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libc: Readjust freep realloc() modifies the free list

Freep can be pointing to the block that is modified by
realloc(), so it is needed to set freep to some valid
value (the actual value is not important).

--- a/src/libc/stdlib/malloc.c

+++ b/src/libc/stdlib/malloc.c

@@ -13,7 +13,7 @@

 #define ERRADDR ((char *)-1)

 static Header base = { .h.next = &base };

-static Header *freep = &base;

+Header *_freep = &base;

 /*

  * Run over the free list looking for the nearest previous

@@ -25,7 +25,7 @@

 {

 	Header *p;

-	for (p = freep; ;p = p->h.next) {

+	for (p = _freep; ;p = p->h.next) {

 		/* hp between p and p->h.next? */

 		if (p < hp && hp < p->h.next)

 			break;

@@ -69,7 +69,7 @@

 		prev->h.next = hp;

 	}

-	freep = prev;

+	_freep = prev;

 }

 static void *

@@ -112,7 +112,7 @@

 	/* integrate new memory into the list */

 	free(hp + 1);

-	return freep;

+	return _freep;

 }

 /*

@@ -142,7 +142,7 @@

 	/* 1 unit for header plus enough units to fit nbytes */

 	nunits = (nbytes+sizeof(Header)-1)/sizeof(Header) + 1;

-	for (prev = freep; ; prev = cur) {

+	for (prev = _freep; ; prev = cur) {

 		cur = prev->h.next;

 		if (cur->h.size >= nunits) {

 			if (cur->h.size == nunits) {

@@ -154,12 +154,12 @@

 			}

 			cur->h.next = NULL;

-			freep = prev;

+			_freep = prev;

 			return cur + 1;

 		}

-		if (cur == freep) {

+		if (cur == _freep) {

 			if ((cur = morecore(nunits)) == NULL)

 				return NULL;

 		}

--- a/src/libc/stdlib/malloc.h

+++ b/src/libc/stdlib/malloc.h

@@ -12,3 +12,5 @@

 };

 extern void *_prevchunk(Header *);

+

+extern Header *_freep;

--- a/src/libc/stdlib/realloc.c

+++ b/src/libc/stdlib/realloc.c

@@ -53,6 +53,7 @@

 			prev->h.next = new;

 			new->h.next = next->h.next;

 			new->h.size = avail - nunits;

+			_freep = new;

 			return ptr;

 		}

 	}