commit 7a985cce08172385f81d3fa7e74540ffc3ed037a
parent 81d88fcf49dea5f3f1d389ac360bf7c588c9d3ff
Author: Ryan Sepassi <rsepassi@gmail.com>
Date: Fri, 5 Jun 2026 16:30:15 -0700
Defer O1 local static data symbols
Diffstat:
8 files changed, 196 insertions(+), 42 deletions(-)
diff --git a/doc/plan/TODO.md b/doc/plan/TODO.md
@@ -34,27 +34,31 @@ undefined `.Lcfblk.N` (visible via `kit nm`). O0 is fine (the block is kept).
The plain `goto *p; done:` form is also fine because `done` is a real goto
target, so its block is retained.
+This is distinct from the fixed `.Lkit_jt.*` / `.Lkit_ro.*` DCE leak class:
+those were unreferenced orphan data symbols minted before O1 replay. `.Lcfblk.N`
+is a referenced MC/code-label symbol; the object has live text relocations to
+it, so the linker is correctly rejecting the undefined symbol.
+
Minimal repro:
```c
-static int ext(void) { return 7; }
-int main(void) {
- int x;
-before:;
- x = ext();
-after:;
- void* lo = &&before; /* address-taken, never a goto target */
- void* hi = &&after;
- return (lo != hi) ? 42 : x;
-}
+int p(void) { L: return &&L != 0; }
+```
+
+This emits a live text relocation against an undefined `.Lcfblk.N` at O1 and
+`kit run -O1` fails to link. The same construct inside a dead inline is clean:
+
+```c
+static inline void *q(void) { L: return &&L; }
+int p(void) { return 0; }
```
-`kit run -O1` on the above fails to link; `kit run -O0` returns 42. Likely in
-the O1 CFG/block-merge passes (`src/opt/pass_cfg.c` / block dedup): a block that
-is only referenced by a label-address relocation must be pinned (not merged or
-dropped), or the relocation retargeted to the surviving block. Found while
-writing the backtrace anchor test (doc/plan/BACKTRACE.md); worked around there
-by anchoring on a function address instead of `&&label`.
+Likely in the O1 CFG/block-merge passes (`src/opt/pass_cfg.c` / block dedup):
+the target block of `IR_LOAD_LABEL_ADDR` must be treated as address-taken/live
+through CFG cleanup and native emission, or any CFG merge/elision must retarget
+the label-address relocation to the surviving block label. Found while writing
+the backtrace anchor test (doc/plan/BACKTRACE.md); worked around there by
+anchoring on a function address instead of `&&label`.
## `__kit_syscallN` (`rt/include/kit/syscall.h`) is declared/documented but unimplemented
diff --git a/src/cg/data.c b/src/cg/data.c
@@ -794,8 +794,8 @@ ObjSymId api_emit_label_table(KitCg* g, const Label* labels, u32 n) {
strbuf_put_u64(&name_sb, g->rodata_counter++);
name = pool_intern_slice(c->global, (Slice){.s = strbuf_cstr(&name_sb),
.len = strbuf_len(&name_sb)});
- sym = obj_symbol(g->obj, name, SB_LOCAL, SK_OBJ, OBJ_SEC_NONE, 0,
- (u64)n * (u64)c->target.ptr_size);
+ sym = obj_symbol_defer(g->obj, name, SB_LOCAL, SV_DEFAULT, SK_OBJ,
+ (u64)n * (u64)c->target.ptr_size);
if (sym == OBJ_SYM_NONE)
compiler_panic(c, g->cur_loc, "api_emit_label_table: symbol failed");
diff --git a/src/cg/memory.c b/src/cg/memory.c
@@ -73,6 +73,39 @@ void kit_cg_push_null(KitCg* g, KitCgTypeId ptr_type) {
api_push(g, api_make_sv(api_op_imm(0, ty), ty));
}
+static int api_const_data_can_defer(const KitCg* g) {
+ if (!g || g->opt_level < 1) return 0;
