: Gustavo A. R. Silva
Date: Mon May 11 2020 - 15:52:14 EST

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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 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
---
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 +-
15 files changed, 19 insertions(+), 19 deletions(-)

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,
--
2.26.2

Next message: Nick Desaulniers: "Re: [PATCH] x86: support i386 with Clang"
Previous message: Alan Stern: "Re: [PATCH v9 4/5] usb: ehci: Add new EHCI driver for Broadcom STB SoC's"
Next in thread: Arnaldo Melo: "Re: [PATCH] perf tools: Replace zero-length array with flexible-array"
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