Mach-O学习

/*
 * The 32-bit mach header appears at the very beginning of the object file for
 * 32-bit architectures.
 */
struct mach_header {
	uint32_t	magic;		/* mach magic number identifier */
	cpu_type_t	cputype;	/* cpu specifier */
	cpu_subtype_t	cpusubtype;	/* machine specifier */
	uint32_t	filetype;	/* type of file */
	uint32_t	ncmds;		/* number of load commands */
	uint32_t	sizeofcmds;	/* the size of all the load commands */
	uint32_t	flags;		/* flags */
};
/* Constant for the magic field of the mach_header (32-bit architectures) */
#define	MH_MAGIC	0xfeedface	/* the mach magic number */
#define MH_CIGAM	0xcefaedfe	/* NXSwapInt(MH_MAGIC) */
/*
 * The 64-bit mach header appears at the very beginning of object files for
 * 64-bit architectures.
 */
struct mach_header_64 {
	uint32_t	magic;		/* mach magic number identifier */
	cpu_type_t	cputype;	/* cpu specifier */
	cpu_subtype_t	cpusubtype;	/* machine specifier */
	uint32_t	filetype;	/* type of file */
	uint32_t	ncmds;		/* number of load commands */
	uint32_t	sizeofcmds;	/* the size of all the load commands */
	uint32_t	flags;		/* flags */
	uint32_t	reserved;	/* reserved */
};
/* Constant for the magic field of the mach_header_64 (64-bit architectures) */
#define MH_MAGIC_64 0xfeedfacf /* the 64-bit mach magic number */
#define MH_CIGAM_64 0xcffaedfe /* NXSwapInt(MH_MAGIC_64) */

struct load_command {
    uint32_t cmd;        /* type of load command */
    uint32_t cmdsize;    /* total size of command in bytes */
};

struct symtab_command {
    uint32_t    cmd;        /* LC_SYMTAB */
    uint32_t    cmdsize;    /* sizeof(struct symtab_command) */
    uint32_t    symoff;        /* symbol table offset */
    uint32_t    nsyms;        /* number of symbol table entries */
    uint32_t    stroff;        /* string table offset */
    uint32_t    strsize;    /* string table size in bytes */
};

struct segment_command { /* for 32-bit architectures */
	uint32_t	cmd;		/* LC_SEGMENT */
	uint32_t	cmdsize;	/* includes sizeof section structs */
	char		segname[16];	/* segment name */
	uint32_t	vmaddr;		/* memory address of this segment 段的虚拟内存地址*/
	uint32_t	vmsize;		/* memory size of this segment  段的虚拟内存大小*/
	uint32_t	fileoff;	/* file offset of this segment  段在文件中的偏移量*/
	uint32_t	filesize;	/* amount to map from the file  段在文件中的大小*/
	vm_prot_t	maxprot;	/* maximum VM protection */
	vm_prot_t	initprot;	/* initial VM protection */
	uint32_t	nsects;		/* number of sections in segment */
	uint32_t	flags;		/* flags */
};
struct segment_command_64 { /* for 64-bit architectures */
	uint32_t	cmd;		/* LC_SEGMENT_64 */
	uint32_t	cmdsize;	/* includes sizeof section_64 structs */
	char		segname[16];	/* segment name */
	uint64_t	vmaddr;		/* memory address of this segment */
	uint64_t	vmsize;		/* memory size of this segment */
	uint64_t	fileoff;	/* file offset of this segment */
	uint64_t	filesize;	/* amount to map from the file */
	vm_prot_t	maxprot;	/* maximum VM protection */
	vm_prot_t	initprot;	/* initial VM protection */
	uint32_t	nsects;		/* number of sections in segment */
	uint32_t	flags;		/* flags */
};

