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Use mmap with a hint rather than sbrk for allocating executable memory within 32-bit displacement range of compiled code
author Michael Pavone <pavone@retrodev.com>
date Sun, 28 Jun 2015 10:12:37 -0700
parents 140af5509ce7
children c47e1750c264
comparison
equal deleted inserted replaced
757:483f7e7926a6 758:b52cd6854c28
6 #include <sys/mman.h> 6 #include <sys/mman.h>
7 #include <stddef.h> 7 #include <stddef.h>
8 #include <stdint.h> 8 #include <stdint.h>
9 #include <stdlib.h> 9 #include <stdlib.h>
10 #include <unistd.h> 10 #include <unistd.h>
11
11 #include "mem.h" 12 #include "mem.h"
12 13 #ifndef MAP_ANONYMOUS
13 /* 14 #define MAP_ANONYMOUS MAP_ANON
14 void * alloc_code(size_t *size) 15 #endif
15 {
16 *size += PAGE_SIZE - (*size & (PAGE_SIZE - 1));
17 return mmap(NULL, *size, PROT_EXEC | PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
18 }
19 */
20
21 /*
22 void * alloc_code(size_t *size)
23 {
24 char * ret = malloc(*size);
25 char * base = (char *)(((intptr_t)ret) & (~(PAGE_SIZE-1)));
26 mprotect(base, (ret + *size) - base, PROT_EXEC | PROT_READ | PROT_WRITE);
27 return ret;
28 }
29 */
30 16
31 void * alloc_code(size_t *size) 17 void * alloc_code(size_t *size)
32 { 18 {
19 //start at the 1GB mark to allow plenty of room for sbrk based malloc implementations
20 //while still keeping well within 32-bit displacement range for calling code compiled into the executable
21 static uint8_t *next = (uint8_t *)0x40000000;
33 *size += PAGE_SIZE - (*size & (PAGE_SIZE - 1)); 22 *size += PAGE_SIZE - (*size & (PAGE_SIZE - 1));
34 void * ret = sbrk(*size); 23 uint8_t *ret = mmap(NULL, *size, PROT_EXEC | PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
35 if (ret == ((void *)-1)) { 24 next = ret + *size;
36 return NULL;
37 }
38 mprotect(ret, *size, PROT_EXEC | PROT_READ | PROT_WRITE);
39 return ret; 25 return ret;
40 } 26 }
27