Remove useless segments push/pop in VMXAssist.

According to Intel Spec, segments registors are cleared when exiting
virtual-8086 mode through trap or interrupts gate, so it's no need to
save their values in stack.
Signed-off-by: Xin Li <xin.b.li@intel.com>

tools/firmware/vmxassist/setup.c

@@ -66,7 +66,7 @@ struct vmx_assist_context newctx;
 unsigned long memory_size;
 int initialize_real_mode;
 
-extern char stack[], stack_top[];
+extern char stack_top[];
 extern unsigned trap_handlers[];
 
 void
@@ -201,7 +201,7 @@ void
 enter_real_mode(struct regs *regs)
 {
 	/* mask off TSS busy bit */
-        gdt[TSS_SELECTOR / sizeof(gdt[0])] &= ~0x0000020000000000ULL;
+	gdt[TSS_SELECTOR / sizeof(gdt[0])] &= ~0x0000020000000000ULL;
 
 	/* start 8086 emulation of BIOS */
 	if (initialize_real_mode) {
@@ -219,8 +219,10 @@ enter_real_mode(struct regs *regs)
 			regs->cs = booting_vector << 8; /* AP entry point */
 			regs->eip = 0;
 		}
-		regs->uesp = 0;
-		regs->uss = 0;
+
+		regs->uesp = regs->uss = 0;
+		regs->eax = regs->ecx = regs->edx = regs->ebx = 0;
+		regs->esp = regs->ebp = regs->esi = regs->edi = 0;
 
 		/* intercept accesses to the PIC */
 		setiomap(PIC_MASTER+PIC_CMD);
@@ -236,14 +238,12 @@ enter_real_mode(struct regs *regs)
 
 		/* this should get us into 16-bit mode */
 		return;
-	} else {
-		/* go from protected to real mode */
-		regs->eflags |= EFLAGS_VM;
-
-		set_mode(regs, VM86_PROTECTED_TO_REAL);
-
-		emulate(regs);
 	}
+
+	/* go from protected to real mode */
+	regs->eflags |= EFLAGS_VM;
+	set_mode(regs, VM86_PROTECTED_TO_REAL);
+	emulate(regs);
 }
 
 /*

tools/firmware/vmxassist/trap.S

@@ -100,10 +100,6 @@ trap_handlers:
 	.code32
 	.align	16
 common_trap:				/* common trap handler */
-	pushl	%gs
-	pushl	%fs
-	pushl	%ds
-	pushl	%es
 	pushal
 
 	movl	$(DATA_SELECTOR), %eax	/* make sure these are sane */
@@ -114,17 +110,13 @@ common_trap:				/* common trap handler */
 	movl	%esp, %ebp
 
 	pushl	%ebp
-	pushl	52(%ebp)
-	pushl	48(%ebp)
+	pushl	36(%ebp)
+	pushl	32(%ebp)
 	call	trap			/* trap(trapno, errno, regs) */
 	addl	$12, %esp
 
 trap_return:
 	popal
-	popl	%es
-	popl	%ds
-	popl	%fs
-	popl	%gs
 	addl	$8, %esp		/* skip trapno, errno */
 	iret
 	/* NOT REACHED */
@@ -152,10 +144,6 @@ switch_to_real_mode:
 	pushl	oldctx+VMX_ASSIST_CTX_EIP
 	pushl	$-1			/* trapno, errno */
 	pushl	$-1
-	pushl	%gs
-	pushl	%fs
-	pushl	%ds
-	pushl	%es
 	pushal
 
 	movl	%esp, %ebp

tools/firmware/vmxassist/util.c

@@ -62,17 +62,15 @@ dump_regs(struct regs *regs)
 		regs->eax, regs->ecx, regs->edx, regs->ebx);
 	printf("esp    %8x ebp    %8x esi    %8x edi    %8x\n",
 		regs->esp, regs->ebp, regs->esi, regs->edi);
-	printf("es     %8x ds     %8x fs     %8x gs     %8x\n",
-		regs->es, regs->ds, regs->fs, regs->gs);
 	printf("trapno %8x errno  %8x\n", regs->trapno, regs->errno);
 	printf("eip    %8x cs     %8x eflags %8x\n",
 		regs->eip, regs->cs, regs->eflags);
-	printf("uesp   %8x uss    %8x \n",
+	printf("uesp   %8x uss    %8x\n",
 		regs->uesp, regs->uss);
 	printf("ves    %8x vds    %8x vfs    %8x vgs    %8x\n",
 		regs->ves, regs->vds, regs->vfs, regs->vgs);
 
