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@@ -47,13 +47,13 @@
/*
* 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 made from that function. 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.
+ * 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
@@ -85,23 +85,28 @@
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;
- 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;
+
+ /*
+ * "push" all the arguments
+ */
+ va_start(ap, argc);
+ while (argc-- > 0)
+ *tsp++ = va_arg(ap, long);
+ va_end(ap);
}
static void
resumecontext(void)