Commit e6d9a525 authored May 11, 2016 by Colin Ian King Committed by Will Deacon May 12, 2016

arm64: do not enforce strict 16 byte alignment to stack pointer



copy_thread should not be enforcing 16 byte aligment and returning
-EINVAL. Other architectures trap misaligned stack access with SIGBUS
so arm64 should follow this convention, so remove the strict enforcement
check.

For example, currently clone(2) fails with -EINVAL when passing
a misaligned stack and this gives little clue to what is wrong. Instead,
it is arguable that a SIGBUS on the fist access to a misaligned stack
allows one to figure out that it is a misaligned stack issue rather
than trying to figure out why an unconventional (and undocumented)
-EINVAL is being returned.

Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

parent 61462c8a

arch/arm64/kernel/process.c

+0 −3

Original line number	Diff line number	Diff line
		@@ -265,9 +265,6 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start,
		if (stack_start) {
		if (is_compat_thread(task_thread_info(p)))
		childregs->compat_sp = stack_start;
		/* 16-byte aligned stack mandatory on AArch64 */
		else if (stack_start & 15)
		return -EINVAL;
		else
		childregs->sp = stack_start;
		}