Re: [PATCH] fs/select: avoid clang stack usage warning

From: Andi Kleen
Date: Thu Mar 07 2019 - 11:19:58 EST

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@xxxxxxxxxxxxxxx>