1 files changed, 25 insertions, 5 deletions

diff --git a/arch/sparc/kernel/signal_32.c b/arch/sparc/kernel/signal_32.c
index 8ce247ac04c..d54c6e53aba 100644
--- a/arch/sparc/kernel/signal_32.c
+++ b/arch/sparc/kernel/signal_32.c
@@ -519,10 +519,26 @@ 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->psr & PSR_C))
-                restart_syscall = 1;
-        else
-                restart_syscall = 0;
+                regs->u_regs[UREG_G6] = orig_i0;
 
         if (test_thread_flag(TIF_RESTORE_SIGMASK))
                 oldset = &current->saved_sigmask;
@@ -535,8 +551,12 @@ static void do_signal(struct pt_regs *regs, unsigned long orig_i0)
          * 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->psr & PSR_C)) {
+                restart_syscall = 1;
+                orig_i0 = regs->u_regs[UREG_G6];
+        }
+
 
         if (signr > 0) {
                 if (restart_syscall)