// selfhost/cmd/6l/pass.ww — port of cmd/6l/pass.c.
//
// Resolution + relocation. l_resolve flags every undefined symbol
// referenced by a relocation, and promotes those provided by some
// loaded .so to "dynamic" with a freshly-assigned PLT slot.
// l_relocate walks the rel list and patches the .text bytes in place
// once the final virtual base is known. Dynamic refs are deferred:
// their site is patched later in dynout, once the PLT vaddr is known.
//
// Supported relocation kinds: PC32 (=2), PLT32 (=4); both are 32-bit
// PC-relative displacements (PLT32 == PC32 for static).

use os;
use sym;
use dyn;

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

export fn l_resolve(l: *lnk) i32 = {
	// Initialise dynamic-linking sentinels. amalloc zeroes, so
	// is_dyn/dyn_lib start clean — but plt_idx and dynsym_idx
	// must be -1, not 0.
	let si: *lsym = l.syms;
	for (si != nil) {
		si.plt_idx = -1;
		si.dynsym_idx = -1;
		si = si.snext;
	};

	// Promote each undefined sym that some lso exports to dynamic
	// and hand it a PLT slot. Iteration order over the relocation
	// list determines slot numbering and is stable across runs.
	let r: *lrel = l.rels;
	for (r != nil) {
		if (r.sym != nil) {
			if (r.sym.defined == 0) {
				let sym: *lsym = r.sym;
				if (sym.is_dyn == 0) {
					let so: *lso = l.sos;
					for (so != nil) {
						if (l_so_provides(so, sym.name) != 0) {
							sym.is_dyn = 1;
							sym.dyn_lib = so;
							sym.plt_idx = l.dyn_n;
							l.dyn_n += 1;
							so = nil;	// break
						} else {
							so = so.sonext;
						};
					};
				};
			};
		};
		r = r.rnext;
	};

	// What remains undefined truly is undefined.
	let r2: *lrel = l.rels;
	for (r2 != nil) {
		if (r2.sym != nil) {
			if (r2.sym.defined == 0) {
				if (r2.sym.is_dyn == 0) {
					os.write(2, "6l: undefined reference to '".ptr, 28u64);
					let nm: str = r2.sym.name;
					os.write(2, nm.ptr, nm.len: u64);
					os.write(2, "'\n".ptr, 2u64);
					l.errs += 1;
				};
			};
		};
		r2 = r2.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) {
			// Dynamic refs are patched later in dynout once the
			// PLT vaddr is known.
			if (r.sym.is_dyn != 0) {
				r = r.rnext;
				continue;
			};
			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;
};