A bare cross-module value-global load mis-qualified its symbol: cgen
mangled it with curmod via a non-preferring leaf lookup, so an exported
`let v` in module aa emitted both its DATA storage AND its bare-load as
main.v, colliding with main's private v. aa.getv() returned 99, not 7.
Functions were already correct (they thread a cur_mod hint via mafn /
emitfnname); value-globals did not. Both stages emitted IDENTICAL wrong
asm, so the byte-id gate was blind to it; combined.ww (frontend) is clean
-- the bug is purely in cgen. This is the cgen residual of #55 (#1 cgen
value-global module-qualifier).
Fix, symmetric in cmd/w6c/cgen.c + selfhost/cmd/wcc/{cgen,cgenexpr}.ww:
reference-site mangle uses the resolved module (curmod-prefer for bare
idents); definition/DATA-site mangle uses the decl's own module
(d->module / d.nmod) -- threaded per-site the way fns already do, via
mahint / emitsymnamehint. The fn-mangle path is left byte-for-byte
untouched.
Deviation from the signed-off spec (ratified by rob-pike after this
finding): the spec prescribed reusing the fn lookup (mod_mangle_fn /
modlookupforfn), but its first-match fallback mis-fires for value-
globals -- mod_collect export-skips exported non-fn decls (cgen.c:1059)
to keep their bare-name data ABI, so an exported leaf is absent from the
module map and the fallback grabs another module's same-leaf private
global. The value path therefore uses a distinct exact-(name,module)-or-
bare lookup (mod_lookup_value / modlookupvalue): mangle only on an exact
match, else stay bare. Byte-id-neutral on all existing single-owner code;
exported globals stay bare (ABI preserved), private stay module-qualified.
Honest boundary (rule 7): if two modules BOTH export the same value leaf,
both stay bare and the linker sees a duplicate symbol -- a correct, loud,
link-time ABI clash (like C), NOT a silent miscompile; left to the
linker, not papered over with a cgen heuristic.
Test: test/wcc/795_xmod_valglobal_run.c -- runtime (the exported global
read returns its own value, not the colliding private one) + cs==ww
byte-id, across i32-let / def-const / f64-let. Sibling to the checker
test 794_xmod_ident_prefer, which deliberately omitted byte-id because
this cgen bug diverged the asm independently.
Hojun-Cho
8481a05c3a