diff --git a/src/cmd/internal/obj/x86/a.out.go b/src/cmd/internal/obj/x86/a.out.go
index 3be4b59da4..b121f6df7b 100644
--- a/src/cmd/internal/obj/x86/a.out.go
+++ b/src/cmd/internal/obj/x86/a.out.go
@@ -258,23 +258,25 @@ const (
 	REG_DR = REG_DR0
 	REG_TR = REG_TR0
 
-	REGARG   = -1
-	REGRET   = REG_AX
-	FREGRET  = REG_X0
-	REGSP    = REG_SP
-	REGCTXT  = REG_DX
-	REGG     = REG_R14     // g register in ABIInternal
-	REGEXT   = REG_R15     // compiler allocates external registers R15 down
-	FREGMIN  = REG_X0 + 5  // first register variable
-	FREGEXT  = REG_X0 + 15 // first external register
-	T_TYPE   = 1 << 0
-	T_INDEX  = 1 << 1
-	T_OFFSET = 1 << 2
-	T_FCONST = 1 << 3
-	T_SYM    = 1 << 4
-	T_SCONST = 1 << 5
-	T_64     = 1 << 6
-	T_GOTYPE = 1 << 7
+	REGARG       = -1
+	REGRET       = REG_AX
+	FREGRET      = REG_X0
+	REGSP        = REG_SP
+	REGCTXT      = REG_DX
+	REGENTRYTMP0 = REG_R12     // scratch register available at function entry in ABIInternal
+	REGENTRYTMP1 = REG_R13     // scratch register available at function entry in ABIInternal
+	REGG         = REG_R14     // g register in ABIInternal
+	REGEXT       = REG_R15     // compiler allocates external registers R15 down
+	FREGMIN      = REG_X0 + 5  // first register variable
+	FREGEXT      = REG_X0 + 15 // first external register
+	T_TYPE       = 1 << 0
+	T_INDEX      = 1 << 1
+	T_OFFSET     = 1 << 2
+	T_FCONST     = 1 << 3
+	T_SYM        = 1 << 4
+	T_SCONST     = 1 << 5
+	T_64         = 1 << 6
+	T_GOTYPE     = 1 << 7
 )
 
 // https://www.uclibc.org/docs/psABI-x86_64.pdf, figure 3.36
diff --git a/src/cmd/internal/obj/x86/obj6.go b/src/cmd/internal/obj/x86/obj6.go
index 2fbeaad572..a314583e49 100644
--- a/src/cmd/internal/obj/x86/obj6.go
+++ b/src/cmd/internal/obj/x86/obj6.go
@@ -658,6 +658,12 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 			p = load_g(ctxt, p, newprog, regg) // load g into regg
 		}
 	}
+	var regEntryTmp0, regEntryTmp1 int16
+	if ctxt.Arch.Family == sys.AMD64 {
+		regEntryTmp0, regEntryTmp1 = REGENTRYTMP0, REGENTRYTMP1
+	} else {
+		regEntryTmp0, regEntryTmp1 = REG_BX, REG_DI
+	}
 
 	if !cursym.Func().Text.From.Sym.NoSplit() {
 		p = stacksplit(ctxt, cursym, p, newprog, autoffset, int32(textarg), regg) // emit split check
@@ -712,17 +718,17 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 		//   g._panic.argp = bottom-of-frame
 		// }
 		//
-		//	MOVQ g_panic(g), BX
-		//	TESTQ BX, BX
+		//	MOVQ g_panic(g), regEntryTmp0
+		//	TESTQ regEntryTmp0, regEntryTmp0
 		//	JNE checkargp
 		// end:
 		//	NOP
 		//  ... rest of function ...
 		// checkargp:
-		//	LEAQ (autoffset+8)(SP), DI
-		//	CMPQ panic_argp(BX), DI
+		//	LEAQ (autoffset+8)(SP), regEntryTmp1
+		//	CMPQ panic_argp(regEntryTmp0), regEntryTmp1
 		//	JNE end
-		//  MOVQ SP, panic_argp(BX)
+		//  MOVQ SP, panic_argp(regEntryTmp0)
 		//  JMP end
 		//
 		// The NOP is needed to give the jumps somewhere to land.
@@ -731,25 +737,25 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 		// The layout is chosen to help static branch prediction:
 		// Both conditional jumps are unlikely, so they are arranged to be forward jumps.
 