+ if (g->fn_ret_type == KIT_CG_TYPE_NONE) return 0;
+ if (g->data_sym != OBJ_SYM_NONE || g->data_sec != OBJ_SEC_NONE) return 0;
+ if (g->data_local_static_target || g->data_discard ||
+ g->data_tls_collect) {
+ return 0;
+ }
+ return g->target && g->target->local_static_data_begin &&
+ g->target->local_static_data_write &&
+ g->target->local_static_data_end;
+}
+
+static int api_const_data_emit_deferred(KitCg* g, ObjSymId sym,
+ KitCgTypeId type, const uint8_t* data,
+ size_t len, uint32_t align) {
+ CGLocalStaticDataDesc desc;
+ KitCgDataDefAttrs data_attrs;
+ if (!api_const_data_can_defer(g)) return 0;
+ memset(&data_attrs, 0, sizeof data_attrs);
+ data_attrs.flags = KIT_CG_DATADEF_FUNCTION_LOCAL | KIT_CG_DATADEF_READONLY;
+ data_attrs.align = align;
+ memset(&desc, 0, sizeof desc);
+ desc.sym = sym;
+ desc.type = type;
+ desc.attrs = data_attrs;
+ desc.align = align;
+ if (!g->target->local_static_data_begin(g->target, &desc)) return 0;
+ if (len) g->target->local_static_data_write(g->target, data, (u64)len);
+ g->target->local_static_data_end(g->target);
+ return 1;
+}
+
KitCgSym kit_cg_const_data(KitCg* g, const uint8_t* data, size_t len,
uint32_t align, KitCgTypeId pointee_type) {
Compiler* c;
@@ -86,30 +119,39 @@ KitCgSym kit_cg_const_data(KitCg* g, const uint8_t* data, size_t len,
Sym anon_name;
ObjSymId sym;
KitCgDecl attrs;
+ int defer;
if (!g) return KIT_CG_SYM_NONE;
c = g->c;
ob = g->obj;
pty = resolve_type(c, pointee_type);
if (!pty) return KIT_CG_SYM_NONE;
+ align = align ? align : (u32)abi_cg_alignof(c->abi, pointee_type);
sec_name = pool_intern_slice(c->global, SLICE_LIT(".rodata"));
- sec = obj_section(ob, sec_name, SEC_RODATA, SF_ALLOC,
- align ? align : (u32)abi_cg_alignof(c->abi, pointee_type));
- base = obj_align_to(
- ob, sec, align ? align : (u32)abi_cg_alignof(c->abi, pointee_type));
- obj_write(ob, sec, data, len);
strbuf_init(&name_sb, name_buf, sizeof(name_buf));
strbuf_put_slice(&name_sb, SLICE_LIT(".Lkit_ro."));
strbuf_put_u64(&name_sb, g->rodata_counter++);
anon_name = pool_intern_slice(
c->global,
(Slice){.s = strbuf_cstr(&name_sb), .len = strbuf_len(&name_sb)});
- sym = obj_symbol(ob, anon_name, SB_LOCAL, SK_OBJ, sec, base, (u64)len);
+ defer = api_const_data_can_defer(g);
+ sym = defer ? obj_symbol_defer(ob, anon_name, SB_LOCAL, SV_DEFAULT, SK_OBJ,
+ (u64)len)
+ : obj_symbol(ob, anon_name, SB_LOCAL, SK_OBJ, OBJ_SEC_NONE, 0,
+ (u64)len);
+ if (sym == OBJ_SYM_NONE)
+ compiler_panic(c, g->cur_loc, "kit_cg_const_data: symbol failed");
memset(&attrs, 0, sizeof(attrs));
attrs.kind = KIT_CG_DECL_OBJECT;
attrs.sym.bind = KIT_SB_LOCAL;
attrs.sym.visibility = KIT_CG_VIS_DEFAULT;
attrs.as.object.flags = KIT_CG_OBJ_READONLY;
api_remember_sym(g, sym, pty, attrs);
+ if (defer && api_const_data_emit_deferred(g, sym, pty, data, len, align))
+ return (KitCgSym)sym;
+ sec = obj_section(ob, sec_name, SEC_RODATA, SF_ALLOC, align);
+ base = obj_align_to(ob, sec, align);
+ obj_write(ob, sec, data, len);
+ obj_symbol_define_live(ob, sym, sec, base, (u64)len);
return (KitCgSym)sym;
}
diff --git a/src/cg/native_direct_target.c b/src/cg/native_direct_target.c
@@ -1179,8 +1179,8 @@ static void nd_local_static_data_label_addr(CgTarget* t, Label target,
