diff -ur 2.5.old/arch/ppc/kernel/misc.S 2.5/arch/ppc/kernel/misc.S
--- 2.5.old/arch/ppc/kernel/misc.S	2003-12-15 11:20:44.000000000 -0600
+++ 2.5/arch/ppc/kernel/misc.S	2003-12-14 21:31:49.000000000 -0600
@@ -1385,3 +1385,5 @@
 	.long sys_statfs64
 	.long sys_fstatfs64
 	.long ppc_fadvise64_64
+	.long sys_ni_syscall	/* 255 */
+	.long sys_debug_setcontext
diff -ur 2.5.old/arch/ppc/kernel/signal.c 2.5/arch/ppc/kernel/signal.c
--- 2.5.old/arch/ppc/kernel/signal.c	2003-12-15 11:21:16.000000000 -0600
+++ 2.5/arch/ppc/kernel/signal.c	2003-12-17 07:50:15.000000000 -0600
@@ -445,6 +445,88 @@
 	return 0;
 }

+int sys_debug_setcontext(struct ucontext __user *ctx,
+			 int ndbg, struct sig_dbg_op *dbg,
+			 int r6, int r7, int r8,
+			 struct pt_regs *regs)
+{
+	unsigned char tmp;
+	struct sig_dbg_op op;
+	int i;
+	unsigned long new_msr = regs->msr;
+#if defined(CONFIG_4xx)
+	unsigned long new_dbcr0 = current->thread.dbcr0;
+#endif
+
+	for (i=0; i<ndbg; i++) {
+		if (__copy_from_user(&op, dbg, sizeof(op)))
+			return -EFAULT;
+		switch (op.dbg_type) {
+		case SIG_DBG_SINGLE_STEPPING:
+#if defined(CONFIG_4xx)
+			if (op.dbg_value) {
+				new_msr |= MSR_DE;
+				new_dbcr0 |= (DBCR0_IDM | DBCR0_IC);
+			} else {
+				new_msr &= ~MSR_DE;
+				new_dbcr0 &= ~(DBCR0_IDM | DBCR0_IC);
+			}
+#else
+			if (op.dbg_value)
+				new_msr |= MSR_SE;
+			else
+				new_msr &= ~MSR_SE;
+#endif
+			break;
+		case SIG_DBG_BRANCH_TRACING:
+#if defined(CONFIG_4xx)
+			return -EINVAL;
+#else
+			if (op.dbg_value)
+				new_msr |= MSR_BE;
+			else
+				new_msr &= ~MSR_BE;
+#endif
+			break;
+
+		default:
+			return -EINVAL;
+		}
+	}
+
+	if (verify_area(VERIFY_READ, ctx, sizeof(*ctx))
+	    || __get_user(tmp, (u8 *) ctx)
+	    || __get_user(tmp, (u8 *) (ctx + 1) - 1))
+		return -EFAULT;
+
+	/* We wait until here to actually install the values in the
+	   registers so if we fail in the above loop, it will not
+	   affect the contents of these registers.  After this point,
+	   failure is a problem, anyway, and it's very unlikely unless
+	   the user is really doing something wrong. */
+	regs->msr = new_msr;
+#if defined(CONFIG_4xx)
+	current->thread.dbcr0 = new_dbcr0;
+#endif
+
+	/*
+	 * If we get a fault copying the context into the kernel's
+	 * image of the user's registers, we can't just return -EFAULT
+	 * because the user's registers will be corrupted.  For instance
+	 * the NIP value may have been updated but not some of the
+	 * other registers.  Given that we have done the verify_area
+	 * and successfully read the first and last bytes of the region
+	 * above, this should only happen in an out-of-memory situation
+	 * or if another thread unmaps the region containing the context.
+	 * We kill the task with a SIGSEGV in this situation.
+	 */
+	if (do_setcontext(ctx, regs))
+		do_exit(SIGSEGV);
+	sigreturn_exit(regs);
+	/* doesn't actually return back to here */
+	return 0;
+}
+
 /*
  * OK, we're invoking a handler
  */
diff -ur 2.5.old/arch/ppc/kernel/traps.c 2.5/arch/ppc/kernel/traps.c
--- 2.5.old/arch/ppc/kernel/traps.c	2003-12-15 11:18:41.000000000 -0600
+++ 2.5/arch/ppc/kernel/traps.c	2003-12-14 21:27:33.000000000 -0600
@@ -462,7 +462,7 @@
 void
 SingleStepException(struct pt_regs *regs)
 {
-	regs->msr &= ~MSR_SE;  /* Turn off 'trace' bit */
+	regs->msr &= ~(MSR_SE | MSR_BE);  /* Turn off 'trace' bits */
 	if (debugger_sstep(regs))
 		return;
 	_exception(SIGTRAP, regs, TRAP_TRACE, 0);
diff -ur 2.5.old/include/asm-ppc/signal.h 2.5/include/asm-ppc/signal.h
--- 2.5.old/include/asm-ppc/signal.h	2003-12-15 11:18:33.000000000 -0600
+++ 2.5/include/asm-ppc/signal.h	2003-12-14 21:27:40.000000000 -0600
@@ -153,4 +153,23 @@
 #define ptrace_signal_deliver(regs, cookie) do { } while (0)
 #endif /* __KERNEL__ */

+/*
+ * These are parameters to dbg_sigreturn syscall.  They enable or
+ * disable certain debugging things that can be done from signal
+ * handlers.  The dbg_sigreturn syscall *must* be called from a
+ * SA_SIGINFO signal so the ucontext can be passed to it.  It takes an
+ * array of struct sig_dbg_op, which has the debug operations to
+ * perform before returning from the signal.
+ */
+struct sig_dbg_op {
+	int dbg_type;
+	unsigned long dbg_value;
+};
+
+/* Enable or disable single-stepping.  The value sets the state. */
+#define SIG_DBG_SINGLE_STEPPING		1
+
+/* Enable or disable branch tracing.  The value sets the state. */
+#define SIG_DBG_BRANCH_TRACING		2
+
 #endif
diff -ur 2.5.old/include/asm-ppc/unistd.h 2.5/include/asm-ppc/unistd.h
--- 2.5.old/include/asm-ppc/unistd.h	2003-12-15 11:18:41.000000000 -0600
+++ 2.5/include/asm-ppc/unistd.h	2003-12-14 21:29:24.000000000 -0600
@@ -259,8 +259,9 @@
 #define __NR_statfs64		252
 #define __NR_fstatfs64		253
 #define __NR_fadvise64_64	254
+#define __NR_debug_setcontext	256

-#define __NR_syscalls		255
+#define __NR_syscalls		257

 #define __NR(n)	#n