[PATCH 3/4] x86: signal: unify the sigaltstack check with other arches

[Stas Sergeev <stsp@list.ru>]

Currently x86's get_sigframe() checks for "current->sas_ss_size"
to determine whether there is a need to switch to sigaltstack.
The common practice used by all other arches is to check for
sas_ss_flags(sp) == 0

This patch makes the code consistent with other arches and also
allows for the further sigaltstack improvements within this patch serie.

CC: Andy Lutomirski <luto@amacapital.net>
CC: linux-kernel@vger.kernel.org
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Ingo Molnar <mingo@redhat.com>
CC: "H. Peter Anvin" <hpa@zytor.com>
CC: x86@kernel.org
CC: Borislav Petkov <bp@suse.de>
CC: Brian Gerst <brgerst@gmail.com>
CC: Oleg Nesterov <oleg@redhat.com>
CC: Richard Weinberger <richard@nod.at>

Signed-off-by: Stas Sergeev <stsp@users.sourceforge.net>
---
  arch/x86/kernel/signal.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index cb6282c..3955259 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -216,7 +216,7 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs 
*regs, size_t frame_size,
      if (!onsigstack) {
          /* This is the X/Open sanctioned signal stack switching. */
          if (ka->sa.sa_flags & SA_ONSTACK) {
-            if (current->sas_ss_size)
+            if (sas_ss_flags(sp) == 0)
                  sp = current->sas_ss_sp + current->sas_ss_size;
          } else if (config_enabled(CONFIG_X86_32) &&
                 (regs->ss & 0xffff) != __USER_DS &&
-- 
2.5.0