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>
Cc: linux-kernel@vger.kernel.org,
"Gustavo A. R. Silva" <gustavo@embeddedor.com>
Subject: [PATCH perf/core] perf branch: Replace zero-length array with flexible-array
Date: Wed, 20 May 2020 14:16:13 -0500 [thread overview]
Message-ID: <20200520191613.GA26869@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 and audited _manually_.
[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>
---
tools/perf/util/branch.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/tools/perf/util/branch.h b/tools/perf/util/branch.h
index 4d3f02fa223df..17b2ccc61094b 100644
--- a/tools/perf/util/branch.h
+++ b/tools/perf/util/branch.h
@@ -46,7 +46,7 @@ struct branch_entry {
struct branch_stack {
u64 nr;
u64 hw_idx;
- struct branch_entry entries[0];
+ struct branch_entry entries[];
};
/*
--
2.26.2
reply other threads:[~2020-05-20 19:11 UTC|newest]
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