-		// MOVQ g_panic(CX), BX
+		// MOVQ g_panic(g), regEntryTmp0
 		p = obj.Appendp(p, newprog)
 		p.As = AMOVQ
 		p.From.Type = obj.TYPE_MEM
 		p.From.Reg = regg
 		p.From.Offset = 4 * int64(ctxt.Arch.PtrSize) // g_panic
 		p.To.Type = obj.TYPE_REG
-		p.To.Reg = REG_BX
+		p.To.Reg = regEntryTmp0
 		if ctxt.Arch.Family == sys.I386 {
 			p.As = AMOVL
 		}
 
-		// TESTQ BX, BX
+		// TESTQ regEntryTmp0, regEntryTmp0
 		p = obj.Appendp(p, newprog)
 		p.As = ATESTQ
 		p.From.Type = obj.TYPE_REG
-		p.From.Reg = REG_BX
+		p.From.Reg = regEntryTmp0
 		p.To.Type = obj.TYPE_REG
-		p.To.Reg = REG_BX
+		p.To.Reg = regEntryTmp0
 		if ctxt.Arch.Family == sys.I386 {
 			p.As = ATESTL
 		}
@@ -769,14 +775,14 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 		for last = end; last.Link != nil; last = last.Link {
 		}
 
-		// LEAQ (autoffset+8)(SP), DI
+		// LEAQ (autoffset+8)(SP), regEntryTmp1
 		p = obj.Appendp(last, newprog)
 		p.As = ALEAQ
 		p.From.Type = obj.TYPE_MEM
 		p.From.Reg = REG_SP
 		p.From.Offset = int64(autoffset) + int64(ctxt.Arch.RegSize)
 		p.To.Type = obj.TYPE_REG
-		p.To.Reg = REG_DI
+		p.To.Reg = regEntryTmp1
 		if ctxt.Arch.Family == sys.I386 {
 			p.As = ALEAL
 		}
@@ -784,14 +790,14 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 		// Set jne branch target.
 		jne.To.SetTarget(p)
 
-		// CMPQ panic_argp(BX), DI
+		// CMPQ panic_argp(regEntryTmp0), regEntryTmp1
 		p = obj.Appendp(p, newprog)
 		p.As = ACMPQ
 		p.From.Type = obj.TYPE_MEM
-		p.From.Reg = REG_BX
+		p.From.Reg = regEntryTmp0
 		p.From.Offset = 0 // Panic.argp
 		p.To.Type = obj.TYPE_REG
-		p.To.Reg = REG_DI
+		p.To.Reg = regEntryTmp1
 		if ctxt.Arch.Family == sys.I386 {
 			p.As = ACMPL
 		}
@@ -802,13 +808,13 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 		p.To.Type = obj.TYPE_BRANCH
 		p.To.SetTarget(end)
 
-		// MOVQ SP, panic_argp(BX)
+		// MOVQ SP, panic_argp(regEntryTmp0)
 		p = obj.Appendp(p, newprog)
 		p.As = AMOVQ
 		p.From.Type = obj.TYPE_REG
 		p.From.Reg = REG_SP
 		p.To.Type = obj.TYPE_MEM
-		p.To.Reg = REG_BX
+		p.To.Reg = regEntryTmp0
 		p.To.Offset = 0 // Panic.argp
 		if ctxt.Arch.Family == sys.I386 {
 			p.As = AMOVL