From ebf85fb7b75f0bdc3cb27693641bc34c11ca7bed Mon Sep 17 00:00:00 2001
From: cinap_lenrek <cinap_lenrek@felloff.net>
Date: Wed, 1 Apr 2015 01:30:16 +0200
Subject: vl: prevent stack altering instructions to be hoisted above loads

fixes bug with libmemdraw where the linker would hoist
the final ADD $const, SP at the end over loads from the
stack causing the front to fall off once a interrupt hits.
---
 sys/src/cmd/vl/sched.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/sys/src/cmd/vl/sched.c b/sys/src/cmd/vl/sched.c
index efa88a755..7537cf1c6 100644
--- a/sys/src/cmd/vl/sched.c
+++ b/sys/src/cmd/vl/sched.c
@@ -85,7 +85,7 @@ sched(Prog *p0, Prog *pe)
 		for(t=s+1; t<=se; t++) {
 			if(!(t->p.mark & LOAD))
 				continue;
-			if(t->p.mark & BRANCH)
+			if(t->p.mark & BRANCH || t->set.ireg & (1<<REGSP))
 				break;
 			if(conflict(s, t))
 				break;
@@ -102,7 +102,7 @@ sched(Prog *p0, Prog *pe)
 
 		/* put schedule fodder above load */
 		for(t=s+1; t<=se; t++) {
-			if(t->p.mark & BRANCH)
+			if(t->p.mark & BRANCH || t->set.ireg & (1<<REGSP))
 				break;
 			if(s > sch && conflict(s-1, t))
 				continue;
@@ -634,7 +634,6 @@ offoverlap(Sch *sa, Sch *sb)
 int
 conflict(Sch *sa, Sch *sb)
 {
-
 	if(sa->set.ireg & sb->used.ireg)
 		return 1;
 	if(sa->set.freg & sb->used.freg)
-- 
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