* [PATCH] perf/core: Replace zero-length array with flexible-array
@ 2020-05-11 20:12 Gustavo A. R. Silva
2020-05-19 18:44 ` [tip: perf/core] " tip-bot2 for Gustavo A. R. Silva
0 siblings, 1 reply; 2+ messages in thread
From: Gustavo A. R. Silva @ 2020-05-11 20:12 UTC (permalink / raw)
To: Peter Zijlstra, Ingo Molnar, Arnaldo Carvalho de Melo,
Mark Rutland, Alexander Shishkin, Jiri Olsa, Namhyung Kim
Cc: linux-kernel, Gustavo A. R. Silva
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@kernel.org>
---
include/linux/perf_event.h | 4 ++--
kernel/events/callchain.c | 2 +-
kernel/events/internal.h | 2 +-
3 files changed, 4 insertions(+), 4 deletions(-)
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);
--
2.26.2
^ permalink raw reply related [flat|nested] 2+ messages in thread
* [tip: perf/core] perf/core: Replace zero-length array with flexible-array
2020-05-11 20:12 [PATCH] perf/core: Replace zero-length array with flexible-array Gustavo A. R. Silva
@ 2020-05-19 18:44 ` tip-bot2 for Gustavo A. R. Silva
0 siblings, 0 replies; 2+ messages in thread
From: tip-bot2 for Gustavo A. R. Silva @ 2020-05-19 18:44 UTC (permalink / raw)
To: linux-tip-commits; +Cc: Gustavo A. R. Silva, Peter Zijlstra (Intel), x86, LKML
The following commit has been merged into the perf/core branch of tip:
Commit-ID: c50c75e9b87946499a62bffc021e95c87a1d57cd
Gitweb: https://git.kernel.org/tip/c50c75e9b87946499a62bffc021e95c87a1d57cd
Author: Gustavo A. R. Silva <gustavoars@kernel.org>
AuthorDate: Mon, 11 May 2020 15:12:27 -05:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Tue, 19 May 2020 20:34:16 +02:00
perf/core: 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@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200511201227.GA14041@embeddedor
---
include/linux/perf_event.h | 4 ++--
kernel/events/callchain.c | 2 +-
kernel/events/internal.h | 2 +-
3 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 87e2168..d7b610c 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 c2b41a2..b199104 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 f16f66b..fcbf561 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);
^ permalink raw reply related [flat|nested] 2+ messages in thread
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2020-05-11 20:12 [PATCH] perf/core: Replace zero-length array with flexible-array Gustavo A. R. Silva
2020-05-19 18:44 ` [tip: perf/core] " tip-bot2 for Gustavo A. R. Silva
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