From: "Gustavo A. R. Silva" <gustavoars@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@alien8.de>,
"x86@kernel.org H. Peter Anvin" <hpa@zytor.com>
Cc: linux-kernel@vger.kernel.org,
"Gustavo A. R. Silva" <gustavo@embeddedor.com>
Subject: [PATCH] perf/x86: Replace zero-length array with flexible-array
Date: Mon, 11 May 2020 15:09:11 -0500 [thread overview]
Message-ID: <20200511200911.GA13149@embeddedor> (raw)
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>
---
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 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 */
--
2.26.2
next reply other threads:[~2020-05-11 20:04 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-11 20:09 Gustavo A. R. Silva [this message]
2020-05-19 18:44 ` [tip: perf/core] perf/x86: Replace zero-length array with flexible-array tip-bot2 for Gustavo A. R. Silva
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