From: Russ Cox <rsc@golang.org>
Date: Sat, 22 Dec 2012 16:20:17 +0000 (-0500)
Subject: cmd/6l, cmd/8l: add -Z flag to zero stack frame on entry
X-Git-Tag: go1.1rc2~1556
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=b9da27bed238b5bc55f0f92ed60dc691bd4691f5;p=gostls13.git

cmd/6l, cmd/8l: add -Z flag to zero stack frame on entry

Replacement for GOEXPERIMENT=zerostack, easier to use.
Does not require a separate toolchain.

R=ken2
CC=golang-dev
https://golang.org/cl/6996051
---

diff --git a/src/cmd/6l/pass.c b/src/cmd/6l/pass.c
index 043048e8a0..0054b329f4 100644
--- a/src/cmd/6l/pass.c
+++ b/src/cmd/6l/pass.c
@@ -653,6 +653,34 @@ dostkoff(void)
 			q1->pcond = p;
 		}
 		
+		if(debug['Z'] && autoffset && !(cursym->text->from.scale&NOSPLIT)) {
+			// 6l -Z means zero the stack frame on entry.
+			// This slows down function calls but can help avoid
+			// false positives in garbage collection.
+			p = appendp(p);
+			p->as = AMOVQ;
+			p->from.type = D_SP;
+			p->to.type = D_DI;
+			
+			p = appendp(p);
+			p->as = AMOVQ;
+			p->from.type = D_CONST;
+			p->from.offset = autoffset/8;
+			p->to.type = D_CX;
+			
+			p = appendp(p);
+			p->as = AMOVQ;
+			p->from.type = D_CONST;
+			p->from.offset = 0;
+			p->to.type = D_AX;
+			
+			p = appendp(p);
+			p->as = AREP;
+			
+			p = appendp(p);
+			p->as = ASTOSQ;
+		}
+		
 		for(; p != P; p = p->link) {
 			pcsize = p->mode/8;
 			a = p->from.type;
diff --git a/src/cmd/8l/pass.c b/src/cmd/8l/pass.c
index 6cf3009e2c..03292a5b3f 100644
--- a/src/cmd/8l/pass.c
+++ b/src/cmd/8l/pass.c
@@ -593,6 +593,34 @@ dostkoff(void)
 		}
 		deltasp = autoffset;
 		
+		if(debug['Z'] && autoffset && !(cursym->text->from.scale&NOSPLIT)) {
+			// 8l -Z means zero the stack frame on entry.
+			// This slows down function calls but can help avoid
+			// false positives in garbage collection.
+			p = appendp(p);
+			p->as = AMOVL;
+			p->from.type = D_SP;
+			p->to.type = D_DI;
+			
+			p = appendp(p);
+			p->as = AMOVL;
+			p->from.type = D_CONST;
+			p->from.offset = autoffset/4;
+			p->to.type = D_CX;
+			
+			p = appendp(p);
+			p->as = AMOVL;
+			p->from.type = D_CONST;
+			p->from.offset = 0;
+			p->to.type = D_AX;
+			
+			p = appendp(p);
+			p->as = AREP;
+			
+			p = appendp(p);
+			p->as = ASTOSL;
+		}
+		
 		for(; p != P; p = p->link) {
 			a = p->from.type;
 			if(a == D_AUTO)