ww/selfhost/cmd/6l/main.combined.ww

// os — process and filesystem facade. The body of each call lands
// either in libwwrt.a (rt_syscall trampoline) or libc bindings,
// depending on how the program was linked.

@symbol("rt_syscall") fn syscall0(num: i64) i64;
@symbol("rt_syscall") fn syscall1(num: i64, a: i64) i64;
@symbol("rt_syscall") fn syscall2(num: i64, a: i64, b: i64) i64;
@symbol("rt_syscall") fn syscall3(num: i64, a: i64, b: i64, c: i64) i64;

@symbol("rt_alloc") fn alloc(n: u64) *void;
@symbol("rt_free")  fn free(p: *void, n: u64) void;
@symbol("rt_abort") fn abort(msg: str) void;

// Hare-style runtime check. Caller passes a message that's printed
// to stderr before exit(1).
export fn assert(cond: bool, msg: str) void = {
	if (!cond) { abort(msg); };
};

def SYS_READ:  i64 = 0;
def SYS_WRITE: i64 = 1;
def SYS_OPEN:  i64 = 2;
def SYS_CLOSE: i64 = 3;
def SYS_LSEEK: i64 = 8;
def SYS_EXIT:  i64 = 60;

// open(2) flags. Linux values, matching <fcntl.h>.
def O_RDONLY: i32 = 0;
def O_WRONLY: i32 = 1;
def O_RDWR:   i32 = 2;
def O_CREAT:  i32 = 64;		// 0x40
def O_TRUNC:  i32 = 512;	// 0x200

// lseek(2) whence.
def SEEK_SET: i32 = 0;
def SEEK_CUR: i32 = 1;
def SEEK_END: i32 = 2;

export fn exit(code: i32) void = {
	syscall1(SYS_EXIT, code: i64);
};

// Raw, non-fallible primitives. These return Linux's int conventions
// (negative = -errno, non-negative = bytes/fd/etc). Callers wanting a
// Hare-style fallible API use the wrappers below.
export fn write(fd: i32, buf: *u8, n: u64) i64 = {
	return syscall3(SYS_WRITE, fd: i64, buf: i64, n: i64);
};

export fn read(fd: i32, buf: *u8, n: u64) i64 = {
	return syscall3(SYS_READ, fd: i64, buf: i64, n: i64);
};

export fn close(fd: i32) i32 = {
	return syscall1(SYS_CLOSE, fd: i64): i32;
};

// Fallible wrappers. The error variant is a plain str (Plan 9 errstr
// model, see lib/errors); the sum type makes success/failure explicit
// without overloading length-zero.
export fn tryread(fd: i32, buf: *u8, n: u64) (i64 | str) = {
	let r: i64 = read(fd, buf, n);
	if (r < 0) { return "read failed"; };
	return r;
};

export fn trywrite(fd: i32, buf: *u8, n: u64) (i64 | str) = {
	let r: i64 = write(fd, buf, n);
	if (r < 0) { return "write failed"; };
	return r;
};

// open — Linux open(2). Path must be NUL-terminated; callers using ww
// `str` must ensure the bytes are followed by a 0 byte (literals are,
// arena-copied paths usually are by construction). Returns -errno on
// failure, fd otherwise. Higher-level callers prefer `tryopen`.
export fn open(path: *u8, flags: i32, mode: i32) i32 = {
	return syscall3(SYS_OPEN, path: i64, flags: i64, mode: i64): i32;
};

export fn tryopen(path: *u8, flags: i32, mode: i32) (i32 | str) = {
	let fd: i32 = open(path, flags, mode);
	if (fd < 0) { return "open failed"; };
	return fd;
};

// lseek — set/inspect the fd's position. Returns the new offset or
// a negative errno. We use this for fstat-free file-size discovery
// (open ⇒ lseek to end ⇒ lseek back).
export fn lseek(fd: i32, off: i64, whence: i32) i64 = {
	return syscall3(SYS_LSEEK, fd: i64, off, whence: i64);
};

// filesize — convenience: returns the byte length of an open fd by
// seeking to the end and back. -1 on error.
export fn filesize(fd: i32) i64 = {
	let end: i64 = lseek(fd, 0i64, SEEK_END);
	if (end < 0) { return -1i64; };
	let r: i64 = lseek(fd, 0i64, SEEK_SET);
	if (r < 0) { return -1i64; };
	return end;
};

// readfull — keep reading until `n` bytes have arrived or the fd
// closes early. Returns bytes read (0..=n) or -1 on read error.
export fn readfull(fd: i32, buf: *u8, n: u64) i64 = {
	let got: u64 = 0u64;
	for (got < n) {
		let r: i64 = read(fd, buf + got, n - got);
		if (r < 0) { return -1i64; };
		if (r == 0) { return got: i64; };	// short read: caller decides
		got += r: u64;
	};
	return got: i64;
};

// writefull — keep writing until `n` bytes have been accepted or the
// fd refuses progress. Returns bytes written or -1.
export fn writefull(fd: i32, buf: *u8, n: u64) i64 = {
	let sent: u64 = 0u64;
	for (sent < n) {
		let r: i64 = write(fd, buf + sent, n - sent);
		if (r < 0) { return -1i64; };
		if (r == 0) { return sent: i64; };
		sent += r: u64;
	};
	return sent: i64;
};

