The following commit has been merged into the perf/core branch of tip:
Commit-ID: 8ac7571a8cd3c11da24c3c3555f6e40e33049609
Gitweb: https://git.kernel.org/tip/8ac7571a8cd3c11da24c3c3555f6e40e33049609
Author: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
AuthorDate: Mon, 11 May 2020 15:09:11 -05:00
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Tue, 19 May 2020 20:34:16 +02:00
perf/x86: 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@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20200511200911.GA13149@embeddedor
---
arch/x86/events/intel/bts.c | 2 +-
arch/x86/events/intel/uncore.h | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/events/intel/bts.c b/arch/x86/events/intel/bts.c
index 6a3b599..731dd8d 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 0da4a46..b469ddd 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 */
|