Unix/Darwin/lowmem.c

/*
 *  lowmem.c - enable access to low memory globals on Darwin
 *
 *  Copyright (c) 2003 Michael Z. Sliczniak
 *
 *  Basilisk II (C) 1997-2005 Christian Bauer
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include <sys/types.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <mach/vm_prot.h>
#include <mach-o/loader.h>
#include <mach-o/fat.h>
#include <sys/stat.h>

static const char progname[] = "lowmem";
static const char *filename;

static int do_swap = 0;

static uint32_t target_uint32(uint32_t value)
{
        if (do_swap)
                value = OSSwapInt32(value);
        return value;
}

void pagezero_32(struct mach_header *machhead)
{
        struct segment_command *sc_cmd;

        if (target_uint32(machhead->filetype) != MH_EXECUTE) {
                (void)fprintf(stderr, "%s: %s does not appear to be an executable file\n",
                                progname, filename);
                exit(1);
        }
        if (machhead->ncmds == 0) {
                (void)fprintf(stderr, "%s: %s does not contain any load commands\n",
                                progname, filename);
                exit(1);
        }
        sc_cmd = (void *)&machhead[1];
        if (target_uint32(sc_cmd->cmd) != LC_SEGMENT){
                (void)fprintf(stderr, "%s: load segment not first command in %s\n",
                                progname, filename);
                exit(1);
        }
        if (strncmp(sc_cmd->segname, "__PAGEZERO", sizeof (*sc_cmd->segname))) {
                (void)fprintf(stderr, "%s: zero page not first segment in %s\n",
                                progname, filename);
                exit(1);
        }
        /* change the permissions */
        sc_cmd->maxprot = target_uint32(VM_PROT_ALL);
        sc_cmd->initprot = target_uint32(VM_PROT_ALL);
}

#if defined(MH_MAGIC_64)
void pagezero_64(struct mach_header_64 *machhead)
{
        struct segment_command_64 *sc_cmd;

        if (target_uint32(machhead->filetype) != MH_EXECUTE) {
                (void)fprintf(stderr, "%s: %s does not appear to be an executable file\n",
                                progname, filename);
                exit(1);
        }
        if (machhead->ncmds == 0) {
                (void)fprintf(stderr, "%s: %s does not contain any load commands\n",
                                progname, filename);
                exit(1);
        }
        sc_cmd = (void *)&machhead[1];
        if (target_uint32(sc_cmd->cmd) != LC_SEGMENT_64) {
                (void)fprintf(stderr, "%s: load segment not first command in %s\n",
                                progname, filename);
                exit(1);
        }
        if (strncmp(sc_cmd->segname, "__PAGEZERO", sizeof(*sc_cmd->segname))) {
                (void)fprintf(stderr, "%s: zero page not first segment in %s\n",
                                progname, filename);
                exit(1);
        }
        /* change the permissions */
        sc_cmd->maxprot = target_uint32(VM_PROT_ALL);
        sc_cmd->initprot = target_uint32(VM_PROT_ALL);
}
#endif

/*
 * Under Mach there is very little assumed about the memory map of object
 * files. It is the job of the loader to create the initial memory map of an
 * executable. In a Mach-O executable there will be numerous loader commands
 * that the loader must process. Some of these will create the initial memory
 * map used by the executable. Under Darwin the static object file linker,
 * ld, automatically adds the __PAGEZERO segment to all executables. The
 * default size of this segment is the page size of the target system and
 * the initial and maximum permissions are set to allow no access. This is so
 * that all programs fault on a NULL pointer dereference. Arguably this is
 * incorrect and the maximum permissions shoould be rwx so that programs can
 * change this default behavior. Then programs could be written that assume
 * a null string at the null address, which was the convention on some
 * systems. In our case we need to have 8K mapped at zero for the low memory
 * globals and this program modifies the segment load command in the
 * basiliskII executable so that it can be used for data.
 */

int
main(int argc, const char *argv[])
{
        int fd;
        char *addr;
        off_t file_size;
        struct mach_header *machhead;
#if defined(MH_MAGIC_64)
        struct mach_header_64 *machhead64;
#endif
        struct fat_header *fathead;
        struct stat f;

        if (argc != 2) {
                (void)fprintf(stderr, "Usage: %s executable\n", progname);
                exit(1);
        }

        filename = argv[1];

        if (stat(filename, &f)) {
                (void)fprintf(stderr, "%s: could not stat %s: %s\n",
                        progname, filename, strerror(errno));
                exit(1);
        }
        file_size = f.st_size;

        fd = open(filename, O_RDWR, 0);
        if (fd == -1) {
                (void)fprintf(stderr, "%s: could not open %s: %s\n",
                        progname, filename, strerror(errno));
                exit(1);
        }