// selfhost/cmd/wwc/mem.ww — port of cmd/wwc/mem.c.
//
// Bump arena allocator. Backed by the runtime page allocator
// (rt_alloc / rt_free), no libc. Each chunk is mmap'd; when the
// current chunk runs out we link a fresh one. Freeing the arena
// unmaps the chain.
//
// Memory handed out is 16-byte aligned. The C version under
// cmd/wwc/ is retained until the three-stage bootstrap diffs clean.

use os;

def ALIGN: u64       = 16u64;
def INIT_CHUNK: u64  = 65536u64;
def MAX_CHUNK: u64   = 4194304u64;
def ARENA_SZ: u64    = 48u64;	// sizeof(arena), kept in sync below

type arena = struct {
	buf:   *u8,
	off:   u64,
	cap:   u64,
	next:  *arena,
	total: u64,
};

fn roundup(n: u64, a: u64) u64 = {
	return (n + a - 1u64) & ~(a - 1u64);
};

export fn newarena() *arena = {
	let a: *arena = os.alloc(ARENA_SZ): *arena;
	a.buf = os.alloc(INIT_CHUNK): *u8;
	a.off = 0u64;
	a.cap = INIT_CHUNK;
	a.next = nil;
	a.total = 0u64;
	return a;
};

// Grow: link a fresh chunk in front of the head. We push the old
// chunk into `next` so the head always describes the current bump
// region. Chunk size doubles up to MAX_CHUNK.
fn grow(a: *arena, need: u64) bool = {
	let want: u64 = a.cap * 2u64;
	if (want < need) { want = need; };
	if (want > MAX_CHUNK) { want = MAX_CHUNK; };
	if (want < need) { return false; };	// single allocation too big

	let old: *arena = os.alloc(ARENA_SZ): *arena;
	old.buf = a.buf;
	old.off = a.off;
	old.cap = a.cap;
	old.next = a.next;
	old.total = 0u64;

	a.buf = os.alloc(want): *u8;
	a.off = 0u64;
	a.cap = want;
	a.next = old;
	return true;
};

export fn amalloc(a: *arena, n: u64) *void = {
	let need: u64 = roundup(n, ALIGN);
	if (need > a.cap - a.off) {
		if (!grow(a, need)) { return nil; };
	};
	let p: *u8 = a.buf + a.off;
	a.off += need;
	a.total += need;
	// Zero the region. Plan 9 amalloc zeroes; we mirror that here so
	// the checker can assume freshly allocated nodes start at 0.
	let i: u64 = 0u64;
	for (i < need) {
		p[i] = 0u8;
		i += 1u64;
	};
	return p: *void;
};

// astrndup — copy `n` bytes into the arena and produce a NUL-terminated
// view. Returns a `str` whose ptr is arena-owned and whose len is `n`
// (the trailing NUL is past `len`, so callers reading exactly n bytes
// see no padding). Used by the lexer to capture token text.
export fn astrndup(a: *arena, src: *u8, n: u64) str = {
	let p: *u8 = amalloc(a, n + 1u64): *u8;
	let i: u64 = 0u64;
	for (i < n) {
		p[i] = src[i];
		i += 1u64;
	};
	p[n] = 0u8;
	let r: str;
	r.ptr = p;
	r.len = n: i32;
	return r;
};

export fn freearena(a: *arena) void = {
	for (a != nil) {
		let next: *arena = a.next;
		os.free(a.buf: *void, a.cap);
		os.free(a: *void, ARENA_SZ);
		a = next;
	};
};

// selfhost/cmd/6l/sym.ww — port of cmd/6l/sym.c.
//
// Linker symbol table. Singly-linked list, usually a few hundred
// entries; hashing isn't worth it yet.

use mem;

type lsym = struct {
	name:     str,
	val:      u64,	// offset within combined .text once linked
	defined:  i32,	// 1 if some lobj defines this symbol
	owner:    *lobj,
	idx_in_owner: i32,
	snext:    *lsym,
};

type lrel = struct {
	off:    u64,	// offset within combined .text
	kind:   i32,	// R_X86_64_*
	sym:    *lsym,
	addend: i64,
	rnext:  *lrel,
};

type lobj = struct {
	path:      str,
	buf:       *u8,	// object bytes
	len:       u64,
	text_off:  u64,	// offset of .text in combined output
	text_size: u64,
	onext:     *lobj,
};

type lnk = struct {
	a:       *arena,
	objs:    *lobj,
	syms:    *lsym,
	rels:    *lrel,
	text:    *u8,	// combined .text
	textcap: u64,
	textlen: u64,
	errs:    i32,
};

fn streq(a: str, b: str) bool = {
	if (a.len != b.len) { return false; };
	let i: i32 = 0;
	for (i < a.len) {
		if (a[i] != b[i]) { return false; };
		i += 1;
	};
	return true;
};

export fn l_intern(l: *lnk, name: str) *lsym = {
	let s: *lsym = l.syms;
	for (s != nil) {
		if (streq(s.name, name)) { return s; };
		s = s.snext;
	};
	let n: *lsym = amalloc(l.a, 64u64): *lsym;
	n.name = name;
	n.snext = l.syms;
	l.syms = n;
	return n;
};

export fn l_lookup(l: *lnk, name: str) *lsym = {
	let s: *lsym = l.syms;
	for (s != nil) {
		if (streq(s.name, name)) { return s; };
		s = s.snext;
	};
	return nil;
};

