diff --git a/arch/sparc64/kernel/etrap.S b/arch/sparc64/kernel/etrap.S
index 4b2bf9eb447a..b49d3b60bc0c 100644
--- a/arch/sparc64/kernel/etrap.S
+++ b/arch/sparc64/kernel/etrap.S
@@ -53,7 +53,11 @@ etrap_irq:
 		stx	%g3, [%g2 + STACKFRAME_SZ + PT_V9_TPC]
 		rd	%y, %g3
 		stx	%g1, [%g2 + STACKFRAME_SZ + PT_V9_TNPC]
+		rdpr	%tt, %g1
 		st	%g3, [%g2 + STACKFRAME_SZ + PT_V9_Y]
+		sethi	%hi(PT_REGS_MAGIC), %g3
+		or	%g3, %g1, %g1
+		st	%g1, [%g2 + STACKFRAME_SZ + PT_V9_MAGIC]
 
 		rdpr	%cansave, %g1
 		brnz,pt %g1, etrap_save
diff --git a/include/asm-sparc64/ptrace.h b/include/asm-sparc64/ptrace.h
index 6da197803efc..b4b951d570bb 100644
--- a/include/asm-sparc64/ptrace.h
+++ b/include/asm-sparc64/ptrace.h
@@ -8,6 +8,8 @@
  * stack during a system call and basically all traps.
  */
 
+#define PT_REGS_MAGIC 0x57ac6c00
+
 #ifndef __ASSEMBLY__
 
 struct pt_regs {
@@ -16,7 +18,19 @@ struct pt_regs {
 	unsigned long tpc;
 	unsigned long tnpc;
 	unsigned int y;
-	unsigned int fprs;
+
+	/* We encode a magic number, PT_REGS_MAGIC, along
+	 * with the %tt (trap type) register value at trap
+	 * entry time.  The magic number allows us to identify
+	 * accurately a trap stack frame in the stack
+	 * unwinder, and the %tt value allows us to test
+	 * things like "in a system call" etc. for an arbitray
+	 * process.
+	 *
+	 * The PT_REGS_MAGIC is choosen such that it can be
+	 * loaded completely using just a sethi instruction.
+	 */
+	unsigned int magic;
 };
 
 struct pt_regs32 {
@@ -147,7 +161,7 @@ extern void __show_regs(struct pt_regs *);
 #define PT_V9_TPC    0x88
 #define PT_V9_TNPC   0x90
 #define PT_V9_Y      0x98
-#define PT_V9_FPRS   0x9c
+#define PT_V9_MAGIC  0x9c
 #define PT_TSTATE	PT_V9_TSTATE
 #define PT_TPC		PT_V9_TPC
 #define PT_TNPC		PT_V9_TNPC