        /*
         * Size does not really matter, it will be rounded-up to a multiple
         * of the page size automatically.
         */
        addr = mmap(NULL, file_size, PROT_READ | PROT_WRITE,
            MAP_FILE | MAP_SHARED, fd, 0);
        if (addr == NULL || addr == MAP_FAILED) {
                (void)fprintf(stderr, "%s: could not mmap %s: %s\n",
                                progname, filename, strerror(errno));
                exit(1);
        }

        /*
         * Check to see if the Mach-O magic bytes are in the header.
         */
        machhead = (void *)addr;
#if defined(MH_MAGIC_64)
        machhead64 = (void *)addr;
#endif
        fathead = (void *)addr;

#if defined(MH_MAGIC_64)
        do_swap = machhead->magic == MH_CIGAM || fathead->magic == FAT_CIGAM || machhead64->magic == MH_CIGAM_64;
#else
        do_swap = machhead->magic == MH_CIGAM || fathead->magic == FAT_CIGAM;
#endif

        if (target_uint32(machhead->magic) == MH_MAGIC) {
                pagezero_32(machhead);
#if defined(MH_MAGIC_64)
        } else if (target_uint32(machhead64->magic) == MH_MAGIC_64) {
                pagezero_64(machhead64);
#endif
        } else if (target_uint32(fathead->magic) == FAT_MAGIC) {
                struct fat_arch *arch = (void *)&fathead[1];
                int saved_swap = do_swap;
                int i;
                for (i = 0; i < target_uint32(fathead->nfat_arch); ++i, ++arch) {
                        machhead   = (void *)(addr + target_uint32(arch->offset));
#if defined(MH_MAGIC_64)
                        machhead64 = (void *)(addr + target_uint32(arch->offset));
#endif
#if defined(MH_MAGIC_64)
                        do_swap = machhead->magic == MH_CIGAM || machhead64->magic == MH_CIGAM_64;
#else
                        do_swap = machhead->magic == MH_CIGAM;
#endif
                        if (target_uint32(machhead->magic) == MH_MAGIC) {
                                pagezero_32(machhead);
#if defined(MH_MAGIC_64)
                        } else if (target_uint32(machhead64->magic) == MH_MAGIC_64) {
                                pagezero_64(machhead64);
#endif
                        } else {
                                (void)fprintf(stderr, "%s: %s does not appear to be a Mach-O object file\n",
                                                progname, filename);
                                exit(1);
                        }
                        do_swap = saved_swap;
                }
        } else {
                (void)fprintf(stderr, "%s: %s does not appear to be a Mach-O object file\n",
                                progname, filename);
                exit(1);
        }

        /*
         * We do not make __PAGEZERO 8K in this program because then
         * all of the offsets would be wrong in the object file after
         * this segment. Instead we use the -pagezero_size option
         * to link the executable.
         */
        if (msync(addr, file_size, MS_SYNC) == -1) {
                (void)fprintf(stderr, "%s: could not sync %s: %s\n",
                                progname, filename, strerror(errno));
                exit(1);
        }

        if (munmap(addr, file_size) == -1) {
                (void)fprintf(stderr, "%s: could not unmap %s: %s\n",
                                progname, filename, strerror(errno));
                exit(1);
        }

        (void)close(fd);