// selfhost/cmd/6l/obj.ww — port of cmd/6l/obj.c.
//
// Loads relocatable ELF64 .o files emitted by 6a, appends .text to
// the combined image, and pulls in symbols + relocations with
// offsets adjusted to the combined section.
//
// Also handles SysV `ar` archives (libwwrt.a). The two-pass loader
// indexes members on the first pass and iteratively pulls members
// that define currently-undefined symbols on subsequent passes.

use os;
use mem;
use sym;

def ET_REL:        i32 = 1;
def EM_X86_64:     i32 = 62;
def SHT_PROGBITS:  i32 = 1;
def SHT_SYMTAB:    i32 = 2;
def SHT_STRTAB:    i32 = 3;
def SHT_RELA:      i32 = 4;

// ---- little-endian byte readers ----------------------------------------
// 6a/6l use straight LE on amd64. Reading via byte offsets keeps us off
// the cgen's u16 field-load story for now (MOVZBQ exists; MOVZWQ doesn't).

fn rd_u16(p: *u8, off: u64) u16 = {
	let b0: u16 = p[off]: u16;
	let b1: u16 = p[off + 1u64]: u16;
	return b0 | (b1 << 8u16);
};

fn rd_u32(p: *u8, off: u64) u32 = {
	let b0: u32 = p[off]: u32;
	let b1: u32 = p[off + 1u64]: u32;
	let b2: u32 = p[off + 2u64]: u32;
	let b3: u32 = p[off + 3u64]: u32;
	return b0 | (b1 << 8u32) | (b2 << 16u32) | (b3 << 24u32);
};

fn rd_u64(p: *u8, off: u64) u64 = {
	let lo: u64 = rd_u32(p, off): u64;
	let hi: u64 = rd_u32(p, off + 4u64): u64;
	return lo | (hi << 32u64);
};

// ---- ELF64 section header offsets (40 bytes total) --------------------
def SHDR_SIZE:     u64 = 64u64;	// sizeof(Shdr) per ELF64 spec
def SHDR_NAME:     u64 = 0u64;
def SHDR_TYPE:     u64 = 4u64;
def SHDR_OFFSET:   u64 = 24u64;
def SHDR_SIZE_F:   u64 = 32u64;
def SHDR_LINK:     u64 = 40u64;

// ELF64 ehdr field offsets
def EHDR_SIZE:     u64 = 64u64;
def EHDR_TYPE:     u64 = 16u64;
def EHDR_MACHINE:  u64 = 18u64;
def EHDR_SHOFF:    u64 = 40u64;
def EHDR_SHENTSIZE: u64 = 58u64;
def EHDR_SHNUM:    u64 = 60u64;
def EHDR_SHSTRNDX: u64 = 62u64;

// ELF64 sym entry: 24 bytes
def SYM_SIZE:      u64 = 24u64;
def SYM_NAME:      u64 = 0u64;
def SYM_INFO:      u64 = 4u64;
def SYM_SHNDX:     u64 = 6u64;
def SYM_VALUE:     u64 = 8u64;

// ELF64 RELA entry: 24 bytes
def RELA_SIZE:     u64 = 24u64;
def RELA_OFFSET:   u64 = 0u64;
def RELA_INFO:     u64 = 8u64;
def RELA_ADDEND:   u64 = 16u64;

// ---- file slurp --------------------------------------------------------

fn read_all(path_cs: *u8) (*u8, u64) = {
	let fd: i32 = os.open(path_cs, os.O_RDONLY, 0i32);
	if (fd < 0) { return nil, 0u64; };
	let n: i64 = os.filesize(fd);
	if (n < 0i64) { os.close(fd); return nil, 0u64; };
	let buf: *u8 = os.alloc(n: u64): *u8;
	let got: i64 = os.readfull(fd, buf, n: u64);
	os.close(fd);
	if (got != n) { return nil, 0u64; };
	return buf, n: u64;
};

// ---- text buffer growth ------------------------------------------------

fn emit_text(l: *lnk, src: *u8, n: u64) void = {
	if (l.textlen + n > l.textcap) {
		let nc: u64 = l.textcap;
		if (nc == 0u64) { nc = 4096u64; };
		for (nc < l.textlen + n) { nc = nc * 2u64; };
		// Grow by mmap'ing a fresh region and copying. The old buffer
		// is leaked into the page allocator; for a linker run this is
		// trivial waste.
		let nb: *u8 = os.alloc(nc): *u8;
		let i: u64 = 0u64;
		for (i < l.textlen) {
			nb[i] = l.text[i];
			i += 1u64;
		};
		l.text = nb;
		l.textcap = nc;
	};
	let i: u64 = 0u64;
	for (i < n) {
		l.text[l.textlen + i] = src[i];
		i += 1u64;
	};
	l.textlen += n;
};

// ---- C-string helpers --------------------------------------------------

fn cstrlen(p: *u8) u64 = {
	let n: u64 = 0u64;
	for (p[n] != 0u8) { n += 1u64; };
	return n;
};

fn cstr_eq(p: *u8, lit: str) bool = {
	let n: u64 = lit.len: u64;
	let i: u64 = 0u64;
	for (i < n) {
		let li: i32 = i: i32;
		if (p[i] != lit[li]) { return false; };
		i += 1u64;
	};
	if (p[i] != 0u8) { return false; };
	return true;
};

