BFM-decomp/cookbook/C0085.md

§75b — A body's preamble can carry #defines, not just externs; extraction lifts only the externs (Phase 29 SESSION-19, func_80165CA0 ×3 → fleet)

dedup_propagate's extract_unit walks BACKWARD from a definition collecting contiguous extern …; lines into the macro. It does not collect #defines — so a body matched with a file-scope macro in its preamble loses that macro when it is lifted into engine_core.h, and the shared body then compiles only where the source overlay's #define happens to be in scope above the splice point. This is the dedup_propagate counterpart of the family_remap._carry_macros gap Phase 27 closed.

The signature of this class is a LINK error, not a type error. undefined reference to 'SHB' — because an unexpanded SHB(x) is parsed as a call to an undeclared function (implicit int), which compiles cleanly and dies at link. Anything reporting conflicting types is a different class (§75/§75a). One grep tells them apart: is the name a #define or a symbol?

grep -rh '\b<name>\b' src --include=*.c --include=*.h | sort | uniq -c | sort -rn | head

If the top hit is #define <name>(x) …, it is this class.

Worked case. func_80165CA0 sat at ×3 for a phase. Its preamble in the source overlay is:

extern s32 D_8011D030;
extern s32 D_80126728;
#define SHB(x) __asm__ __volatile__("" : "=r"(x) : "0"(x))   /* <- NOT carried */
DEFINE_func_80165CA0()

The two externs were lifted; the #define between them was not. The other 132 overlays do define SHB — about 300 lines further down (ov_SC01_001: stub @4462, #define @4781), i.e. below the splice point. Pure ordering. And it explains the membership exactly: the 3 members are precisely the 3 files carrying the __volatile__ spelling of SHB — that define is the function's own preamble, still sitting above its instantiation.

Fix — the shared header OWNS the macro, under a distinct name:

#ifndef ENGINE_SHB
#define ENGINE_SHB(x) __asm__ __volatile__("" : "=r"(x) : "0"(x))
#endif

and rewrite the body's uses. Do not reuse the original name: the overlays define SHB themselves in two different spellings (volatile in 3 files, non-volatile in 132), and a shared #define SHB with a different replacement list is a hard redefinition error. A distinct name cannot collide with either. Pick the spelling the currently-banked members actually compile with (here volatile), not the one a stale body comment claims — then let the byte-gate confirm on those members before extending.

Generalises: any preamble construct that is not an extern — #define, a file-scope typedef, a static helper — is silently dropped by extraction and will cap the body's reach at whatever subset happens to supply it. When a group's reach is stuck at a suspiciously small number, diff the source overlay's preamble against what the macro actually carries.