static void nd_local_static_data_end(CgTarget* t) {
NativeDirectTarget* d = nd_of(t);
if (!d->local_static_active) return;
- obj_symbol_define(t->obj, d->local_static_sym, d->local_static_sec,
- d->local_static_base, d->local_static_size);
+ obj_symbol_define_live(t->obj, d->local_static_sym, d->local_static_sec,
+ d->local_static_base, d->local_static_size);
d->local_static_active = 0;
d->local_static_sec = OBJ_SEC_NONE;
d->local_static_sym = OBJ_SYM_NONE;
diff --git a/src/obj/obj.c b/src/obj/obj.c
@@ -519,15 +519,10 @@ void obj_patch(ObjBuilder* ob, ObjSecId id, u32 ofs, const void* data,
if (s) buf_patch(&s->bytes, ofs, data, n);
}
-ObjSymId obj_symbol(ObjBuilder* ob, Sym name, SymBind bind, SymKind kind,
- ObjSecId section_id, u64 value, u64 size) {
- return obj_symbol_ex(ob, name, bind, SV_DEFAULT, kind, section_id, value,
- size, 0);
-}
-
-ObjSymId obj_symbol_ex(ObjBuilder* ob, Sym name, SymBind bind, SymVis vis,
- SymKind kind, ObjSecId section_id, u64 value, u64 size,
- u64 common_align) {
+static ObjSymId obj_symbol_make(ObjBuilder* ob, Sym name, SymBind bind,
+ SymVis vis, SymKind kind,
+ ObjSecId section_id, u64 value, u64 size,
+ u64 common_align, int index_name) {
u32 id;
ObjSym* s = Symbols_push(&ob->symbols, &id);
if (!s) return OBJ_SYM_NONE;
@@ -543,16 +538,40 @@ ObjSymId obj_symbol_ex(ObjBuilder* ob, Sym name, SymBind bind, SymVis vis,
/* First-wins: record the lowest id for this name so obj_symbol_find returns
* the same symbol the linear scan would. Later same-name symbols (legal for
* STB_LOCAL) do not overwrite. */
- if (name && !SymNameIndex_get(&ob->sym_by_name, name))
+ if (index_name && name && !SymNameIndex_get(&ob->sym_by_name, name))
(void)SymNameIndex_set(&ob->sym_by_name, name, (ObjSymId)id);
return (ObjSymId)id;
}
+ObjSymId obj_symbol(ObjBuilder* ob, Sym name, SymBind bind, SymKind kind,
+ ObjSecId section_id, u64 value, u64 size) {
+ return obj_symbol_ex(ob, name, bind, SV_DEFAULT, kind, section_id, value,
+ size, 0);
+}
+
+ObjSymId obj_symbol_ex(ObjBuilder* ob, Sym name, SymBind bind, SymVis vis,
+ SymKind kind, ObjSecId section_id, u64 value, u64 size,
+ u64 common_align) {
+ return obj_symbol_make(ob, name, bind, vis, kind, section_id, value, size,
+ common_align, 1);
+}
+
+ObjSymId obj_symbol_defer(ObjBuilder* ob, Sym name, SymBind bind, SymVis vis,
+ SymKind kind, u64 size) {
+ ObjSymId id;
+ ObjSym* s;
+ id = obj_symbol_make(ob, name, bind, vis, kind, OBJ_SEC_NONE, 0, size, 0, 0);
+ if (id == OBJ_SYM_NONE) return OBJ_SYM_NONE;
+ s = Symbols_at(&ob->symbols, id);
+ if (s) s->removed = 1;
+ return id;
+}
+
ObjSymId obj_symbol_find(ObjBuilder* ob, Sym name) {
- /* Authoritative O(1) lookup — never a linear scan. Every symbol is created
- * through obj_symbol_ex (the only Symbols_push besides the id-0 sentinel),
- * which indexes it, and obj_symbol_rename keeps the index exact, so the map
- * always holds the first id for a live name. */
+ /* Authoritative O(1) lookup — never a linear scan. Normal/live symbols are
+ * indexed when created or published, and obj_symbol_rename keeps the index
+ * exact. Deferred symbols deliberately stay out of this map until published.
