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/* |
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* lowmem.c - enable access to low memory globals on Darwin |
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* |
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* Copyright (c) 2003 Michael Z. Sliczniak |
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* |
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* Basilisk II (C) 1997-2005 Christian Bauer |
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* |
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* This program is free software; you can redistribute it and/or modify |
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* it under the terms of the GNU General Public License as published by |
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* the Free Software Foundation; either version 2 of the License, or |
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* (at your option) any later version. |
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* |
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* This program is distributed in the hope that it will be useful, |
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* but WITHOUT ANY WARRANTY; without even the implied warranty of |
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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* GNU General Public License for more details. |
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* |
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* You should have received a copy of the GNU General Public License |
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* along with this program; if not, write to the Free Software |
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA |
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*/ |
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|
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#include <sys/types.h> |
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#include <sys/mman.h> |
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#include <fcntl.h> |
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#include <errno.h> |
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#include <stdio.h> |
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#include <string.h> |
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#include <mach/vm_prot.h> |
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#include <mach-o/loader.h> |
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|
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static const char progname[] = "lowmem"; |
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|
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/* |
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* Under Mach there is very little assumed about the memory map of object |
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* files. It is the job of the loader to create the initial memory map of an |
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* executable. In a Mach-O executable there will be numerous loader commands |
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* that the loader must process. Some of these will create the initial memory |
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* map used by the executable. Under Darwin the static object file linker, |
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* ld, automatically adds the __PAGEZERO segment to all executables. The |
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* default size of this segment is the page size of the target system and |
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* the initial and maximum permissions are set to allow no access. This is so |
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* that all programs fault on a NULL pointer dereference. Arguably this is |
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* incorrect and the maximum permissions shoould be rwx so that programs can |
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* change this default behavior. Then programs could be written that assume |
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* a null string at the null address, which was the convention on some |
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* systems. In our case we need to have 8K mapped at zero for the low memory |
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* globals and this program modifies the segment load command in the |
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* basiliskII executable so that it can be used for data. |
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*/ |
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|
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int |
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main(int argc, const char *argv[]) |
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{ |
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int fd; |
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char *addr; |
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struct mach_header *machhead; |
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struct segment_command *sc_cmd; |
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|
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if (argc != 2) { |
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(void)fprintf(stderr, "Usage: %s executable\n", progname); |
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exit(1); |
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} |
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|
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fd = open(argv[1], O_RDWR, 0); |
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if (fd == -1) { |
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(void)fprintf(stderr, "%s: could not open %s: %s\n", |
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progname, argv[1], strerror(errno)); |
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exit(1); |
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} |
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|
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/* |
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* Size does not really matter, it will be rounded-up to a multiple |
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* of the page size automatically. |
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*/ |
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addr = mmap(NULL, 0x1000, PROT_READ | PROT_WRITE, |
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MAP_FILE | MAP_SHARED, fd, 0); |
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if (addr == NULL) { |
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(void)fprintf(stderr, "%s: could not mmap %s: %s\n", |
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progname, argv[1], strerror(errno)); |
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exit(1); |
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} |
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|
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/* |
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* Check to see if the Mach-O magic bytes are in the header. |
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* If we cared about cross compiling we would also check against |
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* MH_CIGAM and then change the endianness with every access, but |
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* we do not care about that. |
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*/ |
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machhead = (void *)addr; |
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if (machhead->magic != MH_MAGIC) { |
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(void)fprintf(stderr, "%s: %s does not appear to be a Mach-O object file\n", |
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progname, argv[1]); |
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exit(1); |
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} |
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|
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if (machhead->filetype != MH_EXECUTE) { |
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(void)fprintf(stderr, "%s: %s does not appear to be an executable file\n", |
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progname, argv[1]); |
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exit(1); |
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} |
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|
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if (machhead->ncmds == 0) { |
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(void)fprintf(stderr, "%s: %s does not contain any load commands\n", |
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progname, argv[1]); |
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exit(1); |
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} |
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|
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sc_cmd = (void *)&machhead[1]; |
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if (sc_cmd->cmd != LC_SEGMENT){ |
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(void)fprintf(stderr, "%s: load segment not first command in %s\n", |
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progname, argv[1]); |
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exit(1); |
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} |
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|
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if (strncmp(sc_cmd->segname, "__PAGEZERO", |
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sizeof (*sc_cmd->segname))) { |
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(void)fprintf(stderr, "%s: zero page not first segment in %s\n", |
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progname, argv[1]); |
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exit(1); |
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} |
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|
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/* change the permissions */ |
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sc_cmd->maxprot = VM_PROT_ALL; |
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sc_cmd->initprot = VM_PROT_ALL; |
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|
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/* |
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* We do not make __PAGEZERO 8K in this program because then |
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* all of the offsets would be wrong in the object file after |
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* this segment. Instead we use the -pagezero_size option |
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* to link the executable. |
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*/ |
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if (msync(addr, 0x1000, MS_SYNC) == -1) { |
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(void)fprintf(stderr, "%s: could not sync %s: %s\n", |
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progname, argv[1], strerror(errno)); |
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exit(1); |
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} |
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|
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if (munmap(addr, 0x1000) == -1) { |
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(void)fprintf(stderr, "%s: could not unmap %s: %s\n", |
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progname, argv[1], strerror(errno)); |
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exit(1); |
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} |
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|
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(void)close(fd); |
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|
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exit(0); |
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} |