// Build a ww str from a NUL-terminated *u8 (for passing to l_intern).
fn cstr_to_str(a: *arena, p: *u8) str = {
	let n: u64 = cstrlen(p);
	return astrndup(a, p, n);
};

// ---- archive (SysV ar) types and helpers -------------------------------
//
// Each archive member starts with a 60-byte ar_hdr. The fields we care
// about are the first byte (member type) and the size at offset 48 (a
// 10-byte, space-padded decimal). Member bodies are 2-byte aligned.

type defent = struct {
	name:  str,
	dnext: *defent,
};

type armember = struct {
	data:   *u8,		// arena copy of the member's ELF bytes
	size:   u64,
	defs:   *defent,	// linked list of defined globals
	loaded: i32,
	mnext:  *armember,
};

fn is_archive(p: *u8, len: u64) bool = {
	if (len < 8u64) { return false; };
	if (p[0u64] != 33u8)  { return false; };	// '!'
	if (p[1u64] != 60u8)  { return false; };	// '<'
	if (p[2u64] != 97u8)  { return false; };	// 'a'
	if (p[3u64] != 114u8) { return false; };	// 'r'
	if (p[4u64] != 99u8)  { return false; };	// 'c'
	if (p[5u64] != 104u8) { return false; };	// 'h'
	if (p[6u64] != 62u8)  { return false; };	// '>'
	if (p[7u64] != 10u8)  { return false; };	// '\n'
	return true;
};

// ar_field — parse a space-padded decimal integer of width n.
fn ar_field(p: *u8, n: u64) u64 = {
	let v: u64 = 0u64;
	let i: u64 = 0u64;
	for (i < n) {
		let c: u8 = p[i];
		if (c < 48u8) { return v; };	// space, NUL, etc.
		if (c > 57u8) { return v; };
		v = v * 10u64 + ((c - 48u8): u64);
		i += 1u64;
	};
	return v;
};

// elf_globals — return a linked list of names of globally-defined
// (STB_GLOBAL) symbols whose section is `.text`. Names are arena
// copies, so the source ELF buffer can be freed afterward.
fn elf_globals(a: *arena, buf: *u8, len: u64) *defent = {
	if (len < EHDR_SIZE) { return nil; };
	if (buf[0u64] != 127u8) { return nil; };
	if (buf[1u64] != 69u8)  { return nil; };
	if (buf[2u64] != 76u8)  { return nil; };
	if (buf[3u64] != 70u8)  { return nil; };

	let shoff:    u64 = rd_u64(buf, EHDR_SHOFF);
	let shnum:    u32 = rd_u16(buf, EHDR_SHNUM): u32;
	let shstrndx: u32 = rd_u16(buf, EHDR_SHSTRNDX): u32;

	let shstr_sh_off: u64 = rd_u64(buf, shoff + (shstrndx: u64) * SHDR_SIZE + SHDR_OFFSET);
	let shstr: *u8 = buf + shstr_sh_off;

	let idx_text:   i32 = -1;
	let idx_symtab: i32 = -1;
	let i: u32 = 0u32;
	for (i < shnum) {
		let sh_off: u64 = shoff + (i: u64) * SHDR_SIZE;
		let sh_type: u32 = rd_u32(buf, sh_off + SHDR_TYPE);
		let sh_name: u32 = rd_u32(buf, sh_off + SHDR_NAME);
		let nm: *u8 = shstr + (sh_name: u64);
		if (sh_type == SHT_PROGBITS: u32) {
			if (cstr_eq(nm, ".text")) { idx_text = i: i32; };
		};
		if (sh_type == SHT_SYMTAB: u32)  { idx_symtab = i: i32; };
		i += 1u32;
	};
	if (idx_text < 0) { return nil; };
	if (idx_symtab < 0) { return nil; };

	let sym_sh:   u64 = shoff + (idx_symtab: u64) * SHDR_SIZE;
	let sym_off:  u64 = rd_u64(buf, sym_sh + SHDR_OFFSET);
	let sym_size: u64 = rd_u64(buf, sym_sh + SHDR_SIZE_F);
	let sym_link: u32 = rd_u32(buf, sym_sh + SHDR_LINK);
	let nsyms:    u64 = sym_size / SYM_SIZE;

	let str_sh:  u64 = shoff + (sym_link: u64) * SHDR_SIZE;
	let str_off: u64 = rd_u64(buf, str_sh + SHDR_OFFSET);
	let strtab:  *u8 = buf + str_off;

	let head: *defent = nil;
	let si: u64 = 1u64;
	for (si < nsyms) {
		let sym_p: u64 = sym_off + si * SYM_SIZE;
		let st_name:  u32 = rd_u32(buf, sym_p + SYM_NAME);
		let st_info:  u8  = buf[sym_p + SYM_INFO];
		let st_shndx: u16 = rd_u16(buf, sym_p + SYM_SHNDX);
		let bind:     u32 = (st_info: u32) >> 4u32;
		// STB_GLOBAL = 1; defined in .text.
		if (bind == 1u32) {
			if (st_shndx != 0u16) {
				if ((st_shndx: i32) == idx_text) {
					let nm_p: *u8 = strtab + (st_name: u64);
					if (nm_p[0u64] != 0u8) {
						let nm: str = cstr_to_str(a, nm_p);
						let de: *defent = amalloc(a, 32u64): *defent;
						de.name = nm;
						de.dnext = head;
						head = de;
					};
				};
			};
		};
		si += 1u64;
	};
	return head;
};

