ww/selfhost/cmd/w6l/pass.ww

// selfhost/cmd/w6l/pass.ww — port of cmd/w6l/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).

package w6l;

import os;
import sym;
import dyn;

def R_X86_64_64:    i32 = 1;
def R_X86_64_PC32:  i32 = 2;
def R_X86_64_PLT32: i32 = 4;

export fn resolve(l: *lnk) i32 = {
	// Initialise dynamic-linking sentinels. alloc(T{})! zeroes, so
	// isdyn/dynlib start clean — but pltidx and dynsymidx
	// must be -1, not 0.
	let si: *lsym = l.syms;
	for (si != nil) {
		si.pltidx = -1;
		si.dynsymidx = -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) {
				if (r.sym.isdyn == 0) {
					let so: *lso = l.sos;
					for (so != nil) {
						if (soprovides(so, r.sym.name) != 0) {
							r.sym.isdyn = 1;
							r.sym.dynlib = so;
							r.sym.pltidx = l.dynn;
							l.dynn += 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.isdyn == 0) {
					os.write(2, "w6l: 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 patchu32(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;
};

fn patchu64(p: *u8, v: u64) void = {
	let i: i32 = 0;
	for (i < 8) {
		p[i] = ((v >> (i: u64 * 8u64)) & 255u64): u8;
		i += 1;
	};
};

export fn relocate(l: *lnk, textva: u64, datava: 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.isdyn != 0) {
				r = r.rnext;
				continue;
			};
			if (r.sym.defined != 0) {
				let symva: u64 = textva + r.sym.val;
				if (r.sym.indata != 0) { symva = datava + r.sym.val; };
				let k: i32 = r.kind;
				if (k == R_X86_64_PC32) {
					let site: u64 = textva + r.off;
					let rel: i64 = (symva: i64 - site: i64) + r.addend;
					patchu32(l.text + r.off, rel: u32);
				} else { if (k == R_X86_64_PLT32) {
					let site: u64 = textva + r.off;
					let rel: i64 = (symva: i64 - site: i64) + r.addend;
					patchu32(l.text + r.off, rel: u32);
				} else { if (k == R_X86_64_64) {
					// Absolute 64-bit. Currently used only
					// for DATAR slots in .data.
					let v: u64 = (symva: i64 + r.addend): u64;
					if (r.section == 1) {
						patchu64(l.data + r.off, v);
					} else {
						patchu64(l.text + r.off, v);
					};
				} else {
					os.write(2, "w6l: unsupported reloc kind\n".ptr, 27u64);
					l.errs += 1;
				};};};
			};
		};
		r = r.rnext;
	};
	return l.errs;
};