# HG changeset patch
# User Michael Pavone <pavone@retrodev.com>
# Date 1435511557 25200
# Node ID b52cd6854c28c527f7e31c6a78f1543a0846532e
# Parent  483f7e7926a6130f9c0c30b3f12b90747e31093b
Use mmap with a hint rather than sbrk for allocating executable memory within 32-bit displacement range of compiled code

diff -r 483f7e7926a6 -r b52cd6854c28 mem.c
--- a/mem.c	Sun Jun 28 09:53:17 2015 -0700
+++ b/mem.c	Sun Jun 28 10:12:37 2015 -0700
@@ -8,33 +8,20 @@
 #include <stdint.h>
 #include <stdlib.h>
 #include <unistd.h>
+
 #include "mem.h"
-
-/*
-void * alloc_code(size_t *size)
-{
-	*size += PAGE_SIZE - (*size & (PAGE_SIZE - 1));
-	return mmap(NULL, *size, PROT_EXEC | PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
-}
-*/
-
-/*
-void * alloc_code(size_t *size)
-{
-	char * ret = malloc(*size);
-	char * base = (char *)(((intptr_t)ret) & (~(PAGE_SIZE-1)));
-	mprotect(base, (ret + *size) - base, PROT_EXEC | PROT_READ | PROT_WRITE);
-	return ret;
-}
-*/
+#ifndef MAP_ANONYMOUS
+#define MAP_ANONYMOUS MAP_ANON
+#endif
 
 void * alloc_code(size_t *size)
 {
+	//start at the 1GB mark to allow plenty of room for sbrk based malloc implementations
+	//while still keeping well within 32-bit displacement range for calling code compiled into the executable
+	static uint8_t *next = (uint8_t *)0x40000000;
 	*size += PAGE_SIZE - (*size & (PAGE_SIZE - 1));
-	void * ret = sbrk(*size);
-	if (ret == ((void *)-1)) {
-		return NULL;
-	}
-	mprotect(ret, *size, PROT_EXEC | PROT_READ | PROT_WRITE);
+	uint8_t *ret = mmap(NULL, *size, PROT_EXEC | PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+	next = ret + *size;
 	return ret;
 }
+