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//: Beginnings of a nicer way to build SubX programs.
//: We're going to question every notion, including "Assembly language" and
//: "compiler".
//: Motto: Abstract nothing, check everything.
//:
//: Workflow: read 'source' file. Run a series of transforms on it, each
//: passing through what it doesn't understand. The final program should be
//: just machine code, suitable to write to an ELF binary.
:(before "End Main")
if (is_equal(argv[1], "translate")) {
assert(argc > 3);
program p;
ifstream fin(argv[2]);
parse(fin, p);
if (trace_contains_errors()) return 1;
transform(p);
if (trace_contains_errors()) return 1;
dump_elf(p, argv[3]);
}
:(code)
// write out a program to a bare-bones ELF file
void dump_elf(const program& p, const char* filename) {
ofstream out(filename, ios::binary);
dump_elf_header(out, p);
for (size_t i = 0; i < p.segments.size(); ++i)
dump_segment(p.segments.at(i), out);
out.close();
}
void dump_elf_header(ostream& out, const program& p) {
char c = '\0';
#define O(X) c = (X); out.write(&c, sizeof(c))
// host is required to be little-endian
#define emit(X) out.write(reinterpret_cast<const char*>(&X), sizeof(X))
//// ehdr
// e_ident
O(0x7f); O(/*E*/0x45); O(/*L*/0x4c); O(/*F*/0x46);
O(0x1); // 32-bit format
O(0x1); // little-endian
O(0x1); O(0x0);
for (size_t i = 0; i < 8; ++i) { O(0x0); }
// e_type
O(0x02); O(0x00);
// e_machine
O(0x03); O(0x00);
// e_version
O(0x01); O(0x00); O(0x00); O(0x00);
// e_entry
int e_entry = p.segments.at(0).start; // convention
emit(e_entry);
// e_phoff -- immediately after ELF header
int e_phoff = 0x34;
emit(e_phoff);
// e_shoff; unused
int dummy32 = 0;
emit(dummy32);
// e_flags; unused
emit(dummy32);
// e_ehsize
uint16_t e_ehsize = 0x34;
emit(e_ehsize);
// e_phentsize
uint16_t e_phentsize = 0x20;
emit(e_phentsize);
// e_phnum
uint16_t e_phnum = SIZE(p.segments);
emit(e_phnum);
// e_shentsize
uint16_t dummy16 = 0x0;
emit(dummy16);
// e_shnum
emit(dummy16);
// e_shstrndx
emit(dummy16);
uint32_t p_offset = /*size of ehdr*/0x34 + SIZE(p.segments)*0x20/*size of each phdr*/;
for (int i = 0; i < SIZE(p.segments); ++i) {
//// phdr
// p_type
uint32_t p_type = 0x1;
emit(p_type);
// p_offset
emit(p_offset);
// p_vaddr
emit(e_entry);
// p_paddr
emit(e_entry);
// p_filesz
uint32_t size = size_of(p.segments.at(i));
assert(size < SEGMENT_SIZE);
emit(size);
// p_memsz
emit(size);
// p_flags
uint32_t p_flags = (i == 0) ? /*r-x*/0x5 : /*rw-*/0x6; // convention: only first segment is code
emit(p_flags);
// p_align
uint32_t p_align = 0x4;
emit(p_align);
// prepare for next segment
p_offset += size;
}
#undef O
#undef emit
}
void dump_segment(const segment& s, ostream& out) {
for (int i = 0; i < SIZE(s.lines); ++i) {
const vector<word>& w = s.lines.at(i).words;
for (int j = 0; j < SIZE(w); ++j) {
uint8_t x = hex_byte(w.at(j).data); // we're done with metadata by this point
out.write(reinterpret_cast<const char*>(&x), /*sizeof(byte)*/1);
}
}
}
uint32_t size_of(const segment& s) {
uint32_t sum = 0;
for (int i = 0; i < SIZE(s.lines); ++i)
sum += SIZE(s.lines.at(i).words);
return sum;
}
:(before "End Includes")
using std::ios;
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