| Message ID | 20190307090146.1874906-1-arnd@arndb.de |
|---|---|
| State | Accepted |
| Commit | ad312f95d41c9de19313c51e388c4984451c010f |
| Headers | show |
| Series | fs/select: avoid clang stack usage warning | expand |
On Thu, Mar 07, 2019 at 10:01:36AM +0100, Arnd Bergmann wrote: > 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. Could just use 768 bytes unconditionally. I doubt a few bytes more or less will make too much difference. Other than that Reviewed-by: Andi Kleen <ak@linux.intel.com> -Andi
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
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(+) -- 2.20.0