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* [PATCH] fs/select: avoid clang stack usage warning
@ 2019-03-07  9:01 Arnd Bergmann
  2019-03-07 16:19 ` Andi Kleen
  2022-10-06 22:21 ` Nick Desaulniers
  0 siblings, 2 replies; 21+ messages in thread
From: Arnd Bergmann @ 2019-03-07  9:01 UTC (permalink / raw)
  To: linux-fsdevel
  Cc: Nick Desaulniers, Alexander Viro, Andrew Morton, Andi Kleen,
	Christoph Hellwig, Eric Dumazet, Arnd Bergmann, Darrick J. Wong,
	Greg Kroah-Hartman, linux-kernel

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@arndb.de>
---
 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


^ permalink raw reply related	[flat|nested] 21+ messages in thread

end of thread, other threads:[~2022-10-14 22:39 UTC | newest]

Thread overview: 21+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-03-07  9:01 [PATCH] fs/select: avoid clang stack usage warning Arnd Bergmann
2019-03-07 16:19 ` Andi Kleen
2022-10-06 22:21 ` Nick Desaulniers
2022-10-07  8:28   ` Arnd Bergmann
2022-10-07 19:04     ` Nick Desaulniers
2022-10-07 20:11       ` [PATCH] fs/select: mark do_select noinline_for_stack for 32b Nick Desaulniers
2022-10-10  7:44         ` Christoph Hellwig
2022-10-10 16:42           ` Nick Desaulniers
2022-10-10 19:55         ` Arnd Bergmann
2022-10-13 18:52         ` kernel test robot
2022-10-07 21:42       ` [PATCH] fs/select: avoid clang stack usage warning Arnd Bergmann
2022-10-07 22:54         ` Nick Desaulniers
2022-10-10 18:40           ` Nick Desaulniers
2022-10-11 12:46             ` Arnd Bergmann
2022-10-11 20:55               ` [PATCH v2] fs/select: mark do_select noinline_for_stack Nick Desaulniers
2022-10-14 22:39                 ` Nathan Chancellor
2022-10-07 23:17         ` [PATCH] fs/select: avoid clang stack usage warning Kees Cook
2022-10-09 10:49       ` David Laight
2022-10-08  1:46   ` Andi Kleen
2022-10-11 20:50     ` Nick Desaulniers
2022-10-13 20:52       ` Andi Kleen

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