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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
Download Patch File Download Diff File Expand all files Collapse all files

37
cmd/w6a/asm.c
View File

@@ -70,6 +70,23 @@ a_addreloc(Asm *a, u64 off, int kind, Asym *s, i64 add)
{
Areloc *r = calloc(1, sizeof *r);
r->off = off;
r->section = 0; /* .text */
r->kind = kind;
r->sym = s;
r->addend = add;
r->next = a->relocs;
a->relocs = r;
}
/* Record a relocation that lives in the .data section. Used by
* DATAR to patch a 64-bit slot with a symbol's runtime VA. obj.c
* separates these into .rela.data when emitting the .o. */
void
a_addreloc_data(Asm *a, u64 off, int kind, Asym *s, i64 add)
{
Areloc *r = calloc(1, sizeof *r);
r->off = off;
r->section = 1; /* .data */
r->kind = kind;
r->sym = s;
r->addend = add;
@@ -335,6 +352,26 @@ a_encode(Asm *a)
a_emit_data_byte(a, p->bytes[i]);
break;
}
case A_DATAR: {
/* DATAR slot+off(SB), target(SB) — record an
* R_X86_64_64 relocation at slot+off in .data
* pointing at target. The slot must already be
* defined by a prior DATAW (which emitted zero
* placeholder bytes the linker will overwrite). */
Asym *holder = a_intern(a, p->from.sym);
if (!holder->defined || !holder->is_data) {
fprintf(stderr,
"w6a: line %d: DATAR slot %s not yet defined as DATAW\n",
p->line, p->from.sym);
a->errs++;
break;
}
Asym *target = a_intern(a, p->to.sym);
u64 reloff = holder->addr + (u64)p->from.offset;
a_addreloc_data(a, reloff, 1 /* R_X86_64_64 */,
target, 0);
break;
}
case A_RET:
a_emit_byte(a, 0xC3);
break;