struct section { /* for 32-bit architectures */
	char		sectname[16];	/* name of this section */
	char		segname[16];	/* segment this section goes in */
	uint32_t	addr;		/* memory address of this section 该节在内存中的起始位置*/
	uint32_t	size;		/* size in bytes of this section 该节的大小*/
	uint32_t	offset;		/* file offset of this section 该节的文件偏移*/
	uint32_t	align;		/* section alignment (power of 2) 字节大小对齐*/
	uint32_t	reloff;		/* file offset of relocation entries 重定位入口的文件偏移*/
	uint32_t	nreloc;		/* number of relocation entries 需要重定位的入口数量*/
	uint32_t	flags;		/* flags (section type and attributes) */
	uint32_t	reserved1;	/* reserved (for offset or index) */
	uint32_t	reserved2;	/* reserved (for count or sizeof) */
};
struct section_64 { /* for 64-bit architectures */
	char		sectname[16];	/* name of this section */
	char		segname[16];	/* segment this section goes in */
	uint64_t	addr;		/* memory address of this section */
	uint64_t	size;		/* size in bytes of this section */
	uint32_t	offset;		/* file offset of this section */
	uint32_t	align;		/* section alignment (power of 2) */
	uint32_t	reloff;		/* file offset of relocation entries */
	uint32_t	nreloc;		/* number of relocation entries */
	uint32_t	flags;		/* flags (section type and attributes)*/
	uint32_t	reserved1;	/* reserved (for offset or index) */
	uint32_t	reserved2;	/* reserved (for count or sizeof) */
	uint32_t	reserved3;	/* reserved */
};

% mkdir ~/Desktop/objcio-command-line
% cd !$
% touch helloworld.c

% open -e helloworld.c

#include <stdio.h>
int main(int argc, char *argv[])
{
    printf("Hello World!\n");
    return 0;
}

% xcrun clang helloworld.c
% ./a.out

% xcrun size -x -l -m a.out

Segment __PAGEZERO: 0x100000000 (vmaddr 0x0 fileoff 0)
Segment __TEXT: 0x1000 (vmaddr 0x100000000 fileoff 0)
    Section __text: 0x37 (addr 0x100000f30 offset 3888)
    Section __stubs: 0x6 (addr 0x100000f68 offset 3944)
    Section __stub_helper: 0x1a (addr 0x100000f70 offset 3952)
    Section __cstring: 0xe (addr 0x100000f8a offset 3978)
    Section __unwind_info: 0x48 (addr 0x100000f98 offset 3992)
    Section __eh_frame: 0x18 (addr 0x100000fe0 offset 4064)
    total 0xc5
Segment __DATA: 0x1000 (vmaddr 0x100001000 fileoff 4096)
    Section __nl_symbol_ptr: 0x10 (addr 0x100001000 offset 4096)
    Section __la_symbol_ptr: 0x8 (addr 0x100001010 offset 4112)
    total 0x18
Segment __LINKEDIT: 0x1000 (vmaddr 0x100002000 fileoff 8192)
total 0x100003000

% xcrun otool -s __TEXT __text a.out
a.out:
(__TEXT,__text) section
0000000100000f30 55 48 89 e5 48 83 ec 20 48 8d 05 4b 00 00 00 c7
0000000100000f40 45 fc 00 00 00 00 89 7d f8 48 89 75 f0 48 89 c7
0000000100000f50 b0 00 e8 11 00 00 00 b9 00 00 00 00 89 45 ec 89
0000000100000f60 c8 48 83 c4 20 5d c3

% xcrun otool -v -t a.out
a.out:
(__TEXT,__text) section
_main:
0000000100000f30    pushq   %rbp
0000000100000f31    movq    %rsp, %rbp
0000000100000f34    subq    $0x20, %rsp
0000000100000f38    leaq    0x4b(%rip), %rax
0000000100000f3f    movl    $0x0, 0xfffffffffffffffc(%rbp)
0000000100000f46    movl    %edi, 0xfffffffffffffff8(%rbp)
0000000100000f49    movq    %rsi, 0xfffffffffffffff0(%rbp)
0000000100000f4d    movq    %rax, %rdi
0000000100000f50    movb    $0x0, %al
0000000100000f52    callq   0x100000f68
0000000100000f57    movl    $0x0, %ecx
0000000100000f5c    movl    %eax, 0xffffffffffffffec(%rbp)
0000000100000f5f    movl    %ecx, %eax
0000000100000f61    addq    $0x20, %rsp
0000000100000f65    popq    %rbp
0000000100000f66    ret

