Recently the kernel test robot has reported an ARM-specific BUILD_BUG_ON()
in an old and unmaintained wil6210 wireless driver. The problem comes from
the structure packing rules of old ARM ABI ('-mabi=apcs-gnu'). For example,
the following structure is packed to 18 bytes instead of 16:
struct poorly_packed {
unsigned int a;
unsigned int b;
unsigned short c;
union {
struct {
unsigned short d;
unsigned int e;
} __attribute__((packed));
struct {
unsigned short d;
unsigned int e;
} __attribute__((packed)) inner;
};
} __attribute__((packed));
To fit it into 16 bytes, it's required to add packed attribute to the
container union as well:
struct poorly_packed {
unsigned int a;
unsigned int b;
unsigned short c;
union {
struct {
unsigned short d;
unsigned int e;
} __attribute__((packed));
struct {
unsigned short d;
unsigned int e;
} __attribute__((packed)) inner;
} __attribute__((packed));
} __attribute__((packed));
Thanks to Andrew Pinski of GCC team for sorting the things out at
https://gcc.gnu.org/pipermail/gcc/2023-November/242888.html.
Reported-by: kernel test robot <[email protected]>
Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]
Signed-off-by: Dmitry Antipov <[email protected]>
---
include/uapi/linux/stddef.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/uapi/linux/stddef.h b/include/uapi/linux/stddef.h
index 5c6c4269f7ef..2ec6f35cda32 100644
--- a/include/uapi/linux/stddef.h
+++ b/include/uapi/linux/stddef.h
@@ -27,7 +27,7 @@
union { \
struct { MEMBERS } ATTRS; \
struct TAG { MEMBERS } ATTRS NAME; \
- }
+ } ATTRS
#ifdef __cplusplus
/* sizeof(struct{}) is 1 in C++, not 0, can't use C version of the macro. */
--
2.42.0