+ */
ObjSymId* hit;
if (!ob || !name) return OBJ_SYM_NONE;
hit = SymNameIndex_get(&ob->sym_by_name, name);
@@ -571,6 +590,22 @@ void obj_symbol_define(ObjBuilder* ob, ObjSymId id, ObjSecId section_id,
if (s->kind == SK_UNDEF) s->kind = SK_OBJ;
}
+void obj_symbol_define_live(ObjBuilder* ob, ObjSymId id, ObjSecId section_id,
+ u64 value, u64 size) {
+ ObjSym* s;
+ ObjSymId* slot;
+ obj_symbol_define(ob, id, section_id, value, size);
+ if (!ob || id == OBJ_SYM_NONE) return;
+ s = Symbols_at(&ob->symbols, id);
+ if (!s) return;
+ s->removed = 0;
+ if (s->name) {
+ slot = SymNameIndex_get(&ob->sym_by_name, s->name);
+ if (!slot || *slot > id)
+ (void)SymNameIndex_set(&ob->sym_by_name, s->name, id);
+ }
+}
+
void obj_symbol_set_flags(ObjBuilder* ob, ObjSymId id, u16 flags) {
ObjSym* s;
if (id == OBJ_SYM_NONE) return;
diff --git a/src/obj/obj.h b/src/obj/obj.h
@@ -448,6 +448,11 @@ ObjSymId obj_symbol(ObjBuilder*, Sym name, SymBind, SymKind,
ObjSymId obj_symbol_ex(ObjBuilder*, Sym name, SymBind, SymVis, SymKind,
ObjSecId section_id, u64 value, u64 size,
u64 common_align);
+/* Allocate a stable symbol id for data that may be discarded before emission.
+ * The returned symbol is tombstoned and not entered in the name index; callers
+ * must publish it with obj_symbol_define_live if the data is actually emitted. */
+ObjSymId obj_symbol_defer(ObjBuilder*, Sym name, SymBind, SymVis, SymKind,
+ u64 size);
ObjSymId obj_symbol_find(ObjBuilder*, Sym name);
/* obj_symbol_ex creates a symbol; obj_symbol_define fills in the
* (section_id, value, size) fields of an already-created symbol. The pair
@@ -455,6 +460,8 @@ ObjSymId obj_symbol_find(ObjBuilder*, Sym name);
* needed for a relocation, and defined later when its definition is emitted. */
void obj_symbol_define(ObjBuilder*, ObjSymId, ObjSecId section_id, u64 value,
u64 size);
+void obj_symbol_define_live(ObjBuilder*, ObjSymId, ObjSecId section_id,
+ u64 value, u64 size);
void obj_reloc(ObjBuilder*, ObjSecId section_id, u32 offset, RelocKind,
ObjSymId sym, i64 addend);
diff --git a/src/opt/pass_native_emit.c b/src/opt/pass_native_emit.c
@@ -120,8 +120,9 @@ static void emit_local_static_label_addr(NativeEmitCtx* e, MCLabel target,
static void emit_local_static_end(NativeEmitCtx* e, SrcLoc loc) {
if (!e->local_static_active) emit_panic(e, loc, "local static data inactive");
- obj_symbol_define(e->target->obj, e->local_static_sym, e->local_static_sec,
- e->local_static_base, e->local_static_size);
