[PATCH] i386: Fix places where using %gs changes the usermode ABI

There are a few places where the change in struct pt_regs and the use of %gs
affect the userspace ABI.  These are primarily debugging interfaces where
thread state can be inspected or extracted.
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Cc: Chuck Ebbert <76306.1226@compuserve.com>
Cc: Zachary Amsden <zach@vmware.com>
Cc: Jan Beulich <jbeulich@novell.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>

arch/i386/kernel/process.c

@@ -315,8 +315,8 @@ void show_regs(struct pt_regs * regs)
 		regs->eax,regs->ebx,regs->ecx,regs->edx);
 	printk("ESI: %08lx EDI: %08lx EBP: %08lx",
 		regs->esi, regs->edi, regs->ebp);
-	printk(" DS: %04x ES: %04x\n",
-		0xffff & regs->xds,0xffff & regs->xes);
+	printk(" DS: %04x ES: %04x GS: %04x\n",
+	       0xffff & regs->xds,0xffff & regs->xes, 0xffff & regs->xgs);
 
 	cr0 = read_cr0();
 	cr2 = read_cr2();
@@ -509,7 +509,7 @@ void dump_thread(struct pt_regs * regs, struct user * dump)
 	dump->regs.ds = regs->xds;
 	dump->regs.es = regs->xes;
 	savesegment(fs,dump->regs.fs);
-	savesegment(gs,dump->regs.gs);
+	dump->regs.gs = regs->xgs;
 	dump->regs.orig_eax = regs->orig_eax;
 	dump->regs.eip = regs->eip;
 	dump->regs.cs = regs->xcs;

arch/i386/kernel/ptrace.c

@@ -94,13 +94,9 @@ static int putreg(struct task_struct *child,
 				return -EIO;
 			child->thread.fs = value;
 			return 0;
-		case GS:
-			if (value && (value & 3) != 3)
-				return -EIO;
-			child->thread.gs = value;
-			return 0;
 		case DS:
 		case ES:
+		case GS:
 			if (value && (value & 3) != 3)
 				return -EIO;
 			value &= 0xffff;
@@ -116,8 +112,8 @@ static int putreg(struct task_struct *child,
 			value |= get_stack_long(child, EFL_OFFSET) & ~FLAG_MASK;
 			break;
 	}
-	if (regno > GS*4)
-		regno -= 2*4;
+	if (regno > ES*4)
+		regno -= 1*4;
 	put_stack_long(child, regno - sizeof(struct pt_regs), value);
 	return 0;
 }
@@ -131,18 +127,16 @@ static unsigned long getreg(struct task_struct *child,
 		case FS:
 			retval = child->thread.fs;
 			break;
-		case GS:
-			retval = child->thread.gs;
-			break;
 		case DS:
 		case ES:
+		case GS:
 		case SS:
 		case CS:
 			retval = 0xffff;
 			/* fall through */
 		default:
-			if (regno > GS*4)
-				regno -= 2*4;
+			if (regno > ES*4)
+				regno -= 1*4;
 			regno = regno - sizeof(struct pt_regs);
 			retval &= get_stack_long(child, regno);
 	}

include/asm-i386/elf.h

@@ -91,7 +91,7 @@ typedef struct user_fxsr_struct elf_fpxregset_t;
 	pr_reg[7] = regs->xds;				\
 	pr_reg[8] = regs->xes;				\
 	savesegment(fs,pr_reg[9]);			\
-	savesegment(gs,pr_reg[10]);			\
+	pr_reg[10] = regs->xgs;				\
 	pr_reg[11] = regs->orig_eax;			\
 	pr_reg[12] = regs->eip;				\
 	pr_reg[13] = regs->xcs;				\

include/asm-i386/unwind.h

@@ -71,6 +71,7 @@ static inline void arch_unw_init_blocked(struct unwind_frame_info *info)
 	info->regs.xss = __KERNEL_DS;
 	info->regs.xds = __USER_DS;
 	info->regs.xes = __USER_DS;
+	info->regs.xgs = __KERNEL_PDA;
 }
 
 extern asmlinkage int arch_unwind_init_running(struct unwind_frame_info *,