| 1 |
/* |
| 2 |
* lowmem.c - enable access to low memory globals on Darwin |
| 3 |
* |
| 4 |
* Copyright (c) 2003 Michael Z. Sliczniak |
| 5 |
* |
| 6 |
* Basilisk II (C) 1997-2005 Christian Bauer |
| 7 |
* |
| 8 |
* This program is free software; you can redistribute it and/or modify |
| 9 |
* it under the terms of the GNU General Public License as published by |
| 10 |
* the Free Software Foundation; either version 2 of the License, or |
| 11 |
* (at your option) any later version. |
| 12 |
* |
| 13 |
* This program is distributed in the hope that it will be useful, |
| 14 |
* but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 15 |
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 16 |
* GNU General Public License for more details. |
| 17 |
* |
| 18 |
* You should have received a copy of the GNU General Public License |
| 19 |
* along with this program; if not, write to the Free Software |
| 20 |
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA |
| 21 |
*/ |
| 22 |
|
| 23 |
#include <sys/types.h> |
| 24 |
#include <sys/mman.h> |
| 25 |
#include <fcntl.h> |
| 26 |
#include <errno.h> |
| 27 |
#include <stdio.h> |
| 28 |
#include <stdlib.h> |
| 29 |
#include <string.h> |
| 30 |
#include <mach/vm_prot.h> |
| 31 |
#include <mach-o/loader.h> |
| 32 |
|
| 33 |
static const char progname[] = "lowmem"; |
| 34 |
|
| 35 |
/* |
| 36 |
* Under Mach there is very little assumed about the memory map of object |
| 37 |
* files. It is the job of the loader to create the initial memory map of an |
| 38 |
* executable. In a Mach-O executable there will be numerous loader commands |
| 39 |
* that the loader must process. Some of these will create the initial memory |
| 40 |
* map used by the executable. Under Darwin the static object file linker, |
| 41 |
* ld, automatically adds the __PAGEZERO segment to all executables. The |
| 42 |
* default size of this segment is the page size of the target system and |
| 43 |
* the initial and maximum permissions are set to allow no access. This is so |
| 44 |
* that all programs fault on a NULL pointer dereference. Arguably this is |
| 45 |
* incorrect and the maximum permissions shoould be rwx so that programs can |
| 46 |
* change this default behavior. Then programs could be written that assume |
| 47 |
* a null string at the null address, which was the convention on some |
| 48 |
* systems. In our case we need to have 8K mapped at zero for the low memory |
| 49 |
* globals and this program modifies the segment load command in the |
| 50 |
* basiliskII executable so that it can be used for data. |
| 51 |
*/ |
| 52 |
|
| 53 |
int |
| 54 |
main(int argc, const char *argv[]) |
| 55 |
{ |
| 56 |
int fd; |
| 57 |
char *addr; |
| 58 |
struct mach_header *machhead; |
| 59 |
struct segment_command *sc_cmd; |
| 60 |
|
| 61 |
if (argc != 2) { |
| 62 |
(void)fprintf(stderr, "Usage: %s executable\n", progname); |
| 63 |
exit(1); |
| 64 |
} |
| 65 |
|
| 66 |
fd = open(argv[1], O_RDWR, 0); |
| 67 |
if (fd == -1) { |
| 68 |
(void)fprintf(stderr, "%s: could not open %s: %s\n", |
| 69 |
progname, argv[1], strerror(errno)); |
| 70 |
exit(1); |
| 71 |
} |
| 72 |
|
| 73 |
/* |
| 74 |
* Size does not really matter, it will be rounded-up to a multiple |
| 75 |
* of the page size automatically. |
| 76 |
*/ |
| 77 |
addr = mmap(NULL, 0x1000, PROT_READ | PROT_WRITE, |
| 78 |
MAP_FILE | MAP_SHARED, fd, 0); |
| 79 |
if (addr == NULL) { |
| 80 |
(void)fprintf(stderr, "%s: could not mmap %s: %s\n", |
| 81 |
progname, argv[1], strerror(errno)); |
| 82 |
exit(1); |
| 83 |
} |
| 84 |
|
| 85 |
/* |
| 86 |
* Check to see if the Mach-O magic bytes are in the header. |
| 87 |
* If we cared about cross compiling we would also check against |
| 88 |
* MH_CIGAM and then change the endianness with every access, but |
| 89 |
* we do not care about that. |
| 90 |
*/ |
| 91 |
machhead = (void *)addr; |
| 92 |
if (machhead->magic != MH_MAGIC) { |
| 93 |
(void)fprintf(stderr, "%s: %s does not appear to be a Mach-O object file\n", |
| 94 |
progname, argv[1]); |
| 95 |
exit(1); |
| 96 |
} |
| 97 |
|
| 98 |
if (machhead->filetype != MH_EXECUTE) { |
| 99 |
(void)fprintf(stderr, "%s: %s does not appear to be an executable file\n", |
| 100 |
progname, argv[1]); |
| 101 |
exit(1); |
| 102 |
} |
| 103 |
|
| 104 |
if (machhead->ncmds == 0) { |
| 105 |
(void)fprintf(stderr, "%s: %s does not contain any load commands\n", |
| 106 |
progname, argv[1]); |
| 107 |
exit(1); |
| 108 |
} |
| 109 |
|
| 110 |
sc_cmd = (void *)&machhead[1]; |
| 111 |
if (sc_cmd->cmd != LC_SEGMENT){ |
| 112 |
(void)fprintf(stderr, "%s: load segment not first command in %s\n", |
| 113 |
progname, argv[1]); |
| 114 |
exit(1); |
| 115 |
} |
| 116 |
|
| 117 |
if (strncmp(sc_cmd->segname, "__PAGEZERO", |
| 118 |
sizeof (*sc_cmd->segname))) { |
| 119 |
(void)fprintf(stderr, "%s: zero page not first segment in %s\n", |
| 120 |
progname, argv[1]); |
| 121 |
exit(1); |
| 122 |
} |
| 123 |
|
| 124 |
/* change the permissions */ |
| 125 |
sc_cmd->maxprot = VM_PROT_ALL; |
| 126 |
sc_cmd->initprot = VM_PROT_ALL; |
| 127 |
|
| 128 |
/* |
| 129 |
* We do not make __PAGEZERO 8K in this program because then |
| 130 |
* all of the offsets would be wrong in the object file after |
| 131 |
* this segment. Instead we use the -pagezero_size option |
| 132 |
* to link the executable. |
| 133 |
*/ |
| 134 |
if (msync(addr, 0x1000, MS_SYNC) == -1) { |
| 135 |
(void)fprintf(stderr, "%s: could not sync %s: %s\n", |
| 136 |
progname, argv[1], strerror(errno)); |
| 137 |
exit(1); |
| 138 |
} |
| 139 |
|
| 140 |
if (munmap(addr, 0x1000) == -1) { |
| 141 |
(void)fprintf(stderr, "%s: could not unmap %s: %s\n", |
| 142 |
progname, argv[1], strerror(errno)); |
| 143 |
exit(1); |
| 144 |
} |
| 145 |
|
| 146 |
(void)close(fd); |
| 147 |
|
| 148 |
exit(0); |
| 149 |
} |
