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mach-o.c
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mach-o.c
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#include "mach-o.h"
#include "../compiler.h"
#include "../log.h"
#include "../util.h"
#include <mach-o/arm64/reloc.h>
#include <mach-o/loader.h>
#include <mach-o/reloc.h>
#include <mach/machine.h>
#include <stdint.h>
#include <stdio.h>
void write_mach_header(FILE *file, const struct compile_args *args) {
struct mach_header_64 header;
memset(&header, 0, sizeof(header));
header.magic = MH_MAGIC_64;
switch (args->target_arch) {
case COMPILE_TARGET_ARCH_NATIVE:
bug("NATIVE arch reached linker, should have been selected earlier");
break;
case COMPILE_TARGET_ARCH_MACOS_ARM64:
header.cputype = CPU_TYPE_ARM64;
header.cpusubtype = CPU_SUBTYPE_ARM64_ALL;
break;
case COMPILE_TARGET_ARCH_MACOS_X86_64:
header.cputype = CPU_TYPE_X86_64;
header.cpusubtype = CPU_SUBTYPE_X86_64_ALL;
todo("unsupported arch x86_64");
case COMPILE_TARGET_ARCH_EEP:
todo("mach-o does not support EEP");
break;
}
header.filetype = MH_OBJECT;
header.ncmds = 4;
header.sizeofcmds =
sizeof(struct segment_command_64) + sizeof(struct section_64) +
sizeof(struct section_64) + sizeof(struct build_version_command) +
sizeof(struct symtab_command) + sizeof(struct dysymtab_command);
header.flags = 0;
fwrite(&header, sizeof(header), 1, file);
}
#define ENCODE(x, y, z) ((x & 0xFF) << 16) | ((y & 0x0F) << 8) | (z & 0x0F)
#define ENCODE_MINOS(x, y, z) \
((x & 0xFF) << 16) | ((y & 0x0F) << 8) | (z & 0x0F)
#define ENCODE_SDK(x, y, z) ((x & 0xFF) << 16) | ((y & 0x0F) << 8) | (z & 0x0F)
void write_relocations(FILE *file, const struct build_object_args *args) {
// FIXME: currently str relocs are based on hardcoded indices that link the
// compiler/emitter/object builder they should probably go to a hashmap
// against id like how the other relocs work in current state, it is
// _required_ that you see all the SINGLE relocs before the PAIR relocs it
// goes symbols -> strings -> external symbols
size_t num_non_str_syms = 0;
for (size_t i = 0; i < args->num_symbols; i++) {
struct symbol *symbol = &args->symbols[i];
if (symbol->ty != SYMBOL_TY_STRING) {
num_non_str_syms++;
}
}
for (size_t i = 0; i < args->num_relocations; i++) {
struct relocation *reloc = &args->relocations[i];
switch (reloc->ty) {
case RELOCATION_TY_SINGLE: {
size_t index = SIZE_T_MAX;
// FIXME: lookup instead of this mess lolz
for (size_t i = 0; i < args->num_symbols; i++) {
struct symbol *symbol = &args->symbols[i];
if (strcmp(symbol->name, reloc->sym.symbol_name) == 0) {
index = i;
}
}
for (size_t i = 0; i < args->num_extern_symbols; i++) {
struct external_symbol *symbol = &args->extern_symbols[i];
if (strcmp(symbol->name, reloc->sym.symbol_name) == 0) {
index = args->num_symbols + i;
}
}
invariant_assert(index != SIZE_T_MAX, "could not find symbol for reloc");
struct relocation_info info = {.r_address = reloc->address,
.r_length = reloc->size,
.r_pcrel = 1,
.r_symbolnum = index,
.r_extern = 1,
.r_type = ARM64_RELOC_BRANCH26};
fwrite(&info, sizeof(info), 1, file);
break;
}
case RELOCATION_TY_PAIR: {
