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Subject[PATCH] char: mspec: Replace zero-length array with flexible-array member
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]

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 <gustavo@embeddedor.com>
---
drivers/char/mspec.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/char/mspec.c b/drivers/char/mspec.c
index a9d9f074fbd6..7d583222e8fa 100644
--- a/drivers/char/mspec.c
+++ b/drivers/char/mspec.c
@@ -75,7 +75,7 @@ struct vma_data {
enum mspec_page_type type; /* Type of pages allocated. */
unsigned long vm_start; /* Original (unsplit) base. */
unsigned long vm_end; /* Original (unsplit) end. */
- unsigned long maddr[0]; /* Array of MSPEC addresses. */
+ unsigned long maddr[]; /* Array of MSPEC addresses. */
};

/*
--
2.25.0
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