1 files changed, 28 insertions, 14 deletions

diff --git a/arch/sparc/kernel/signal_64.c b/arch/sparc/kernel/signal_64.c
index a2b81598d905..f0836cd0e2f2 100644
--- a/arch/sparc/kernel/signal_64.c
+++ b/arch/sparc/kernel/signal_64.c
@@ -529,11 +529,27 @@ static void do_signal(struct pt_regs *regs, unsigned long orig_i0)
         siginfo_t info;
         int signr;
         
+        /* It's a lot of work and synchronization to add a new ptrace
+         * register for GDB to save and restore in order to get
+         * orig_i0 correct for syscall restarts when debugging.
+         *
+         * Although it should be the case that most of the global
+         * registers are volatile across a system call, glibc already
+         * depends upon that fact that we preserve them.  So we can't
+         * just use any global register to save away the orig_i0 value.
+         *
+         * In particular %g2, %g3, %g4, and %g5 are all assumed to be
+         * preserved across a system call trap by various pieces of
+         * code in glibc.
+         *
+         * %g7 is used as the "thread register".   %g6 is not used in
+         * any fixed manner.  %g6 is used as a scratch register and
+         * a compiler temporary, but it's value is never used across
+         * a system call.  Therefore %g6 is usable for orig_i0 storage.
+         */
         if (pt_regs_is_syscall(regs) &&
-            (regs->tstate & (TSTATE_XCARRY | TSTATE_ICARRY))) {
-                restart_syscall = 1;
-        } else
-                restart_syscall = 0;
+            (regs->tstate & (TSTATE_XCARRY | TSTATE_ICARRY)))
+                regs->u_regs[UREG_G6] = orig_i0;
 
         if (current_thread_info()->status & TS_RESTORE_SIGMASK)
                 oldset = &current->saved_sigmask;
@@ -542,22 +558,20 @@ static void do_signal(struct pt_regs *regs, unsigned long orig_i0)
 
 #ifdef CONFIG_COMPAT
         if (test_thread_flag(TIF_32BIT)) {
-                extern void do_signal32(sigset_t *, struct pt_regs *,
-                                        int restart_syscall,
-                                        unsigned long orig_i0);
-                do_signal32(oldset, regs, restart_syscall, orig_i0);
+                extern void do_signal32(sigset_t *, struct pt_regs *);
+                do_signal32(oldset, regs);
                 return;
         }
 #endif  
 
         signr = get_signal_to_deliver(&info, &ka, regs, NULL);
 
-        /* If the debugger messes with the program counter, it clears
-         * the software "in syscall" bit, directing us to not perform
-         * a syscall restart.
-         */
-        if (restart_syscall && !pt_regs_is_syscall(regs))
-                restart_syscall = 0;
+        restart_syscall = 0;
+        if (pt_regs_is_syscall(regs) &&
+            (regs->tstate & (TSTATE_XCARRY | TSTATE_ICARRY))) {
+                restart_syscall = 1;
+                orig_i0 = regs->u_regs[UREG_G6];
+        }
 
         if (signr > 0) {
                 if (restart_syscall)