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>

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;

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

        filename = argv[1];

        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);
        }

        file_size = lseek(fd, 0, SEEK_END);
        if (file_size == -1) {
                // for some mysterious reason, this sometimes fails...
                file_size = 0x1000;
#if 0
                (void)fprintf(stderr, "%s: could not get size of %s: %s\n",
                      progname, filename, strerror(errno));
                exit(1);
#endif
        }

        /*
         * 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) {
                (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:	1.7
Committed:	2011-12-27T19:50:38Z (12 years, 10 months ago) by asvitkine
Content type:	text/plain
Branch:	MAIN
Changes since 1.6:	+0 -1 lines
Log Message:	remove extra comment start
#	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	gbeauche	1.1
34			static const char progname[] = "lowmem";
35	asvitkine	1.6	static const char *filename;
36	gbeauche	1.1
37	gbeauche	1.5	static int do_swap = 0;
38
39			static uint32_t target_uint32(uint32_t value)
40			{
41			if (do_swap)
42	asvitkine	1.6	value = OSSwapInt32(value);
43	gbeauche	1.5	return value;
44			}
45
46	asvitkine	1.6	void pagezero_32(struct mach_header *machhead)
47			{
48			struct segment_command *sc_cmd;
49
50			if (target_uint32(machhead->filetype) != MH_EXECUTE) {
51			(void)fprintf(stderr, "%s: %s does not appear to be an executable file\n",
52			progname, filename);
53			exit(1);
54			}
55			if (machhead->ncmds == 0) {
56			(void)fprintf(stderr, "%s: %s does not contain any load commands\n",
57			progname, filename);
58			exit(1);
59			}
60			sc_cmd = (void *)&machhead[1];
61			if (target_uint32(sc_cmd->cmd) != LC_SEGMENT){
62			(void)fprintf(stderr, "%s: load segment not first command in %s\n",
63			progname, filename);
64			exit(1);
65			}
66			if (strncmp(sc_cmd->segname, "__PAGEZERO", sizeof (*sc_cmd->segname))) {
67			(void)fprintf(stderr, "%s: zero page not first segment in %s\n",
68			progname, filename);
69			exit(1);
70			}
71			/* change the permissions */
72			sc_cmd->maxprot = target_uint32(VM_PROT_ALL);
73			sc_cmd->initprot = target_uint32(VM_PROT_ALL);
74			}
75
76			#if defined(MH_MAGIC_64)
77			void pagezero_64(struct mach_header_64 *machhead)
78			{
79			struct segment_command_64 *sc_cmd;
80
81			if (target_uint32(machhead->filetype) != MH_EXECUTE) {
82			(void)fprintf(stderr, "%s: %s does not appear to be an executable file\n",
83			progname, filename);
84			exit(1);
85			}
86			if (machhead->ncmds == 0) {
87			(void)fprintf(stderr, "%s: %s does not contain any load commands\n",
88			progname, filename);
89			exit(1);
90			}
91			sc_cmd = (void *)&machhead[1];
92			if (target_uint32(sc_cmd->cmd) != LC_SEGMENT_64) {
93			(void)fprintf(stderr, "%s: load segment not first command in %s\n",
94			progname, filename);
95			exit(1);
96			}
97			if (strncmp(sc_cmd->segname, "__PAGEZERO", sizeof(*sc_cmd->segname))) {
98			(void)fprintf(stderr, "%s: zero page not first segment in %s\n",
99			progname, filename);
100			exit(1);
101			}
102			/* change the permissions */
103			sc_cmd->maxprot = target_uint32(VM_PROT_ALL);
104			sc_cmd->initprot = target_uint32(VM_PROT_ALL);
105			}
106			#endif
107
108			/*
109	gbeauche	1.1	* Under Mach there is very little assumed about the memory map of object
110			* files. It is the job of the loader to create the initial memory map of an
111			* executable. In a Mach-O executable there will be numerous loader commands
112			* that the loader must process. Some of these will create the initial memory
113			* map used by the executable. Under Darwin the static object file linker,
114			* ld, automatically adds the __PAGEZERO segment to all executables. The
115			* default size of this segment is the page size of the target system and
116			* the initial and maximum permissions are set to allow no access. This is so
117			* that all programs fault on a NULL pointer dereference. Arguably this is
118			* incorrect and the maximum permissions shoould be rwx so that programs can
119			* change this default behavior. Then programs could be written that assume
120			* a null string at the null address, which was the convention on some
