Consistently use 16-byte alignment for MIPS N32 and N64.

- Add a new <machine/abi.h> header to hold constants shared between C
  and assembly such as CALLFRAME_SZ.
- Add a new STACK_ALIGN constant to <machine/abi.h> and use it to
  replace hardcoded constants in the kernel and makecontext().  As a
  result of this, ensure the stack pointer on N32 and N64 is 16-byte
  aligned for N32 and N64 after exec(), after pthread_create(), and
  when sending signals rather than 8-byte aligned.

Reviewed by:	jmallett
Sponsored by:	DARPA / AFRL
Differential Revision:	https://reviews.freebsd.org/D13875

1 files changed, 2 insertions, 4 deletions

diff --git a/lib/libc/mips/gen/makecontext.c b/lib/libc/mips/gen/makecontext.c
index 1f79c50bcda4..d15f1c991b92 100644
--- a/lib/libc/mips/gen/makecontext.c
+++ b/lib/libc/mips/gen/makecontext.c
@@ -38,6 +38,7 @@ __RCSID("$NetBSD: makecontext.c,v 1.5 2009/12/14 01:07:42 matt Exp $");
 #endif
 
 #include <sys/param.h>
+#include <machine/abi.h>
 #include <machine/regnum.h>
 
 #include <stdarg.h>
@@ -75,13 +76,10 @@ __makecontext(ucontext_t *ucp, void (*func)(void), int argc, ...)
 	    ((uintptr_t)ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size);
 #if defined(__mips_o32) || defined(__mips_o64)
 	sp -= (argc >= 4 ? argc : 4);	/* Make room for >=4 arguments. */
-	sp  = (register_t *)
-	    ((uintptr_t)sp & ~0x7);	/* Align on double-word boundary. */
 #elif defined(__mips_n32) || defined(__mips_n64)
 	sp -= (argc > 8 ? argc - 8 : 0); /* Make room for > 8 arguments. */
-	sp  = (register_t *)
-	    ((uintptr_t)sp & ~0xf);	/* Align on quad-word boundary. */
 #endif
+	sp  = (register_t *)((uintptr_t)sp & ~(STACK_ALIGN - 1));
 
 	mc->mc_regs[SP] = (intptr_t)sp;
 	mc->mc_regs[S0] = (intptr_t)ucp;