real mode support (now boots from BOCHS BIOS and LGPL'ed VGA BIOS)

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@333 c046a42c-6fe2-441c-8c8c-71466251a162

1 files changed, 31 insertions, 0 deletions

diff --git a/helper-i386.c b/helper-i386.c
index 72b75a5c21..3f63704d5a 100644
--- a/helper-i386.c
+++ b/helper-i386.c
@@ -788,6 +788,37 @@ static inline void load_seg_vm(int seg, int selector)
     sc->limit = 0xffff;
 }
 
+/* real mode iret */
+void helper_iret_real(int shift)
+{
+    uint32_t sp, new_cs, new_eip, new_eflags, new_esp;
+    uint8_t *ssp;
+    int eflags_mask;
+    
+    sp = env->regs[R_ESP] & 0xffff;
+    ssp = env->segs[R_SS].base + sp;
+    if (shift == 1) {
+        /* 32 bits */
+        new_eflags = ldl(ssp + 8);
+        new_cs = ldl(ssp + 4) & 0xffff;
+        new_eip = ldl(ssp) & 0xffff;
+    } else {
+        /* 16 bits */
+        new_eflags = lduw(ssp + 4);
+        new_cs = lduw(ssp + 2);
+        new_eip = lduw(ssp);
+    }
+    new_esp = sp + (6 << shift);
+    env->regs[R_ESP] = (env->regs[R_ESP] & 0xffff0000) | 
+        (new_esp & 0xffff);
+    load_seg_vm(R_CS, new_cs);
+    env->eip = new_eip;
+    eflags_mask = FL_UPDATE_CPL0_MASK;
+    if (shift == 0)
+        eflags_mask &= 0xffff;
+    load_eflags(new_eflags, eflags_mask);
+}
+
 /* protected mode iret */
 void helper_iret_protected(int shift)
 {