The patch titled
Subject: fs/select: avoid clang stack usage warning
has been added to the -mm tree. Its filename is
fs-select-avoid-clang-stack-usage-warning.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/fs-select-avoid-clang-stack-usage-warning.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/fs-select-avoid-clang-stack-usage-warning.patch
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The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Arnd Bergmann <arnd@xxxxxxxx>
Subject: fs/select: avoid clang stack usage warning
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.
Link: http://lkml.kernel.org/r/20190307090146.1874906-1-arnd@xxxxxxxx
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
Reviewed-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: "Darrick J. Wong" <darrick.wong@xxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/poll.h | 4 ++++
1 file changed, 4 insertions(+)
--- a/include/linux/poll.h~fs-select-avoid-clang-stack-usage-warning
+++ a/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
_
Patches currently in -mm which might be from arnd@xxxxxxxx are
fs-select-avoid-clang-stack-usage-warning.patch
