The select() implementation is carefully tuned to put a sensible amount
of data on the stack for holding a copy of the user space fd_set,
but not too large to risk overflowing the kernel stack.
When building a 32-bit kernel with clang, we need a little more space
than with gcc, which often triggers a warning:
fs/select.c:619:5: error: stack frame size of 1048 bytes in function 'core_sys_select' [-Werror,-Wframe-larger-than=]
int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp,
I experimentally found that for 32-bit ARM, reducing the maximum
stack usage by 64 bytes keeps us reliably under the warning limit
again.
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
---
include/linux/poll.h | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/include/linux/poll.h b/include/linux/poll.h
index 7e0fdcf905d2..1cdc32b1f1b0 100644
--- a/include/linux/poll.h
+++ b/include/linux/poll.h
@@ -16,7 +16,11 @@
extern struct ctl_table epoll_table[]; /* for sysctl */
/* ~832 bytes of stack space used max in sys_select/sys_poll before allocating
additional memory. */
+#ifdef __clang__
+#define MAX_STACK_ALLOC 768
+#else
#define MAX_STACK_ALLOC 832
+#endif
#define FRONTEND_STACK_ALLOC 256
#define SELECT_STACK_ALLOC FRONTEND_STACK_ALLOC
#define POLL_STACK_ALLOC FRONTEND_STACK_ALLOC
--
2.20.0