-	printf("cr0    %8lx cr2    %8x cr3    %8lx cr4    %8lx\n",
+	printf("cr0    %8lx cr2    %8x cr3    %8lx cr4    %8lx\n\n",
 		(long)oldctx.cr0, get_cr2(),
 		(long)oldctx.cr3, (long)oldctx.cr4);
 }

tools/firmware/vmxassist/vm86.c

@@ -376,9 +376,9 @@ segment(unsigned prefix, struct regs *regs, unsigned seg)
 	if (prefix & SEG_SS)
 		seg = regs->uss;
 	if (prefix & SEG_FS)
-		seg = regs->fs;
+		seg = regs->vfs;
 	if (prefix & SEG_GS)
-		seg = regs->gs;
+		seg = regs->vgs;
 	return seg;
 }
 
@@ -934,6 +934,8 @@ load_or_clear_seg(unsigned long sel, uint32_t *base, uint32_t *limit, union vmcs
 static void
 protected_mode(struct regs *regs)
 {
+	extern char stack_top[];
+
 	regs->eflags &= ~(EFLAGS_TF|EFLAGS_VM);
 
 	oldctx.eip = regs->eip;
@@ -958,12 +960,10 @@ protected_mode(struct regs *regs)
 			  &oldctx.gs_limit, &oldctx.gs_arbytes);
 
 	/* initialize jump environment to warp back to protected mode */
+	regs->uss = DATA_SELECTOR;
+	regs->uesp = stack_top;
 	regs->cs = CODE_SELECTOR;
-	regs->ds = DATA_SELECTOR;
-	regs->es = DATA_SELECTOR;
-	regs->fs = DATA_SELECTOR;
-	regs->gs = DATA_SELECTOR;
-	regs->eip = (unsigned) &switch_to_protected_mode;
+	regs->eip = (unsigned) switch_to_protected_mode;
 
 	/* this should get us into 32-bit mode */
 }
@@ -975,10 +975,6 @@ static void
 real_mode(struct regs *regs)
 {
 	regs->eflags |= EFLAGS_VM | 0x02;
-	regs->ds = DATA_SELECTOR;
-	regs->es = DATA_SELECTOR;
-	regs->fs = DATA_SELECTOR;
-	regs->gs = DATA_SELECTOR;
 
 	/*
 	 * When we transition from protected to real-mode and we
@@ -1070,9 +1066,6 @@ set_mode(struct regs *regs, enum vm86_mode newmode)
 	case VM86_PROTECTED:
 		if (mode == VM86_REAL_TO_PROTECTED) {
 			protected_mode(regs);
-//			printf("<VM86_PROTECTED>\n");
-			mode = newmode;
-			return;
 		} else
 			panic("unexpected protected mode transition");
 		break;

tools/firmware/vmxassist/vm86.h

@@ -34,7 +34,6 @@
 
 struct regs {
 	unsigned	edi, esi, ebp, esp, ebx, edx, ecx, eax;
-	unsigned	es, ds, fs, gs;
 	unsigned	trapno, errno;
 	unsigned	eip, cs, eflags, uesp, uss;
 	unsigned	ves, vds, vfs, vgs;
@@ -55,7 +54,6 @@ enum vm86_mode {
 
 extern enum vm86_mode prevmode, mode;
 extern struct vmx_assist_context oldctx;
-extern struct vmx_assist_context newctx;
 
 extern void emulate(struct regs *);
 extern void dump_regs(struct regs *);