        exit(0);
}
Revision:	1.9
Committed:	2011-12-27T21:01:32Z (12 years, 11 months ago) by asvitkine
Content type:	text/plain
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.8:	+9 -11 lines
Log Message:	get file size using stat, which seems to be more reliable
#	User	Rev	Content
1	gbeauche	1.1	/*
2			* lowmem.c - enable access to low memory globals on Darwin
3			*
4			* Copyright (c) 2003 Michael Z. Sliczniak
5			*
6	gbeauche	1.3	* Basilisk II (C) 1997-2005 Christian Bauer
7	gbeauche	1.1	*
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	asvitkine	1.4	#include <stdlib.h>
29	gbeauche	1.1	#include <string.h>
30			#include <mach/vm_prot.h>
31			#include <mach-o/loader.h>
32	asvitkine	1.6	#include <mach-o/fat.h>
33	asvitkine	1.9	#include <sys/stat.h>
34	gbeauche	1.1
35			static const char progname[] = "lowmem";
36	asvitkine	1.6	static const char *filename;
37	gbeauche	1.1
38	gbeauche	1.5	static int do_swap = 0;
39
40			static uint32_t target_uint32(uint32_t value)
41			{
42			if (do_swap)
43	asvitkine	1.6	value = OSSwapInt32(value);
44	gbeauche	1.5	return value;
45			}
46
47	asvitkine	1.6	void pagezero_32(struct mach_header *machhead)
48			{
49			struct segment_command *sc_cmd;
50
51			if (target_uint32(machhead->filetype) != MH_EXECUTE) {
52			(void)fprintf(stderr, "%s: %s does not appear to be an executable file\n",
53			progname, filename);
54			exit(1);
55			}
56			if (machhead->ncmds == 0) {
57			(void)fprintf(stderr, "%s: %s does not contain any load commands\n",
58			progname, filename);
59			exit(1);
60			}
61			sc_cmd = (void *)&machhead[1];
62			if (target_uint32(sc_cmd->cmd) != LC_SEGMENT){
63			(void)fprintf(stderr, "%s: load segment not first command in %s\n",
64			progname, filename);
65			exit(1);
66			}
67			if (strncmp(sc_cmd->segname, "__PAGEZERO", sizeof (*sc_cmd->segname))) {
68			(void)fprintf(stderr, "%s: zero page not first segment in %s\n",
69			progname, filename);
70			exit(1);
71			}
72			/* change the permissions */
73			sc_cmd->maxprot = target_uint32(VM_PROT_ALL);
74			sc_cmd->initprot = target_uint32(VM_PROT_ALL);
75			}
76
77			#if defined(MH_MAGIC_64)
78			void pagezero_64(struct mach_header_64 *machhead)
79			{
80			struct segment_command_64 *sc_cmd;
81
82			if (target_uint32(machhead->filetype) != MH_EXECUTE) {
83			(void)fprintf(stderr, "%s: %s does not appear to be an executable file\n",
84			progname, filename);
85			exit(1);
86			}
87			if (machhead->ncmds == 0) {
88			(void)fprintf(stderr, "%s: %s does not contain any load commands\n",
89			progname, filename);
90			exit(1);
91			}
92			sc_cmd = (void *)&machhead[1];
93			if (target_uint32(sc_cmd->cmd) != LC_SEGMENT_64) {
94			(void)fprintf(stderr, "%s: load segment not first command in %s\n",
95			progname, filename);
96			exit(1);
97			}
98			if (strncmp(sc_cmd->segname, "__PAGEZERO", sizeof(*sc_cmd->segname))) {
99			(void)fprintf(stderr, "%s: zero page not first segment in %s\n",
100			progname, filename);
101			exit(1);
102			}
103			/* change the permissions */
104			sc_cmd->maxprot = target_uint32(VM_PROT_ALL);
105			sc_cmd->initprot = target_uint32(VM_PROT_ALL);
106			}
107			#endif
108
109			/*
110	gbeauche	1.1	* Under Mach there is very little assumed about the memory map of object
111			* files. It is the job of the loader to create the initial memory map of an
112			* executable. In a Mach-O executable there will be numerous loader commands
113			* that the loader must process. Some of these will create the initial memory
114			* map used by the executable. Under Darwin the static object file linker,
115			* ld, automatically adds the __PAGEZERO segment to all executables. The
116			* default size of this segment is the page size of the target system and
117			* the initial and maximum permissions are set to allow no access. This is so
118			* that all programs fault on a NULL pointer dereference. Arguably this is
119			* incorrect and the maximum permissions shoould be rwx so that programs can
120			* change this default behavior. Then programs could be written that assume
121			* a null string at the null address, which was the convention on some
122			* systems. In our case we need to have 8K mapped at zero for the low memory
