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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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13
cmd/w6a/parse.c
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@@ -121,6 +121,7 @@ opcode_lookup(const char *m)
{ "TEXT", A_TEXT },
{ "DATA", A_DATA },
{ "DATAW", A_DATAW },
{ "DATAR", A_DATAR },
{ NULL, 0 }
};
for (int i = 0; tab[i].m; i++)
@@ -211,6 +212,17 @@ parse_operand(Asm *a, const char *s, Aoperand *out)
while (a_isidcont((unsigned char)*s) && n < 63) buf[n++] = *s++;
buf[n] = 0;
/* Optional `+disp` between the ident and `(SB)`. Used by
* DATAR to address bytes inside an existing .data slot
* (e.g. `DATAR s+8(SB),...`). */
i64 sym_disp = 0;
if (*s == '+') {
s++;
char *end;
sym_disp = a_parsenum(s, &end);
s = end;
}
/* ID(SB) means external symbol */
if (*s == '(') {
char rbuf[8] = {0};
@@ -223,6 +235,7 @@ parse_operand(Asm *a, const char *s, Aoperand *out)
if (r == D_PSB) {
out->type = D_EXTERN;
out->sym = strdup(buf);
out->offset = sym_disp;
return 0;
}
out->type = D_INDIR;