/*
 * pass.c — resolution + relocation. After all objects are loaded:
 *
 *   l_resolve : check that every symbol referenced by a relocation
 *               is defined somewhere. Errors get logged.
 *   l_relocate: with the final virtual base address known, walk the
 *               relocation list and patch the .text bytes in place.
 *
 * Supported relocation kinds: PC32 (2), PLT32 (4). Both are PC-relative
 * 32-bit displacements; for static linking PLT32 collapses to PC32.
 */
#include "l.h"
#include <stdio.h>
#include <string.h>

#define R_X86_64_PC32	2
#define R_X86_64_PLT32	4

int
l_resolve(Lnk *l)
{
	/* Initialise dynamic-linking fields. plt_idx and dynsym_idx
	 * default to -1; l_intern sets is_dyn/dyn_lib to 0/NULL via
	 * calloc, but we make the invariants explicit here for clarity. */
	for (Lsym *s = l->syms; s; s = s->next) {
		s->plt_idx = -1;
		s->dynsym_idx = -1;
	}

	/* Promote each undefined sym that some Lso exports to "dynamic"
	 * and hand it a PLT slot. Order is the iteration order over the
	 * relocation list; that determines slot numbering and is stable
	 * across runs (rels are pushed onto the head as objects load). */
	for (Lrel *r = l->rels; r; r = r->next) {
		if (r->sym == NULL || r->sym->defined) continue;
		if (r->sym->is_dyn) continue;	/* already promoted */
		for (Lso *so = l->sos; so; so = so->next) {
			const char *ver = NULL;
			if (l_so_provides_v(so, r->sym->name, &ver)) {
				r->sym->is_dyn = 1;
				r->sym->dyn_lib = so;
				r->sym->dyn_version = ver;	/* may be NULL */
				r->sym->plt_idx = l->dyn_n++;
				break;
			}
		}
	}

	/* What remains undefined truly is undefined. */
	for (Lrel *r = l->rels; r; r = r->next) {
		if (r->sym == NULL) continue;
		if (!r->sym->defined && !r->sym->is_dyn) {
			fprintf(stderr, "w6l: undefined reference to '%s'\n",
			    r->sym->name);
			l->errs++;
		}
	}
	return l->errs;
}

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

int
l_relocate(Lnk *l, u64 base)
{
	for (Lrel *r = l->rels; r; r = r->next) {
		if (r->sym == NULL) continue;
		/* Dynamic syms are patched later, in l_emit_elf, once the
		 * PLT's virtual address is known. */
		if (r->sym->is_dyn) continue;
		if (!r->sym->defined) continue;
		switch (r->kind) {
		case R_X86_64_PC32:
		case R_X86_64_PLT32: {
			u64 site = base + r->off;
			i64 target = (i64)(base + r->sym->val);
			i64 rel = target - (i64)site + r->addend;
			patch_u32(l->text + r->off, (u32)(i32)rel);
			break;
		}
		default:
			fprintf(stderr, "w6l: unsupported reloc kind %d\n",
			    r->kind);
			l->errs++;
		}
	}
	return l->errs;
}