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Date: Mon, 11 May 2020 17:20:08 -0300
From: Arnaldo Melo <arnaldo.melo@...il.com>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...hat.com>,
Namhyung Kim <namhyung@...nel.org>
CC: linux-kernel@...r.kernel.org,
"Gustavo A. R. Silva" <gustavo@...eddedor.com>
Subject: Re: [PATCH] perf tools: Replace zero-length array with flexible-array
On May 11, 2020 4:56:43 PM GMT-03:00, "Gustavo A. R. Silva" <gustavoars@...nel.org> wrote:
>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.
Thanks, applied
- Arnaldo
>
>[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>
>---
> 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,
--
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