On Fri, Oct 7, 2022 at 6:46 PM Andi Kleen <ak@xxxxxxxxxxxxxxx> wrote: > > > On 10/6/2022 3:21 PM, Nick Desaulniers wrote: > > 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. > >> > >> 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 > > Hi Arnd, > > Upon a toolchain upgrade for Android, our 32b x86 image used for > > first-party developer VMs started tripping -Wframe-larger-than= again > > (thanks -Werror) which is blocking our ability to upgrade our toolchain. > > > I wonder if there is a way to disable the warning or increase the > threshold just for this function. I don't think attribute optimize would > work, but perhaps some pragma? Here's what I would have guessed, the pragma approach seems a little broken. https://godbolt.org/z/vY7fGYv7f Maybe I'm holding it wrong? > > > -Andi > > > -- Thanks, ~Nick Desaulniers