// member_defines_undef — true if any of m's defined globals matches a
// currently-undefined symbol in the linker's symbol table. Names not
// already interned are uninteresting (the link doesn't need them yet).
fn member_defines_undef(l: *lnk, m: *armember) bool = {
	let de: *defent = m.defs;
	for (de != nil) {
		let s: *lsym = l_lookup(l, de.name);
		if (s != nil) {
			if (s.defined == 0) { return true; };
		};
		de = de.dnext;
	};
	return false;
};

// load_archive — port of cmd/6l/obj.c:load_archive.
//
// Pass 1 indexes every regular member. Pass 2 iteratively pulls in any
// member that supplies a currently-undefined symbol; each pull may
// introduce fresh undefs, so we loop until quiescent.
fn load_archive(l: *lnk, path_cs: *u8, buf: *u8, len: u64) i32 = {
	let head: *armember = nil;
	let tail: *armember = nil;
	let pos:  u64 = 8u64;	// past "!<arch>\n"
	for (pos + 60u64 <= len) {
		let hdr_size: u64 = ar_field(buf + pos + 48u64, 10u64);
		let hdr_end:  u64 = pos + 60u64;
		if (hdr_end + hdr_size > len) { break; };
		let first: u8 = buf[pos];
		// Skip the symbol table ('/'), long-name table ('//'), and
		// any padding entries (NUL or space leading byte).
		if (first != 47u8) { if (first != 0u8) { if (first != 32u8) {
			let m: *armember = amalloc(l.a, 48u64): *armember;
			m.size = hdr_size;
			let mb: *u8 = amalloc(l.a, hdr_size): *u8;
			let i: u64 = 0u64;
			for (i < hdr_size) {
				mb[i] = buf[hdr_end + i];
				i += 1u64;
			};
			m.data = mb;
			m.defs = elf_globals(l.a, mb, hdr_size);
			m.loaded = 0;
			m.mnext = nil;
			if (head == nil) { head = m; }
			else { tail.mnext = m; };
			tail = m;
		}; }; };
		pos = hdr_end + hdr_size;
		if ((hdr_size & 1u64) != 0u64) { pos = pos + 1u64; };
	};

	let changed: i32 = 1;
	for (changed != 0) {
		changed = 0;
		let m: *armember = head;
		for (m != nil) {
			if (m.loaded == 0) {
				if (member_defines_undef(l, m)) {
					if (load_image(l, path_cs, m.data, m.size) == 0) {
						m.loaded = 1;
						changed = 1;
					};
				};
			};
			m = m.mnext;
		};
	};
	return 0;
};

// ---- main loader -------------------------------------------------------

export fn l_load(l: *lnk, path_cs: *u8) i32 = {
	let bufp: *u8;
	let buflen: u64;
	bufp, buflen = read_all(path_cs);
	if (bufp == nil) {
		os.write(2, "6l: cannot read object\n".ptr, 23u64);
		return -1;
	};
	if (is_archive(bufp, buflen)) {
		return load_archive(l, path_cs, bufp, buflen);
	};
	return load_image(l, path_cs, bufp, buflen);
};

fn load_image(l: *lnk, path_cs: *u8, buf: *u8, len: u64) i32 = {
	if (len < EHDR_SIZE) { return -1; };
	// magic: 0x7f, 'E', 'L', 'F'
	if (buf[0u64] != 127u8) { return -1; };
	if (buf[1u64] != 69u8)  { return -1; };
	if (buf[2u64] != 76u8)  { return -1; };
	if (buf[3u64] != 70u8)  { return -1; };
	if (buf[4u64] != 2u8)   { return -1; };	// ELFCLASS64
	if (rd_u16(buf, EHDR_TYPE)    != ET_REL: u16)    { return -1; };
	if (rd_u16(buf, EHDR_MACHINE) != EM_X86_64: u16) { return -1; };

	let shoff:    u64 = rd_u64(buf, EHDR_SHOFF);
	let shnum:    u32 = rd_u16(buf, EHDR_SHNUM): u32;
	let shstrndx: u32 = rd_u16(buf, EHDR_SHSTRNDX): u32;

	let shstr_sh_off: u64 = rd_u64(buf, shoff + (shstrndx: u64) * SHDR_SIZE + SHDR_OFFSET);
	let shstr: *u8 = buf + shstr_sh_off;

