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R. Silva" Cc: Peter Zijlstra , Ingo Molnar , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , linux-kernel@vger.kernel.org Subject: Re: [PATCH] perf script: Replace zero-length array with flexible-array Message-ID: <20200511154812.GD5377@kernel.org> References: <20200507190615.GA15677@embeddedor> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200507190615.GA15677@embeddedor> X-Url: http://acmel.wordpress.com Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > --- > 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