Messages in this thread Patch in this message | | | Date | Thu, 7 May 2020 13:54:13 -0500 | From | "Gustavo A. R. Silva" <> | Subject | [PATCH] treewide: Replace zero-length array with flexible-array |
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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> --- samples/mei/mei-amt-version.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/samples/mei/mei-amt-version.c b/samples/mei/mei-amt-version.c index 32234481ad7d..ad3e56042f96 100644 --- a/samples/mei/mei-amt-version.c +++ b/samples/mei/mei-amt-version.c @@ -267,7 +267,7 @@ struct amt_host_if_msg_header { struct amt_host_if_resp_header { struct amt_host_if_msg_header header; uint32_t status; - unsigned char data[0]; + unsigned char data[]; } __attribute__((packed)); const uuid_le MEI_IAMTHIF = UUID_LE(0x12f80028, 0xb4b7, 0x4b2d, \
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