	// find .text, .symtab, .rela.text
	let idx_text:   i32 = -1;
	let idx_symtab: i32 = -1;
	let idx_rela:   i32 = -1;
	let i: u32 = 0u32;
	for (i < shnum) {
		let sh_off: u64 = shoff + (i: u64) * SHDR_SIZE;
		let sh_type: u32 = rd_u32(buf, sh_off + SHDR_TYPE);
		let sh_name: u32 = rd_u32(buf, sh_off + SHDR_NAME);
		let nm: *u8 = shstr + (sh_name: u64);
		if (sh_type == SHT_PROGBITS: u32) {
			if (cstr_eq(nm, ".text")) { idx_text = i: i32; };
		};
		if (sh_type == SHT_SYMTAB: u32)  { idx_symtab = i: i32; };
		if (sh_type == SHT_RELA: u32) {
			if (cstr_eq(nm, ".rela.text")) { idx_rela = i: i32; };
		};
		i += 1u32;
	};
	if (idx_text < 0) {
		os.write(2, "6l: missing .text\n".ptr, 18u64);
		return -1;
	};
	if (idx_symtab < 0) {
		os.write(2, "6l: missing .symtab\n".ptr, 20u64);
		return -1;
	};

	let text_sh:   u64 = shoff + (idx_text: u64) * SHDR_SIZE;
	let text_off:  u64 = rd_u64(buf, text_sh + SHDR_OFFSET);
	let text_size: u64 = rd_u64(buf, text_sh + SHDR_SIZE_F);

	let sym_sh:   u64 = shoff + (idx_symtab: u64) * SHDR_SIZE;
	let sym_off:  u64 = rd_u64(buf, sym_sh + SHDR_OFFSET);
	let sym_size: u64 = rd_u64(buf, sym_sh + SHDR_SIZE_F);
	let sym_link: u32 = rd_u32(buf, sym_sh + SHDR_LINK);
	let nsyms:    u64 = sym_size / SYM_SIZE;

	let str_sh:  u64 = shoff + (sym_link: u64) * SHDR_SIZE;
	let str_off: u64 = rd_u64(buf, str_sh + SHDR_OFFSET);
	let strtab:  *u8 = buf + str_off;

	// Track this object.
	let ob: *lobj = amalloc(l.a, 64u64): *lobj;
	ob.path = cstr_to_str(l.a, path_cs);
	ob.buf = buf;
	ob.len = len;
	ob.text_off = l.textlen;
	ob.text_size = text_size;
	ob.onext = l.objs;
	l.objs = ob;

	// Append .text bytes to the combined image.
	emit_text(l, buf + text_off, text_size);

	// Walk symbols. We don't keep a per-object map[] of *lsym. Instead
	// the reloc loop re-walks symtab and re-interns by name. Simpler
	// than dancing around the cgen's u64-shift gaps.
	let si: u64 = 1u64;	// skip index 0 (always undef sentinel)
	for (si < nsyms) {
		let sym_p: u64 = sym_off + si * SYM_SIZE;
		let st_name:  u32 = rd_u32(buf, sym_p + SYM_NAME);
		let st_shndx: u16 = rd_u16(buf, sym_p + SYM_SHNDX);
		let st_value: u64 = rd_u64(buf, sym_p + SYM_VALUE);
		let nm_p: *u8 = strtab + (st_name: u64);
		if (nm_p[0u64] != 0u8) {
			let nm: str = cstr_to_str(l.a, nm_p);
			let gs: *lsym = l_intern(l, nm);
			if (st_shndx != 0u16) {
				if ((st_shndx: i32) == idx_text) {
					if (gs.defined != 0) {
						os.write(2, "6l: duplicate symbol\n".ptr, 21u64);
						l.errs += 1;
					} else {
						gs.defined = 1;
						gs.owner = ob;
						gs.idx_in_owner = si: i32;
						gs.val = ob.text_off + st_value;
					};
				};
			};
		};
		si += 1u64;
	};

	// Per-object relocation collection.
	if (idx_rela >= 0) {
		let rela_sh:   u64 = shoff + (idx_rela: u64) * SHDR_SIZE;
		let rela_off:  u64 = rd_u64(buf, rela_sh + SHDR_OFFSET);
		let rela_size: u64 = rd_u64(buf, rela_sh + SHDR_SIZE_F);
		let nrel:      u64 = rela_size / RELA_SIZE;
		let ri: u64 = 0u64;
		for (ri < nrel) {
			let rp: u64 = rela_off + ri * RELA_SIZE;
			let r_off:    u64 = rd_u64(buf, rp + RELA_OFFSET);
			let r_info:   u64 = rd_u64(buf, rp + RELA_INFO);
			let r_addend: u64 = rd_u64(buf, rp + RELA_ADDEND);
			let r_sym_idx: u32 = (r_info >> 32u64): u32;
			let r_kind:    i32 = ((r_info & 4294967295u64): u32): i32;
			let nr: *lrel = amalloc(l.a, 48u64): *lrel;
			nr.off = ob.text_off + r_off;
			nr.kind = r_kind;
			nr.addend = r_addend: i64;
			// Look up the referenced sym by name (re-walk symtab).
			if ((r_sym_idx: u64) < nsyms) {
				let s_p: u64 = sym_off + (r_sym_idx: u64) * SYM_SIZE;
				let s_name: u32 = rd_u32(buf, s_p + SYM_NAME);
				let s_nm: *u8 = strtab + (s_name: u64);
				if (s_nm[0u64] != 0u8) {
					let nm: str = cstr_to_str(l.a, s_nm);
					nr.sym = l_intern(l, nm);
				};
			};
			nr.rnext = l.rels;
			l.rels = nr;
			ri += 1u64;
		};
	};

	return 0;
};

// selfhost/cmd/6l/pass.ww — port of cmd/6l/pass.c.
//
// Resolution + relocation. l_resolve flags every undefined symbol
// referenced by a relocation. l_relocate walks the rel list and
// patches the .text bytes in place once the final virtual base is
// known. Supported relocation kinds: PC32 (=2), PLT32 (=4); both
// are 32-bit PC-relative displacements (PLT32 == PC32 for static).