123			* globals and this program modifies the segment load command in the
124			* basiliskII executable so that it can be used for data.
125			*/
126
127			int
128			main(int argc, const char *argv[])
129			{
130			int fd;
131			char *addr;
132	asvitkine	1.6	off_t file_size;
133	gbeauche	1.1	struct mach_header *machhead;
134	asvitkine	1.6	#if defined(MH_MAGIC_64)
135			struct mach_header_64 *machhead64;
136			#endif
137			struct fat_header *fathead;
138	asvitkine	1.9	struct stat f;
139	gbeauche	1.1
140			if (argc != 2) {
141			(void)fprintf(stderr, "Usage: %s executable\n", progname);
142			exit(1);
143			}
144
145	asvitkine	1.6	filename = argv[1];
146
147	asvitkine	1.9	if (stat(filename, &f)) {
148			(void)fprintf(stderr, "%s: could not stat %s: %s\n",
149			progname, filename, strerror(errno));
150			exit(1);
151			}
152			file_size = f.st_size;
153
154	asvitkine	1.6	fd = open(filename, O_RDWR, 0);
155	gbeauche	1.1	if (fd == -1) {
156			(void)fprintf(stderr, "%s: could not open %s: %s\n",
157	asvitkine	1.6	progname, filename, strerror(errno));
158	gbeauche	1.1	exit(1);
159			}
160
161			/*
162			* Size does not really matter, it will be rounded-up to a multiple
163			* of the page size automatically.
164			*/
165	asvitkine	1.6	addr = mmap(NULL, file_size, PROT_READ \| PROT_WRITE,
166	gbeauche	1.1	MAP_FILE \| MAP_SHARED, fd, 0);
167	asvitkine	1.8	if (addr == NULL \|\| addr == MAP_FAILED) {
168	gbeauche	1.1	(void)fprintf(stderr, "%s: could not mmap %s: %s\n",
169	asvitkine	1.6	progname, filename, strerror(errno));
170	gbeauche	1.1	exit(1);
171			}
172
173			/*
174			* Check to see if the Mach-O magic bytes are in the header.
175			*/
176			machhead = (void *)addr;
177	asvitkine	1.6	#if defined(MH_MAGIC_64)
178			machhead64 = (void *)addr;
179			#endif
180			fathead = (void *)addr;
181
182			#if defined(MH_MAGIC_64)
183			do_swap = machhead->magic == MH_CIGAM \|\| fathead->magic == FAT_CIGAM \|\| machhead64->magic == MH_CIGAM_64;
184			#else
185			do_swap = machhead->magic == MH_CIGAM \|\| fathead->magic == FAT_CIGAM;
186			#endif
187
188			if (target_uint32(machhead->magic) == MH_MAGIC) {
189			pagezero_32(machhead);
190			#if defined(MH_MAGIC_64)
191			} else if (target_uint32(machhead64->magic) == MH_MAGIC_64) {
192			pagezero_64(machhead64);
193			#endif
194			} else if (target_uint32(fathead->magic) == FAT_MAGIC) {
195			struct fat_arch arch = (void )&fathead[1];
196			int saved_swap = do_swap;
197			int i;
198			for (i = 0; i < target_uint32(fathead->nfat_arch); ++i, ++arch) {
199			machhead = (void *)(addr + target_uint32(arch->offset));
200			#if defined(MH_MAGIC_64)
201			machhead64 = (void *)(addr + target_uint32(arch->offset));
202			#endif
203			#if defined(MH_MAGIC_64)
204			do_swap = machhead->magic == MH_CIGAM \|\| machhead64->magic == MH_CIGAM_64;
205			#else
206			do_swap = machhead->magic == MH_CIGAM;
207			#endif
208			if (target_uint32(machhead->magic) == MH_MAGIC) {
209			pagezero_32(machhead);
210			#if defined(MH_MAGIC_64)
211			} else if (target_uint32(machhead64->magic) == MH_MAGIC_64) {
212			pagezero_64(machhead64);
213			#endif
214			} else {
215			(void)fprintf(stderr, "%s: %s does not appear to be a Mach-O object file\n",
216			progname, filename);
217			exit(1);
218			}
219			do_swap = saved_swap;
220			}
221			} else {
222	gbeauche	1.1	(void)fprintf(stderr, "%s: %s does not appear to be a Mach-O object file\n",
223	asvitkine	1.6	progname, filename);
224	gbeauche	1.1	exit(1);
225			}
226
227			/*
228			* We do not make __PAGEZERO 8K in this program because then
229			* all of the offsets would be wrong in the object file after
230			* this segment. Instead we use the -pagezero_size option
231			* to link the executable.
232			*/
233	asvitkine	1.6	if (msync(addr, file_size, MS_SYNC) == -1) {
234	gbeauche	1.1	(void)fprintf(stderr, "%s: could not sync %s: %s\n",
235	asvitkine	1.6	progname, filename, strerror(errno));
236	gbeauche	1.1	exit(1);
237			}
238
239	asvitkine	1.6	if (munmap(addr, file_size) == -1) {
240	gbeauche	1.1	(void)fprintf(stderr, "%s: could not unmap %s: %s\n",
241	asvitkine	1.6	progname, filename, strerror(errno));
242	gbeauche	1.1	exit(1);
243			}
244
245			(void)close(fd);
246
247			exit(0);
248			}