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6507 i386 makecontext(3c) needs to 16-byte align the stack
*** 25,36 ****
*/
/* Copyright (c) 1988 AT&T */
/* All Rights Reserved */
- #pragma ident "%Z%%M% %I% %E% SMI"
-
#pragma weak _makecontext = makecontext
#include "lint.h"
#include <stdarg.h>
#include <ucontext.h>
--- 25,34 ----
*** 44,53 ****
--- 42,77 ----
* When makecontext() returns, the ucontext_t will be set to run the
* given function with the given parameters on the stack specified by
* uc_stack, and which will return to the ucontext_t specified by uc_link.
*/
+ /*
+ * The original i386 ABI said that the stack pointer need be only 4-byte
+ * aligned before a function call (STACK_ALIGN == 4). The ABI supplement
+ * version 1.0 changed the required alignment to 16-byte for the benefit of
+ * floating point code compiled using sse2. The compiler assumes this
+ * alignment and maintains it for calls it generates. If the stack is
+ * initially properly aligned, it will continue to be so aligned. If it is
+ * not initially so aligned, it will never become so aligned.
+ *
+ * One slightly confusing detail to keep in mind is that the 16-byte
+ * alignment (%esp & 0xf == 0) is true just *before* the call instruction.
+ * The call instruction will then push a return value, decrementing %esp by
+ * 4. Therefore, if one dumps %esp at the at the very first instruction in
+ * a function, it will end with a 0xc. The compiler expects this and
+ * compensates for it properly.
+ *
+ * Note: If you change this value, you need to change it in the following
+ * files as well:
+ *
+ * - lib/libc/i386/threads/machdep.c
+ * - lib/common/i386/crti.s
+ * - lib/common/i386/crt1.s
+ */
+ #undef STACK_ALIGN
+ #define STACK_ALIGN 16
+
static void resumecontext(void);
void
makecontext(ucontext_t *ucp, void (*func)(), int argc, ...)
{
*** 58,83 ****
ucp->uc_mcontext.gregs[EIP] = (greg_t)func;
size = sizeof (long) * (argc + 1);
! sp = (long *)(((uintptr_t)ucp->uc_stack.ss_sp +
ucp->uc_stack.ss_size - size) & ~(STACK_ALIGN - 1));
! tsp = sp + 1;
!
! va_start(ap, argc);
!
! while (argc-- > 0) {
! *tsp++ = va_arg(ap, long);
! }
!
! va_end(ap);
*sp = (long)resumecontext; /* return address */
ucp->uc_mcontext.gregs[UESP] = (greg_t)sp;
}
static void
resumecontext(void)
--- 82,112 ----
ucp->uc_mcontext.gregs[EIP] = (greg_t)func;
size = sizeof (long) * (argc + 1);
! tsp = (long *)(((uintptr_t)ucp->uc_stack.ss_sp +
ucp->uc_stack.ss_size - size) & ~(STACK_ALIGN - 1));
! /*
! * Since we're emulating the call instruction, we must push the
! * return address (which involves adjusting the stack pointer to
! * have the proper 4-byte bias).
! */
! sp = tsp - 1;
*sp = (long)resumecontext; /* return address */
ucp->uc_mcontext.gregs[UESP] = (greg_t)sp;
+
+ /*
+ * "push" all the arguments
+ */
+ va_start(ap, argc);
+ while (argc-- > 0)
+ *tsp++ = va_arg(ap, long);
+ va_end(ap);
}
static void
resumecontext(void)