[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>

4 files changed, 11 insertions, 16 deletions

diff --git a/arch/i386/kernel/process.c b/arch/i386/kernel/process.c
index 905364d42847..dc4272545179 100644
--- a/arch/i386/kernel/process.c
+++ b/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;
diff --git a/arch/i386/kernel/ptrace.c b/arch/i386/kernel/ptrace.c
index 775f50e9395b..f3f94ac5736a 100644
--- a/arch/i386/kernel/ptrace.c
+++ b/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);
         }
diff --git a/include/asm-i386/elf.h b/include/asm-i386/elf.h
index 3a05436f31c0..45d21a0c95bf 100644
--- a/include/asm-i386/elf.h
+++ b/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;                         \
diff --git a/include/asm-i386/unwind.h b/include/asm-i386/unwind.h
index 5031d693b89d..601fc67bd775 100644
--- a/include/asm-i386/unwind.h
+++ b/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 *,