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Date: Mon, 11 May 2020 12:48:12 -0300
From: Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
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: Re: [PATCH] perf script: Replace zero-length array with
flexible-array
Em Thu, May 07, 2020 at 02:06:15PM -0500, Gustavo A. R. Silva escreveu:
> 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[];
> };
Can you split this into a kernel part and tools/ one? Also this is not
really just for "perf script", so please adjust the subject line too :-)
- Arnaldo
> 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,
>
--
- Arnaldo
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