sh: Remove linked list of stack marks.

The linked list of stack marks may cause problems if the allocation stack is
used between an exception and a higher-level popstackmark(), as it may then
touch a stack mark that is local to a function which has returned.

Also, the adjustment compares to a pointer passed to realloc(), which is
undefined behaviour.

Instead of adjusting stack marks when reallocating stack blocks, ensure that
such an adjustment is never necessary by fixing a small piece of memory in
place at a stack mark. This also simplifies the code.

To avoid the problems reported in bin/175922, it remains necessary to call
setstackmark() after popstackmark() if the stack mark remains in use.

2 files changed, 3 insertions, 18 deletions

diff --git a/bin/sh/memalloc.c b/bin/sh/memalloc.c
index f33a15c..cb330d0 100644
--- a/bin/sh/memalloc.c
+++ b/bin/sh/memalloc.c
@@ -124,7 +124,6 @@ struct stack_block {
 #define SPACE(sp)	((char*)(sp) + ALIGN(sizeof(struct stack_block)))
 
 static struct stack_block *stackp;
-static struct stackmark *markp;
 char *stacknxt;
 int stacknleft;
 char *sstrend;
@@ -186,8 +185,9 @@ setstackmark(struct stackmark *mark)
 	mark->stackp = stackp;
 	mark->stacknxt = stacknxt;
 	mark->stacknleft = stacknleft;
-	mark->marknext = markp;
-	markp = mark;
+	/* Ensure this block stays in place. */
+	if (stackp != NULL && stacknxt == SPACE(stackp))
+		stalloc(1);
 }
 
 
@@ -197,7 +197,6 @@ popstackmark(struct stackmark *mark)
 	struct stack_block *sp;
 
 	INTOFF;
-	markp = mark->marknext;
 	while (stackp != mark->stackp) {
 		sp = stackp;
 		stackp = sp->prev;
@@ -229,7 +228,6 @@ growstackblock(int min)
 	int oldlen;
 	struct stack_block *sp;
 	struct stack_block *oldstackp;
-	struct stackmark *xmark;
 
 	if (min < stacknleft)
 		min = stacknleft;
@@ -254,18 +252,6 @@ growstackblock(int min)
 		stacknxt = SPACE(sp);
 		stacknleft = newlen - (stacknxt - (char*)sp);
 		sstrend = stacknxt + stacknleft;
-
-		/*
-		 * Stack marks pointing to the start of the old block
-		 * must be relocated to point to the new block
-		 */
-		xmark = markp;
-		while (xmark != NULL && xmark->stackp == oldstackp) {
-			xmark->stackp = stackp;
-			xmark->stacknxt = stacknxt;
-			xmark->stacknleft = stacknleft;
-			xmark = xmark->marknext;
-		}
 		INTON;
 	} else {
 		newlen -= ALIGN(sizeof(struct stack_block));
diff --git a/bin/sh/memalloc.h b/bin/sh/memalloc.h
index 95a6594..a22fa39 100644
--- a/bin/sh/memalloc.h
+++ b/bin/sh/memalloc.h
@@ -39,7 +39,6 @@ struct stackmark {
 	struct stack_block *stackp;
 	char *stacknxt;
 	int stacknleft;
-        struct stackmark *marknext;
 };