+ obj_symbol_define_live(e->target->obj, e->local_static_sym,
+ e->local_static_sec, e->local_static_base,
+ e->local_static_size);
e->local_static_active = 0;
e->local_static_sec = OBJ_SEC_NONE;
e->local_static_sym = OBJ_SYM_NONE;
diff --git a/test/opt/run.sh b/test/opt/run.sh
@@ -52,4 +52,69 @@ for opt in -O0 -O1; do
fi
done
+cat > "$WORK/dead_jt.c" <<'EOF'
+#include <kit/cg.h>
+int p(void) { return 0; }
+EOF
+"$KIT" cc -O1 -I "$ROOT/include" -c "$WORK/dead_jt.c" \
+ -o "$WORK/dead_jt.o" > "$WORK/dead_jt.cc.out" 2>&1
+"$KIT" nm "$WORK/dead_jt.o" > "$WORK/dead_jt.nm" 2>&1
+if grep -q '\.Lkit_jt' "$WORK/dead_jt.nm"; then
+ printf 'O1 deferred jump-table check FAILED: dead inline leaked .Lkit_jt:\n' >&2
+ sed 's/^/ | /' "$WORK/dead_jt.nm" >&2
+ exit 1
+fi
+
+cat > "$WORK/live_jt.c" <<'EOF'
+int p(int x) {
+ switch (x) {
+ case 0: return 3;
+ case 1: return 4;
+ case 2: return 5;
+ case 3: return 6;
+ case 4: return 7;
+ case 5: return 8;
+ case 6: return 9;
+ case 7: return 10;
+ default: return 11;
+ }
+}
+EOF
+"$KIT" cc -O1 -c "$WORK/live_jt.c" \
+ -o "$WORK/live_jt.o" > "$WORK/live_jt.cc.out" 2>&1
+"$KIT" nm "$WORK/live_jt.o" > "$WORK/live_jt.nm" 2>&1
+if grep -Eq '[[:space:]][uU][[:space:]]+\.Lkit_jt' "$WORK/live_jt.nm" ||
+ ! grep -Eq '[[:space:]][dDrR][[:space:]]+\.Lkit_jt' "$WORK/live_jt.nm"; then
+ printf 'O1 deferred jump-table check FAILED: live switch table not defined:\n' >&2
+ sed 's/^/ | /' "$WORK/live_jt.nm" >&2
+ exit 1
+fi
+
+cat > "$WORK/dead_ro.c" <<'EOF'
+static inline const char *q(void) { return "abc"; }
+int p(void) { return 0; }
+EOF
+"$KIT" cc -O1 -c "$WORK/dead_ro.c" \
+ -o "$WORK/dead_ro.o" > "$WORK/dead_ro.cc.out" 2>&1
+"$KIT" nm "$WORK/dead_ro.o" > "$WORK/dead_ro.nm" 2>&1
+if grep -q '\.Lkit_ro' "$WORK/dead_ro.nm"; then
+ printf 'O1 deferred const-data check FAILED: dead inline leaked .Lkit_ro:\n' >&2
+ sed 's/^/ | /' "$WORK/dead_ro.nm" >&2
+ exit 1
+fi
+
+cat > "$WORK/live_ro.c" <<'EOF'
+extern int sink(const char *);
+int p(void) { return sink("abc"); }
+EOF
+"$KIT" cc -O1 -c "$WORK/live_ro.c" \
+ -o "$WORK/live_ro.o" > "$WORK/live_ro.cc.out" 2>&1
+"$KIT" nm "$WORK/live_ro.o" > "$WORK/live_ro.nm" 2>&1
+if grep -Eq '[[:space:]][uU][[:space:]]+\.Lkit_ro' "$WORK/live_ro.nm" ||
+ ! grep -Eq '[[:space:]][dDrR][[:space:]]+\.Lkit_ro' "$WORK/live_ro.nm"; then
+ printf 'O1 deferred const-data check FAILED: live const data not defined:\n' >&2
+ sed 's/^/ | /' "$WORK/live_ro.nm" >&2
+ exit 1
+fi
+
printf 'tiny-inline: ok\n'