use os;
use sym;

def R_X86_64_PC32:  i32 = 2;
def R_X86_64_PLT32: i32 = 4;

export fn l_resolve(l: *lnk) i32 = {
	let r: *lrel = l.rels;
	for (r != nil) {
		if (r.sym != nil) {
			if (r.sym.defined == 0) {
				os.write(2, "6l: undefined reference to '".ptr, 28u64);
				let nm: str = r.sym.name;
				os.write(2, nm.ptr, nm.len: u64);
				os.write(2, "'\n".ptr, 2u64);
				l.errs += 1;
			};
		};
		r = r.rnext;
	};
	return l.errs;
};

fn patch_u32(p: *u8, v: u32) void = {
	p[0] = (v & 255u32): u8;
	p[1] = ((v >> 8u32) & 255u32): u8;
	p[2] = ((v >> 16u32) & 255u32): u8;
	p[3] = ((v >> 24u32) & 255u32): u8;
};

export fn l_relocate(l: *lnk, base: u64) i32 = {
	let r: *lrel = l.rels;
	for (r != nil) {
		if (r.sym != nil) {
			if (r.sym.defined != 0) {
				let k: i32 = r.kind;
				if (k == R_X86_64_PC32) {
					let site: u64 = base + r.off;
					let target: i64 = (base + r.sym.val): i64;
					let rel: i64 = (target - site: i64) + r.addend;
					patch_u32(l.text + r.off, rel: u32);
				} else { if (k == R_X86_64_PLT32) {
					let site: u64 = base + r.off;
					let target: i64 = (base + r.sym.val): i64;
					let rel: i64 = (target - site: i64) + r.addend;
					patch_u32(l.text + r.off, rel: u32);
				} else {
					os.write(2, "6l: unsupported reloc kind\n".ptr, 27u64);
					l.errs += 1;
				};};
			};
		};
		r = r.rnext;
	};
	return l.errs;
};

// selfhost/cmd/6l/out.ww — port of cmd/6l/out.c.
//
// Emit a static ELF64 executable. File layout (per the C original):
//   [0..64)       Ehdr
//   [64..120)     Phdr (one PT_LOAD)
//   [120..0x1000) zero pad
//   [0x1000..)    .text bytes
// Single PT_LOAD covers the whole file, R+X. No interpreter, no .bss.

use os;
use sym;

def ET_EXEC:    u16 = 2u16;
def EM_X86_64_W: u16 = 62u16;
def EV_CURRENT: u32 = 1u32;
def ELFCLASS64: u8 = 2u8;
def ELFDATA2LSB: u8 = 1u8;
def PT_LOAD:    u32 = 1u32;
def PF_X:       u32 = 1u32;
def PF_R:       u32 = 4u32;

def TEXT_OFF: u64 = 4096u64;	// 0x1000

// ---- little-endian byte writers ----------------------------------------

fn wr_u16(buf: *u8, off: u64, v: u16) void = {
	buf[off]         = (v & 255u16): u8;
	buf[off + 1u64]  = ((v >> 8u16) & 255u16): u8;
};

fn wr_u32(buf: *u8, off: u64, v: u32) void = {
	buf[off]         = (v & 255u32): u8;
	buf[off + 1u64]  = ((v >> 8u32)  & 255u32): u8;
	buf[off + 2u64]  = ((v >> 16u32) & 255u32): u8;
	buf[off + 3u64]  = ((v >> 24u32) & 255u32): u8;
};

fn wr_u64(buf: *u8, off: u64, v: u64) void = {
	wr_u32(buf, off,        (v & 4294967295u64): u32);
	wr_u32(buf, off + 4u64, ((v >> 32u64) & 4294967295u64): u32);
};

// ---- emit ---------------------------------------------------------------

export fn l_emit_elf(l: *lnk, fd: i32, base: u64, entry: u64) i32 = {
	let filesz: u64 = TEXT_OFF + l.textlen;

	// One contiguous header buffer covering [0..0x1000), then .text.
	let hdr: *u8 = os.alloc(TEXT_OFF): *u8;	// zero-initialised by mmap

	// --- Ehdr (64 bytes) ---
	hdr[0u64] = 127u8;	// 0x7f
	hdr[1u64] = 69u8;	// 'E'
	hdr[2u64] = 76u8;	// 'L'
	hdr[3u64] = 70u8;	// 'F'
	hdr[4u64] = ELFCLASS64;
	hdr[5u64] = ELFDATA2LSB;
	hdr[6u64] = EV_CURRENT: u8;
	wr_u16(hdr, 16u64, ET_EXEC);		// e_type
	wr_u16(hdr, 18u64, EM_X86_64_W);	// e_machine
	wr_u32(hdr, 20u64, EV_CURRENT);		// e_version
	wr_u64(hdr, 24u64, entry);		// e_entry
	wr_u64(hdr, 32u64, 64u64);		// e_phoff = sizeof(Ehdr)
	wr_u64(hdr, 40u64, 0u64);		// e_shoff
	wr_u32(hdr, 48u64, 0u32);		// e_flags
	wr_u16(hdr, 52u64, 64u16);		// e_ehsize
	wr_u16(hdr, 54u64, 56u16);		// e_phentsize
	wr_u16(hdr, 56u64, 1u16);		// e_phnum
	wr_u16(hdr, 58u64, 0u16);		// e_shentsize
	wr_u16(hdr, 60u64, 0u16);		// e_shnum
	wr_u16(hdr, 62u64, 0u16);		// e_shstrndx