% xcrun otool -v -s __TEXT __cstring a.out
a.out:
Contents of (__TEXT,__cstring) section

0x0000000100000f8a  Hello World!\n

% xcrun otool -v -s __TEXT __eh_frame a.out
a.out:
Contents of (__TEXT,__eh_frame) section
0000000100000fe0    14 00 00 00 00 00 00 00 01 7a 52 00 01 78 10 01
0000000100000ff0    10 0c 07 08 90 01 00 00

#include <mach-o/dyld.h>
#include <mach/mach.h>
static uintptr_t imageLoadAddrStart = 0;        //app可执行文件的加载起始地址
static uintptr_t imageLoadAddrEnd = 0;          //app可执行文件的加载结束地址

void resetImageLoadAddress(void) {
	NSString *executableName = [[[NSBundle mainBundle] infoDictionary] objectForKey:@"CFBundleExecutable"];//可执行文件名

	for(int i = 0; i < _dyld_image_count(); i++) {
		const struct mach_header* header = _dyld_get_image_header(i);
		const char *name = _dyld_get_image_name(i);
		if(name == NULL) {
			continue;
		}

		NSString *imageName = [[NSString stringWithUTF8String:name] lastPathComponent];
		if(imageName == nil || [imageName isEqualToString:executableName] == NO) {
			continue;
		}

		uintptr_t cmdPtr = 0;
		if(header->magic == MH_MAGIC || header->magic == MH_CIGAM) {
			cmdPtr = (uintptr_t)(header + 1);
		}else if(header->magic == MH_MAGIC_64 || header->magic == MH_CIGAM_64) {
			cmdPtr = (uintptr_t)(((struct mach_header_64 *)header) + 1);
		}else {
			continue;
		}
		//实际是从_TEXT段开始的，而不是SEG_PAGEZERO（待验证）
		for(uint32_t iCmd = 0; iCmd < header->ncmds; iCmd++) {
			struct load_command* loadCmd = (struct load_command*)cmdPtr;
			cmdPtr += loadCmd->cmdsize;
			if(loadCmd->cmd == LC_SEGMENT) {
				struct segment_command *segPtr = (struct segment_command *)cmdPtr;
				if(strcmp(segPtr->segname, SEG_TEXT) == 0) {
					imageLoadAddrStart = (uintptr_t)(segPtr->vmaddr);
					imageLoadAddrEnd = (uintptr_t)(segPtr->vmaddr + segPtr->vmsize);
				}else if(strcmp(segPtr->segname, SEG_PAGEZERO) == 0){

				}else if(strcmp(segPtr->segname, SEG_DATA) == 0){
					imageLoadAddrEnd += (uintptr_t)(segPtr->vmsize);
				}
				NSLog(@"%d、 %s vmaddr:0x%08x vmsize:0x%08x", iCmd, segPtr->segname, segPtr->vmaddr, segPtr->vmsize);
			}else if(loadCmd->cmd == LC_SEGMENT_64) {
				struct segment_command_64 *segPtr = (struct segment_command_64 *)cmdPtr;
				if(strcmp(segPtr->segname, SEG_TEXT) == 0) {
					imageLoadAddrStart = (uintptr_t)(segPtr->vmaddr);
					imageLoadAddrEnd = (uintptr_t)(segPtr->vmaddr + segPtr->vmsize);
				}else if(strcmp(segPtr->segname, SEG_PAGEZERO) == 0){

				}else if(strcmp(segPtr->segname, SEG_DATA) == 0){
					imageLoadAddrEnd += (uintptr_t)(segPtr->vmsize);
				}
				NSLog(@"%d、 %s vmaddr:0x%llx vmsize:0x%llx", iCmd, segPtr->segname, segPtr->vmaddr, segPtr->vmsize);
			}
		}
		imageLoadAddrEnd = (uintptr_t)header + (imageLoadAddrEnd - imageLoadAddrStart);
		imageLoadAddrStart = (uintptr_t)header;
		NSLog(@"%@ load addr: 0x%lx ~0x%lx", executableName, (uintptr_t)imageLoadAddrStart, (uintptr_t)imageLoadAddrEnd);
		break;
	}

	assert(imageLoadAddrStart && imageLoadAddrEnd);
}