size_t index = num_non_str_syms + reloc->str.str_index;
struct relocation_info infos[2] = {
{.r_address = reloc->address,
.r_length = reloc->size,
.r_pcrel = 1,
.r_symbolnum = index,
.r_extern = 1,
.r_type = ARM64_RELOC_PAGE21},
{.r_address = reloc->address + 4,
.r_length = reloc->size,
.r_pcrel = 0,
.r_symbolnum = index,
.r_extern = 1,
.r_type = ARM64_RELOC_PAGEOFF12},
};
fwrite(infos, sizeof(infos), 1, file);
break;
}
}
}
}
void write_segment_command(FILE *file, const struct build_object_args *args) {
size_t total_str_size = 0;
for (size_t i = 0; i < args->num_strings; i++) {
total_str_size += strlen(args->strings[i]) + 1 /* null */;
}
total_str_size = ROUND_UP(total_str_size, 4);
struct segment_command_64 segment;
memset(&segment, 0, sizeof(segment));
segment.cmd = LC_SEGMENT_64;
segment.cmdsize = sizeof(segment) + sizeof(struct section_64) * 2;
strcpy(segment.segname, ""); // name can just be blank "__TEXT");
segment.vmaddr = 0;
segment.vmsize = args->len_data + total_str_size;
segment.fileoff =
sizeof(struct mach_header_64) + sizeof(struct segment_command_64) +
sizeof(struct section_64) + sizeof(struct section_64) +
sizeof(struct symtab_command) + sizeof(struct dysymtab_command) +
sizeof(struct build_version_command);
segment.filesize = args->len_data + total_str_size;
segment.maxprot = VM_PROT_READ | VM_PROT_WRITE | VM_PROT_EXECUTE;
segment.initprot = VM_PROT_READ | VM_PROT_WRITE | VM_PROT_EXECUTE;
segment.nsects = 2;
segment.flags = 0;
struct section_64 text;
memset(&text, 0, sizeof(text));
strcpy(text.sectname, "__text");
strcpy(text.segname, "__TEXT");
text.addr = 0;
text.size = args->len_data;
text.offset = segment.fileoff;
text.align = 4;
text.reloff = segment.fileoff + text.size + total_str_size;
text.nreloc = args->num_relocation_instrs;
text.flags = S_REGULAR | S_ATTR_PURE_INSTRUCTIONS; /*| S_ATTR_EXT_RELOC;*/
text.reserved1 = 0;
text.reserved2 = 0;
text.reserved3 = 0;
struct section_64 cstrings;
memset(&cstrings, 0, sizeof(cstrings));
strcpy(cstrings.sectname, "__cstring");
strcpy(cstrings.segname, "__TEXT");
cstrings.addr = text.size;
cstrings.size = total_str_size;
cstrings.offset = segment.fileoff + text.size;
cstrings.align = 0;
cstrings.reloff = 0; // no relocs
cstrings.nreloc = 0;
cstrings.flags = S_CSTRING_LITERALS; // | S_ATTR_EXT_RELOC;
cstrings.reserved1 = 0;
cstrings.reserved2 = 0;
cstrings.reserved3 = 0;
struct build_version_command version;
version.cmd = LC_BUILD_VERSION;
version.cmdsize = sizeof(version);
version.platform = PLATFORM_MACOS;
version.minos = ENCODE_MINOS(12, 0, 0);
version.sdk = ENCODE_SDK(0, 0, 0);
version.ntools = 0;
struct symtab_command symtab;
memset(&symtab, 0, sizeof(symtab));
symtab.cmd = LC_SYMTAB;
symtab.cmdsize = sizeof(symtab);
symtab.symoff = segment.fileoff + text.size + cstrings.size +
sizeof(struct relocation_info) * args->num_relocation_instrs;
debug("num symbols %d", args->num_symbols);
symtab.nsyms = args->num_symbols + args->num_extern_symbols;
symtab.stroff = symtab.symoff + sizeof(struct nlist_64) * symtab.nsyms;
size_t total_str_len = 0;
for (size_t i = 0; i < args->num_symbols; i++) {
debug("symbol %s", args->symbols[i].name);
