ldso, malloc: implement reclaim_gaps via __malloc_donate

Split 'free' into unmap_chunk and bin_chunk, use the latter to introduce
__malloc_donate and use it in reclaim_gaps instead of calling 'free'.

diff --git a/ldso/dynlink.c b/ldso/dynlink.c
index 9bf6924..b9ff41b 100644 (file)
--- a/ldso/dynlink.c
+++ b/ldso/dynlink.c
@@ -476,23 +476,15 @@ static void redo_lazy_relocs()
 /* A huge hack: to make up for the wastefulness of shared libraries
  * needing at least a page of dirty memory even if they have no global
  * data, we reclaim the gaps at the beginning and end of writable maps
- * and "donate" them to the heap by setting up minimal malloc
- * structures and then freeing them. */
+ * and "donate" them to the heap. */
 
 static void reclaim(struct dso *dso, size_t start, size_t end)
 {
-       size_t *a, *z;
+       void __malloc_donate(char *, char *);
        if (start >= dso->relro_start && start < dso->relro_end) start = dso->relro_end;
        if (end   >= dso->relro_start && end   < dso->relro_end) end = dso->relro_start;
-       start = start + 6*sizeof(size_t)-1 & -4*sizeof(size_t);
-       end = (end & -4*sizeof(size_t)) - 2*sizeof(size_t);
-       if (start>end || end-start < 4*sizeof(size_t)) return;
-       a = laddr(dso, start);
-       z = laddr(dso, end);
-       a[-2] = 1;
-       a[-1] = z[0] = end-start + 2*sizeof(size_t) | 1;
-       z[1] = 1;
-       free(a);
+       if (start >= end) return;
+       __malloc_donate(laddr(dso, start), laddr(dso, end));
 }
 
 static void reclaim_gaps(struct dso *dso)

diff --git a/src/malloc/malloc.c b/src/malloc/malloc.c
index db19bc3..6605ec3 100644 (file)
--- a/src/malloc/malloc.c
+++ b/src/malloc/malloc.c
@@ -299,6 +299,8 @@ static int pretrim(struct chunk *self, size_t n, int i, int j)
        return 1;
 }
 
+static void bin_chunk(struct chunk *);
+
 static void trim(struct chunk *self, size_t n)
 {
        size_t n1 = CHUNK_SIZE(self);
@@ -314,7 +316,7 @@ static void trim(struct chunk *self, size_t n)
        next->psize = n1-n | C_INUSE;
        self->csize = n | C_INUSE;
 
-       free(CHUNK_TO_MEM(split));
+       bin_chunk(split);
 }
 
 void *malloc(size_t n)
@@ -465,29 +467,14 @@ copy_free_ret:
        return new;
 }
 
-void free(void *p)
+static void bin_chunk(struct chunk *self)
 {
-       struct chunk *self, *next;
+       struct chunk *next = NEXT_CHUNK(self);
        size_t final_size, new_size, size;
        int reclaim=0;
        int i;
 
-       if (!p) return;
-
-       self = MEM_TO_CHUNK(p);
-
-       if (IS_MMAPPED(self)) {
-               size_t extra = self->psize;
-               char *base = (char *)self - extra;
-               size_t len = CHUNK_SIZE(self) + extra;
-               /* Crash on double free */
-               if (extra & 1) a_crash();
-               __munmap(base, len);
-               return;
-       }
-
        final_size = new_size = CHUNK_SIZE(self);
-       next = NEXT_CHUNK(self);
 
        /* Crash on corrupted footer (likely from buffer overflow) */
        if (next->psize != self->csize) a_crash();
@@ -548,3 +535,41 @@ void free(void *p)
 
        unlock_bin(i);
 }
+
+static void unmap_chunk(struct chunk *self)
+{
+       size_t extra = self->psize;
+       char *base = (char *)self - extra;
+       size_t len = CHUNK_SIZE(self) + extra;
+       /* Crash on double free */
+       if (extra & 1) a_crash();
+       __munmap(base, len);
+}
+
+void free(void *p)
+{
+       if (!p) return;
+
+       struct chunk *self = MEM_TO_CHUNK(p);
+
+       if (IS_MMAPPED(self))
+               unmap_chunk(self);
+       else
+               bin_chunk(self);
+}
+
+void __malloc_donate(char *start, char *end)
+{
+       size_t align_start_up = (SIZE_ALIGN-1) & (-(uintptr_t)start - OVERHEAD);
+       size_t align_end_down = (SIZE_ALIGN-1) & (uintptr_t)end;
+
+       if (end - start <= OVERHEAD + align_start_up + align_end_down)
+               return;
+       start += align_start_up + OVERHEAD;
+       end   -= align_end_down;
+
+       struct chunk *c = MEM_TO_CHUNK(start), *n = MEM_TO_CHUNK(end);
+       c->psize = n->csize = C_INUSE;
+       c->csize = n->psize = C_INUSE | (end-start);
+       bin_chunk(c);
+}