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w6a+w6l: DATAR directive for absolute-address relocs in .data

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Unblock literal initialisers for str/slice/struct globals by wiring
an R_X86_64_64 relocation kind through both assembler and static
linker.

w6a:
  - new A_DATAR directive, syntax `DATAR slot+off(SB),target(SB)`,
    records an R_X86_64_64 reloc at slot+off in .data pointing at
    target. The slot must be pre-defined by a prior DATAW;
  - parse_operand learned the `name+disp(SB)` shape so the slot's
    byte offset can be addressed explicitly;
  - Areloc carries a `section` flag (0=.text / 1=.data) and obj.c
    splits the reloc list into .rela.text and .rela.data, emitting
    the latter conditionally with sh_info pointing at .data.

w6l:
  - Lrel grows the same `section` flag; obj.c loads `.rela.data`
    sections into the global reloc list with offsets shifted by
    each input's data_off;
  - pass.c handles R_X86_64_64: target VA is data_va+sym.val for
    in_data symbols (else text_va+sym.val), addend is added, and
    the 8-byte slot is patched in l->data (or l->text).

Inputs without DATAR are unaffected — bootstrap, 991 (selfhost .o
diff) and 992 (selfhost exe diff) keep their byte-identical
output. 520_datar covers the new path: asm a DATAW+DATAR pair,
verify .rela.data has exactly one R_X86_64_64 entry, link, run,
confirm the relocated pointer feeds a 5-byte write that prints
"hello".

Selfhost mirror + w6c emission for str/slice/struct literal init
land in follow-ups.
This commit is contained in:
Hojun-Cho
2026-05-12 12:45:11 +09:00
parent 00d1120441
commit d998425391
11 changed files with 353 additions and 21 deletions
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26
cmd/w6l/obj.c
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@@ -278,9 +278,10 @@ load_image(Lnk *l, const char *path, u8 *buf, u64 len)
if (eh->e_shstrndx >= eh->e_shnum) { free(buf); return -1; }
const char *shstr = (const char *)(buf + sh[eh->e_shstrndx].sh_offset);
/* find .text, .data (optional), .symtab, .strtab, .rela.text */
/* find .text, .data (optional), .symtab, .strtab, .rela.text,
* .rela.data (optional) */
int idx_text = -1, idx_data = -1, idx_symtab = -1, idx_strtab = -1;
int idx_rela = -1;
int idx_rela = -1, idx_relad = -1;
for (u16 i = 0; i < eh->e_shnum; i++) {
const char *nm = shstr + sh[i].sh_name;
if (sh[i].sh_type == SHT_PROGBITS && strcmp(nm, ".text") == 0)
@@ -291,6 +292,8 @@ load_image(Lnk *l, const char *path, u8 *buf, u64 len)
idx_symtab = i;
else if (sh[i].sh_type == SHT_RELA && strcmp(nm, ".rela.text") == 0)
idx_rela = i;
else if (sh[i].sh_type == SHT_RELA && strcmp(nm, ".rela.data") == 0)
idx_relad = i;
}
if (idx_text < 0 || idx_symtab < 0) {
fprintf(stderr, "w6l: %s: missing .text or .symtab\n", path);
@@ -356,6 +359,25 @@ load_image(Lnk *l, const char *path, u8 *buf, u64 len)
for (u64 i = 0; i < nrel; i++) {
Lrel *r = calloc(1, sizeof *r);
r->off = ob->text_off + rt[i].r_offset;
r->section = 0;
r->kind = (int)ELF64_R_TYPE(rt[i].r_info);
u32 sidx = ELF64_R_SYM(rt[i].r_info);
r->sym = (sidx < nsyms) ? map[sidx] : NULL;
r->addend = rt[i].r_addend;
r->next = l->rels;
l->rels = r;
}
}
/* per-object: collect data relocations from .rela.data. The
* .data section in the .o starts at a per-object 0; we shift
* by ob->data_off so r->off indexes the combined .data buffer. */
if (idx_relad >= 0) {
Rela64 *rt = (Rela64 *)(buf + sh[idx_relad].sh_offset);
u64 nrel = sh[idx_relad].sh_size / sizeof(Rela64);
for (u64 i = 0; i < nrel; i++) {
Lrel *r = calloc(1, sizeof *r);
r->off = ob->data_off + rt[i].r_offset;
r->section = 1;
r->kind = (int)ELF64_R_TYPE(rt[i].r_info);
u32 sidx = ELF64_R_SYM(rt[i].r_info);
r->sym = (sidx < nsyms) ? map[sidx] : NULL;