Minor - always set %esp immediately after setting %ss.
Setting %ss/%esp in sequence is guaranteed to be atomic. So, always
set them in this order to ensure irqs and nmis see a consistent
stack.
diff --git a/src/romlayout.S b/src/romlayout.S
index 4676d2f..c31d9cc 100644
--- a/src/romlayout.S
+++ b/src/romlayout.S
@@ -158,8 +158,8 @@
movw %ax, %ds
movw BDA_ebda_seg, %ax
// XXX - should verify ebda_seg looks sane.
- movw %ax, %ss
movw %ax, %ds
+ movw %ax, %ss
movl $EBDA_OFFSET_TOP_STACK, %esp
// Call handler.
diff --git a/src/util.c b/src/util.c
index af5dbd3..9d85b29 100644
--- a/src/util.c
+++ b/src/util.c
@@ -75,25 +75,24 @@
if (!MODE16)
__force_link_error__stack_hop_only_in_16bit_mode();
- u32 ebda_seg = get_ebda_seg();
- u32 tmp;
+ u16 ebda_seg = get_ebda_seg(), bkup_ss;
+ u32 bkup_esp;
asm volatile(
- // Backup current %ss value.
- "movl %%ss, %4\n"
- // Copy ebda seg to %ss and %ds
- "movl %3, %%ss\n"
- "movl %3, %%ds\n"
- // Backup %esp and set it to new value
- "movl %%esp, %3\n"
+ // Backup current %ss/%esp values.
+ "movw %%ss, %w3\n"
+ "movl %%esp, %4\n"
+ // Copy ebda seg to %ds/%ss and set %esp
+ "movw %w6, %%ds\n"
+ "movw %w6, %%ss\n"
"movl %5, %%esp\n"
// Call func
- "calll %6\n"
+ "calll %7\n"
// Restore segments and stack
- "movl %3, %%esp\n"
- "movl %4, %%ss\n"
- "movl %4, %%ds\n"
- : "+a" (eax), "+d" (edx), "+c" (ecx), "+r" (ebda_seg), "=r" (tmp)
- : "i" (EBDA_OFFSET_TOP_STACK), "m" (*(u8*)func)
+ "movw %w3, %%ds\n"
+ "movw %w3, %%ss\n"
+ "movl %4, %%esp\n"
+ : "+a" (eax), "+d" (edx), "+c" (ecx), "=&r" (bkup_ss), "=&r" (bkup_esp)
+ : "i" (EBDA_OFFSET_TOP_STACK), "r" (ebda_seg), "m" (*(u8*)func)
: "cc", "memory");
return eax;
}