add glue code for mallocng merge

this includes both an implementation of reclaimed-gap donation from
ldso and a version of mallocng's glue.h with namespace-safe linkage to
underlying syscalls, integration with AT_RANDOM initialization, and
internal locking that's optimized out when the process is
single-threaded.

1 files changed, 39 insertions, 0 deletions

diff --git a/src/malloc/mallocng/donate.c b/src/malloc/mallocng/donate.c
new file mode 100644
index 00000000..41d850f3
--- /dev/null
+++ b/src/malloc/mallocng/donate.c
@@ -0,0 +1,39 @@
+#include <stdlib.h>
+#include <stdint.h>
+#include <limits.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <errno.h>
+
+#include "meta.h"
+
+static void donate(unsigned char *base, size_t len)
+{
+	uintptr_t a = (uintptr_t)base;
+	uintptr_t b = a + len;
+	a += -a & (UNIT-1);
+	b -= b & (UNIT-1);
+	memset(base, 0, len);
+	for (int sc=47; sc>0 && b>a; sc-=4) {
+		if (b-a < (size_classes[sc]+1)*UNIT) continue;
+		struct meta *m = alloc_meta();
+		m->avail_mask = 0;
+		m->freed_mask = 1;
+		m->mem = (void *)a;
+		m->mem->meta = m;
+		m->last_idx = 0;
+		m->freeable = 0;
+		m->sizeclass = sc;
+		m->maplen = 0;
+		*((unsigned char *)m->mem+UNIT-4) = 0;
+		*((unsigned char *)m->mem+UNIT-3) = 255;
+		m->mem->storage[size_classes[sc]*UNIT-4] = 0;
+		queue(&ctx.active[sc], m);
+		a += (size_classes[sc]+1)*UNIT;
+	}
+}
+
+void __malloc_donate(char *start, char *end)
+{
+	donate((void *)start, end-start);
+}