total_str_len += strlen(args->symbols[i].name);
total_str_len++; // null terminator
}
for (size_t i = 0; i < args->num_extern_symbols; i++) {
debug("external symbol %s", args->extern_symbols[i].name);
total_str_len += strlen(args->extern_symbols[i].name);
total_str_len++; // null terminator
}
symtab.strsize = total_str_len;
// "local" symbols are debugging
// "external" symbols are what we call symbols
// "undefined" symbols are what we call external symbols
struct dysymtab_command dysymtab;
memset(&dysymtab, 0, sizeof(dysymtab));
dysymtab.cmd = LC_DYSYMTAB;
dysymtab.cmdsize = sizeof(dysymtab);
dysymtab.iextdefsym = 0;
dysymtab.nextdefsym = args->num_symbols;
dysymtab.iundefsym = args->num_symbols;
dysymtab.nundefsym = args->num_extern_symbols;
fwrite(&segment, sizeof(segment), 1, file);
fwrite(&text, sizeof(text), 1, file);
fwrite(&cstrings, sizeof(cstrings), 1, file);
fwrite(&version, sizeof(version), 1, file);
fwrite(&symtab, sizeof(symtab), 1, file);
fwrite(&dysymtab, sizeof(dysymtab), 1, file);
/* C Strings */
fseek(file, cstrings.offset, SEEK_SET);
for (size_t i = 0; i < args->num_strings; i++) {
fwrite(args->strings[i], 1, strlen(args->strings[i]) + 1, file);
}
/* Data */
fseek(file, text.offset, SEEK_SET);
fwrite(args->data, 1, args->len_data, file);
/* Relocations */
fseek(file, text.reloff, SEEK_SET);
write_relocations(file, args);
/* Symbol table */
fseek(file, symtab.symoff, SEEK_SET);
size_t str_off = 1; // first index is just a `null` char
for (size_t i = 0; i < args->num_symbols; i++) {
struct symbol *symbol = &args->symbols[i];
uint8_t n_sect;
uint64_t n_value;
uint8_t n_type;
switch (symbol->ty) {
case SYMBOL_TY_FUNC:
n_sect = 1;
n_value = symbol->value;
break;
case SYMBOL_TY_STRING:
n_sect = 2;
n_value = symbol->value + args->len_data;
break;
}
switch (symbol->visibility) {
case SYMBOL_VISIBILITY_GLOBAL:
n_type = N_SECT | N_EXT;
break;
case SYMBOL_VISIBILITY_PRIVATE:
n_type = N_SECT;
break;
}
struct nlist_64 nlist;
nlist.n_un.n_strx = str_off;
nlist.n_type = n_type;
nlist.n_sect = n_sect;
nlist.n_desc = 0;
nlist.n_value = n_value;
str_off += strlen(symbol->name) + 1;
fwrite(&nlist, sizeof(nlist), 1, file);
}
for (size_t i = 0; i < args->num_extern_symbols; i++) {
struct external_symbol *symbol = &args->extern_symbols[i];
struct nlist_64 nlist;
nlist.n_un.n_strx = str_off;
nlist.n_type = N_UNDF | N_EXT;
nlist.n_sect = NO_SECT;
nlist.n_desc = 0;
nlist.n_value = 0;
str_off += strlen(symbol->name) + 1;
fwrite(&nlist, sizeof(nlist), 1, file);
}
char null = 0;
fwrite(&null, sizeof(null), 1, file);
/* String table */
for (size_t i = 0; i < args->num_symbols; i++) {
struct symbol *symbol = &args->symbols[i];
fwrite(symbol->name, strlen(symbol->name) + 1, 1, file);
}
for (size_t i = 0; i < args->num_extern_symbols; i++) {
struct external_symbol *symbol = &args->extern_symbols[i];
fwrite(symbol->name, strlen(symbol->name) + 1, 1, file);
}
}
void write_macho(const struct build_object_args *args) {
FILE *file = fopen(args->output, "wb");
if (file == NULL) {
perror("fopen");
exit(EXIT_FAILURE);
}
write_mach_header(file, args->compile_args);
write_segment_command(file, args);
fclose(file);
}