kit

commit fe54567af671bb0d6c2a0d5e31ab35c47dd67e18
parent 9bd45ea57728ff2c56b443b35beb4f1db8df27f2
Author: Ryan Sepassi <rsepassi@gmail.com>
Date:   Sat, 13 Jun 2026 11:36:03 -0700

perf(obj): single-pass symtab counts + direct strtab write at objwrite (C4)

(cherry picked from commit 30b390acbcf31ecc51aa39f8b5d4f342fd529f0a)

Diffstat:
M
src/obj/elf/emit.c
 | 
20
++++++--------------
M
src/obj/macho/emit.c
 | 
61
+++++++++++++------------------------------------------------

2 files changed, 19 insertions(+), 62 deletions(-)
diff --git a/src/obj/elf/emit.c b/src/obj/elf/emit.c
@@ -312,7 +312,11 @@ void emit_elf(Compiler* c, ObjBuilder* ob, Writer* w) {
   /* Map obj symbol id -> elf symbol index. */
   u32* sym_to_elf = arena_zarray(c->scratch, u32, nobjsym + 2);
 
-  /* Two passes over obj symbols: locals, then globals/weak. */
+  /* Two passes over obj symbols: locals, then globals/weak.
+   * sh_info on .symtab is the index of the first non-local symbol;
+   * since pass 0 emits exactly the LOCAL non-removed symbols, count
+   * them inline (seeded with 1 for STN_UNDEF) instead of re-walking. */
+  u32 nlocals = 1;
   for (int pass = 0; pass < 2; ++pass) {
     ObjSymIter* it = obj_symiter_new(ob);
     ObjSymEntry e;
@@ -332,24 +336,12 @@ void emit_elf(Compiler* c, ObjBuilder* ob, Writer* w) {
       WRITE_SYM(nsyms, nameoff, info, other, shndx, value, s->size);
       sym_to_elf[e.id] = nsyms;
       nsyms++;
+      if (pass == 0) ++nlocals;
     }
     obj_symiter_free(it);
   }
 #undef WRITE_SYM
 
-  /* sh_info on .symtab is the index of the first non-local symbol.
-   * Locals = 1 (STN_UNDEF) + count of input-side LOCAL obj symbols. */
-  u32 nlocals = 1;
-  {
-    ObjSymIter* it = obj_symiter_new(ob);
-    ObjSymEntry e;
-    while (obj_symiter_next(it, &e)) {
-      if (e.sym->removed) continue;
-      if (e.sym->bind == SB_LOCAL) ++nlocals;
-    }
-    obj_symiter_free(it);
-  }
-
   /* Append .symtab + .strtab + .shstrtab planning records.
    * sh_link/sh_info for .symtab and .rela.* are filled in once we know
    * each section's elf index. */
diff --git a/src/obj/macho/emit.c b/src/obj/macho/emit.c
@@ -391,7 +391,10 @@ void emit_macho(Compiler* c, ObjBuilder* ob, Writer* w) {
   }
 
   /* Emit in three passes so n_type/sect ordering matches LC_DYSYMTAB
-   * (locals, then extdefs, then undefs). */
+   * (locals, then extdefs, then undefs).  The pass index IS the on-disk
+   * class, so the per-pass emit counts ARE the LC_DYSYMTAB partition
+   * sizes — count them inline instead of re-walking the symbols. */
+  u32 nlocals = 0, nextdefs = 0, nundefs = 0;
   for (int pass = 0; pass < 3; ++pass) {
     ObjSymIter* it = obj_symiter_new(ob);
     ObjSymEntry e;
@@ -482,48 +485,12 @@ void emit_macho(Compiler* c, ObjBuilder* ob, Writer* w) {
 
       sym_obj_to_macho[e.id] = nmsyms + 1; /* 1-based index, 0 = none. */
       nmsyms++;
-    }
-    obj_symiter_free(it);
-  }
-
-  u32 nlocals = 0, nextdefs = 0, nundefs = 0;
-  for (u32 i = 0; i < nmsyms; ++i) {
-    u8 t = msyms[i].n_type;
-    u8 ext = (t & N_EXT) != 0;
-    u8 typ = (u8)(t & N_TYPE);
-    if (typ == N_UNDF && ext) {
-      /* Could be undef or common — common has nonzero n_value. */
-      if (msyms[i].n_value != 0)
-        ++nextdefs; /* common is conventionally extdef-shaped */
-      else
-        ++nundefs;
-    } else if (ext) {
-      ++nextdefs;
-    } else {
-      ++nlocals;
-    }
-  }
-  /* Re-derive without the common fudge by counting partition pass: we
-   * already wrote them in (locals,extdefs,undefs) order, so the prefix
-   * counts are just the per-pass counts. Mirror the spurious-UNDEF
-   * prune from the emit loop above so the LC_DYSYMTAB index counts
-   * line up with the symbols we actually wrote. */
-  nlocals = 0;
-  nextdefs = 0;
-  nundefs = 0;
-  {
-    ObjSymIter* it = obj_symiter_new(ob);
-    ObjSymEntry e;
-    while (obj_symiter_next(it, &e)) {
-      const ObjSym* s = e.sym;
-      if (s->removed) continue;
-      int undef = sym_is_undef(s);
-      if (undef)
-        ++nundefs;
-      else if (sym_is_extdef(s))
+      if (pass == 0)
+        ++nlocals;
+      else if (pass == 1)
         ++nextdefs;
       else
-        ++nlocals;
+        ++nundefs;
     }
     obj_symiter_free(it);
   }
@@ -849,12 +816,10 @@ void emit_macho(Compiler* c, ObjBuilder* ob, Writer* w) {
     kit_writer_write(w, entry, MACHO_NLIST64_SIZE);
   }
 
-  /* strtab */
-  {
-    u8* flat = (u8*)arena_alloc(c->scratch, strtab_size ? strtab_size : 1, 1);
-    if (strtab_size) memcpy(flat, obj_strtab_data(&strtab), strtab_size);
-    kit_writer_seek(w, stroff);
-    kit_writer_write(w, flat, strtab_size);
-  }
+  /* strtab — kit_writer_write consumes synchronously and nothing
+   * appends to the strtab after this point, so write its contiguous
+   * buffer directly (no flatten copy) and free it afterwards. */
+  kit_writer_seek(w, stroff);
+  if (strtab_size) kit_writer_write(w, obj_strtab_data(&strtab), strtab_size);
   obj_strtab_fini(&strtab);
 }