	// --- Phdr (56 bytes) at offset 64 ---
	wr_u32(hdr, 64u64, PT_LOAD);		// p_type
	wr_u32(hdr, 68u64, PF_R | PF_X);	// p_flags
	wr_u64(hdr, 72u64, 0u64);		// p_offset
	wr_u64(hdr, 80u64, base);		// p_vaddr
	wr_u64(hdr, 88u64, base);		// p_paddr
	wr_u64(hdr, 96u64, filesz);		// p_filesz
	wr_u64(hdr, 104u64, filesz);		// p_memsz
	wr_u64(hdr, 112u64, TEXT_OFF);		// p_align

	// Write [0..0x1000) then .text.
	let n1: i64 = os.writefull(fd, hdr, TEXT_OFF);
	if (n1 != TEXT_OFF: i64) { return -1; };
	if (l.textlen > 0u64) {
		let n2: i64 = os.writefull(fd, l.text, l.textlen);
		if (n2 != l.textlen: i64) { return -1; };
	};
	return 0;
};

// selfhost/cmd/6l/main.ww — port of cmd/6l/main.c.
//
// 6l = amd64 static linker. Reads relocatable ELF .o files and
// SysV `ar` archives, resolves symbols, applies relocations, writes
// a static ELF executable.
//
//   6l_ww -o out file1.o file2.o libwwrt.a ...

use os;
use mem;
use sym;
use obj;
use pass;
use out;

def BASE: u64 = 4194304u64;	// 0x400000
def CODE_VA_OFF: u64 = 4096u64;	// .text starts at base + 0x1000

// Linker context lives in main's frame; arena gets passed in.
fn make_lnk(a: *arena) *lnk = {
	let l: *lnk = amalloc(a, 96u64): *lnk;
	l.a = a;
	return l;
};

fn streq_cs(a: *u8, lit: str) bool = {
	let n: u64 = lit.len: u64;
	let i: u64 = 0u64;
	for (i < n) {
		let li: i32 = i: i32;
		if (a[i] != lit[li]) { return false; };
		i += 1u64;
	};
	if (a[i] != 0u8) { return false; };
	return true;
};

export fn main(argc: i32, argv: **u8) i32 = {

	let out_path: *u8 = nil;
	// Inputs: store as **u8 (heap'd from a fixed-size buffer).
	let max_inputs: i32 = 64;
	let inputs: **u8 = os.alloc((max_inputs: u64) * 8u64): **u8;
	let ninputs: i32 = 0;

	let i: i32 = 1;
	for (i < argc) {
		let a: *u8 = argv[i];
		if (streq_cs(a, "-o")) {
			i += 1;
			if (i >= argc) {
				os.write(2, "6l: -o requires argument\n".ptr, 25u64);
				return 2;
			};
			out_path = argv[i];
		} else { if (a[0u64] == 45u8) {
			os.write(2, "6l: unknown flag\n".ptr, 17u64);
			return 2;
		} else {
			if (ninputs >= max_inputs) {
				os.write(2, "6l: too many inputs\n".ptr, 20u64);
				return 2;
			};
			inputs[ninputs] = a;
			ninputs += 1;
		}; };
		i += 1;
	};

	if (out_path == nil) {
		os.write(2, "usage: 6l_ww -o exe file1.o [file2.o...]\n".ptr, 41u64);
		return 2;
	};
	if (ninputs == 0) {
		os.write(2, "6l: no inputs\n".ptr, 14u64);
		return 2;
	};

	let a: *arena = newarena();
	let l: *lnk = make_lnk(a);

	// Seed _start so a libwwrt-style start.o is recognised as wanted.
	l_intern(l, "_start");

	let k: i32 = 0;
	for (k < ninputs) {
		if (l_load(l, inputs[k]) != 0) {
			return 1;
		};
		k += 1;
	};

	if (l_resolve(l) != 0) { return 1; };
	if (l_relocate(l, BASE + CODE_VA_OFF) != 0) { return 1; };

	let entry_sym: *lsym = l_lookup(l, "_start");
	if (entry_sym == nil) { entry_sym = l_lookup(l, "main"); }
	else { if (entry_sym.defined == 0) { entry_sym = l_lookup(l, "main"); }; };
	if (entry_sym == nil) {
		os.write(2, "6l: no _start or main symbol\n".ptr, 29u64);
		return 1;
	};
	if (entry_sym.defined == 0) {
		os.write(2, "6l: no _start or main symbol\n".ptr, 29u64);
		return 1;
	};

	// Open output: O_WRONLY|O_CREAT|O_TRUNC, mode 0755.
	let flags: i32 = os.O_WRONLY | os.O_CREAT | os.O_TRUNC;
	let fd: i32 = os.open(out_path, flags, 493i32);	// 0o755
	if (fd < 0) {
		os.write(2, "6l: cannot open output\n".ptr, 23u64);
		return 1;
	};

	let entry_va: u64 = BASE + CODE_VA_OFF + entry_sym.val;
	let rc: i32 = l_emit_elf(l, fd, BASE, entry_va);
	os.close(fd);
	return rc;
};