121			* systems. In our case we need to have 8K mapped at zero for the low memory
122			* globals and this program modifies the segment load command in the
123			* basiliskII executable so that it can be used for data.
124			*/
125
126			int
127			main(int argc, const char *argv[])
128			{
129			int fd;
130			char *addr;
131	asvitkine	1.6	off_t file_size;
132	gbeauche	1.1	struct mach_header *machhead;
133	asvitkine	1.6	#if defined(MH_MAGIC_64)
134			struct mach_header_64 *machhead64;
135			#endif
136			struct fat_header *fathead;
137	gbeauche	1.1
138			if (argc != 2) {
139			(void)fprintf(stderr, "Usage: %s executable\n", progname);
140			exit(1);
141			}
142
143	asvitkine	1.6	filename = argv[1];
144
145			fd = open(filename, O_RDWR, 0);
146	gbeauche	1.1	if (fd == -1) {
147			(void)fprintf(stderr, "%s: could not open %s: %s\n",
148	asvitkine	1.6	progname, filename, strerror(errno));
149	gbeauche	1.1	exit(1);
150			}
151
152	asvitkine	1.6	file_size = lseek(fd, 0, SEEK_END);
153			if (file_size == -1) {
154			// for some mysterious reason, this sometimes fails...
155			file_size = 0x1000;
156			#if 0
157			(void)fprintf(stderr, "%s: could not get size of %s: %s\n",
158			progname, filename, strerror(errno));
159			exit(1);
160			#endif
161			}
162
163	gbeauche	1.1	/*
164			* Size does not really matter, it will be rounded-up to a multiple
165			* of the page size automatically.
166			*/
167	asvitkine	1.6	addr = mmap(NULL, file_size, PROT_READ \| PROT_WRITE,
168	gbeauche	1.1	MAP_FILE \| MAP_SHARED, fd, 0);
169			if (addr == NULL) {
170			(void)fprintf(stderr, "%s: could not mmap %s: %s\n",
171	asvitkine	1.6	progname, filename, strerror(errno));
172	gbeauche	1.1	exit(1);
173			}
174
175			/*
176			* Check to see if the Mach-O magic bytes are in the header.
177			*/
178			machhead = (void *)addr;
179	asvitkine	1.6	#if defined(MH_MAGIC_64)
180			machhead64 = (void *)addr;
181			#endif
182			fathead = (void *)addr;
183
184			#if defined(MH_MAGIC_64)
185			do_swap = machhead->magic == MH_CIGAM \|\| fathead->magic == FAT_CIGAM \|\| machhead64->magic == MH_CIGAM_64;
186			#else
187			do_swap = machhead->magic == MH_CIGAM \|\| fathead->magic == FAT_CIGAM;
188			#endif
189
190			if (target_uint32(machhead->magic) == MH_MAGIC) {
191			pagezero_32(machhead);
192			#if defined(MH_MAGIC_64)
193			} else if (target_uint32(machhead64->magic) == MH_MAGIC_64) {
194			pagezero_64(machhead64);
195			#endif
196			} else if (target_uint32(fathead->magic) == FAT_MAGIC) {
197			struct fat_arch arch = (void )&fathead[1];
198			int saved_swap = do_swap;
199			int i;
200			for (i = 0; i < target_uint32(fathead->nfat_arch); ++i, ++arch) {
201			machhead = (void *)(addr + target_uint32(arch->offset));
202			#if defined(MH_MAGIC_64)
203			machhead64 = (void *)(addr + target_uint32(arch->offset));
204			#endif
205			#if defined(MH_MAGIC_64)
206			do_swap = machhead->magic == MH_CIGAM \|\| machhead64->magic == MH_CIGAM_64;
207			#else
208			do_swap = machhead->magic == MH_CIGAM;
209			#endif
210			if (target_uint32(machhead->magic) == MH_MAGIC) {
211			pagezero_32(machhead);
212			#if defined(MH_MAGIC_64)
213			} else if (target_uint32(machhead64->magic) == MH_MAGIC_64) {
214			pagezero_64(machhead64);
215			#endif
216			} else {
217			(void)fprintf(stderr, "%s: %s does not appear to be a Mach-O object file\n",
218			progname, filename);
219			exit(1);
220			}
221			do_swap = saved_swap;
222			}
223			} else {
224	gbeauche	1.1	(void)fprintf(stderr, "%s: %s does not appear to be a Mach-O object file\n",
225	asvitkine	1.6	progname, filename);
226	gbeauche	1.1	exit(1);
227			}
228
229			/*
230			* We do not make __PAGEZERO 8K in this program because then
231			* all of the offsets would be wrong in the object file after
232			* this segment. Instead we use the -pagezero_size option
233			* to link the executable.
234			*/
235	asvitkine	1.6	if (msync(addr, file_size, MS_SYNC) == -1) {
236	gbeauche	1.1	(void)fprintf(stderr, "%s: could not sync %s: %s\n",
237	asvitkine	1.6	progname, filename, strerror(errno));
238	gbeauche	1.1	exit(1);
239			}
240
241	asvitkine	1.6	if (munmap(addr, file_size) == -1) {
242	gbeauche	1.1	(void)fprintf(stderr, "%s: could not unmap %s: %s\n",
243	asvitkine	1.6	progname, filename, strerror(errno));
244	gbeauche	1.1	exit(1);
245			}
246
247			(void)close(fd);
248
249			exit(0);
250			}