On 29. 05. 24, 23:29, Nathan Chancellor wrote:
Work for __counted_by on generic pointers in structures (not just
flexible array members) has started landing in Clang 19 (current tip of
tree). During the development of this feature, a restriction was added
to __counted_by to prevent the flexible array member's element type from
including a flexible array member itself such as:
struct foo {
int count;
char buf[];
};
struct bar {
int count;
struct foo data[] __counted_by(count);
};
because the size of data cannot be calculated with the standard array
size formula:
sizeof(struct foo) * count
This restriction was downgraded to a warning but due to CONFIG_WERROR,
it can still break the build. The application of __counted_by on the
ports member of 'struct mxser_board' triggers this restriction,
resulting in:
drivers/tty/mxser.c:291:2: error: 'counted_by' should not be applied to an array with element of unknown size because 'struct mxser_port' is a struct type with a flexible array member.
Huh -- what am I missing:
struct mxser_port {
struct tty_port port;
struct mxser_board *board;
unsigned long ioaddr;
unsigned long opmode_ioaddr;
u8 rx_high_water;
u8 rx_low_water;
int type; /* UART type */
u8 x_char; /* xon/xoff character */
u8 IER; /* Interrupt Enable Register */
u8 MCR; /* Modem control register */
u8 FCR; /* FIFO control register */
struct async_icount icount;
unsigned int timeout;
u8 read_status_mask;
u8 ignore_status_mask;
u8 xmit_fifo_size;
spinlock_t slock;
};
?
This will be an error in a future compiler version [-Werror,-Wbounds-safety-counted-by-elt-type-unknown-size]
291 | struct mxser_port ports[] __counted_by(nports);
| ^~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.
Remove this use of __counted_by to fix the warning/error. However,
rather than remove it altogether, leave it commented, as it may be
possible to support this in future compiler releases.
This looks like a compiler bug/deficiency.
What does gcc say BTW?
Cc: stable@xxxxxxxxxxxxxxx
Closes: https://github.com/ClangBuiltLinux/linux/issues/2026
Fixes: f34907ecca71 ("mxser: Annotate struct mxser_board with __counted_by")
I would not say "Fixes" here. It only works around a broken compiler.
Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx>
---
drivers/tty/mxser.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/tty/mxser.c b/drivers/tty/mxser.c
index 458bb1280ebf..5b97e420a95f 100644
--- a/drivers/tty/mxser.c
+++ b/drivers/tty/mxser.c
@@ -288,7 +288,7 @@ struct mxser_board {
enum mxser_must_hwid must_hwid;
speed_t max_baud;
- struct mxser_port ports[] __counted_by(nports);
+ struct mxser_port ports[] /* __counted_by(nports) */;
};
static DECLARE_BITMAP(mxser_boards, MXSER_BOARDS);
thanks,
--
js
suse labs
