reclaim the memory wasted by dynamic linking for use by malloc
diff --git a/src/ldso/dynlink.c b/src/ldso/dynlink.c
index 527b36b..031e1f0 100644
--- a/src/ldso/dynlink.c
+++ b/src/ldso/dynlink.c
@@ -139,6 +139,37 @@
}
}
+/* 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. */
+
+static void reclaim(unsigned char *base, size_t start, size_t end)
+{
+ size_t *a, *z;
+ 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 = (size_t *)(base + start);
+ z = (size_t *)(base + end);
+ a[-2] = 1;
+ a[-1] = z[0] = end-start + 2*sizeof(size_t) | 1;
+ z[1] = 1;
+ free(a);
+}
+
+static void reclaim_gaps(unsigned char *base, Phdr *ph, size_t phent, size_t phcnt)
+{
+ for (; phcnt--; ph=(void *)((char *)ph+phent)) {
+ if (ph->p_type!=PT_LOAD) continue;
+ if ((ph->p_flags&(PF_R|PF_W))!=(PF_R|PF_W)) continue;
+ reclaim(base, ph->p_vaddr & -PAGE_SIZE, ph->p_vaddr);
+ reclaim(base, ph->p_vaddr+ph->p_memsz,
+ ph->p_vaddr+ph->p_memsz+PAGE_SIZE-1 & -PAGE_SIZE);
+ }
+}
+
static void *map_library(int fd, size_t *lenp, unsigned char **basep, size_t *dynp)
{
Ehdr buf[(896+sizeof(Ehdr))/sizeof(Ehdr)];
@@ -217,6 +248,8 @@
}
}
}
+ if (!runtime) reclaim_gaps(base, (void *)((char *)buf + eh->e_phoff),
+ eh->e_phentsize, eh->e_phnum);
*lenp = map_len;
*basep = base;
*dynp = dyn;
@@ -398,6 +431,7 @@
size_t lib_dyn[DYN_CNT] = {0};
size_t i;
Phdr *phdr;
+ Ehdr *ehdr;
struct dso lib, app;
/* Find aux vector just past environ[] */
@@ -456,6 +490,11 @@
/* At this point the standard library is fully functional */
+ reclaim_gaps(app.base, (void *)aux[AT_PHDR], aux[AT_PHENT], aux[AT_PHNUM]);
+ ehdr = (void *)lib.base;
+ reclaim_gaps(lib.base, (void *)(lib.base+ehdr->e_phoff),
+ ehdr->e_phentsize, ehdr->e_phnum);
+
head = tail = &app;
libc = &lib;
app.next = 0;