C: sqlite runtime undefined symbol sqlite3MemSetDefault

• Type: bug (C frontend / runtime / symbol resolution) — Track C
• Status: DONE (2026-06-27)
• Owner: Track C+A
• Found / Opened: 2026-06-27, M5 sqlite bring-up ([[feature-c-desktop-lua-sqlite-path]]), immediately after the function-pointer-array global wall ([[bug-c-null-pointer-literal-call-arg-sqlite]]) was cleared.

Symptom

sqlite3.c now fully compiles and links; a small driver

int main(void){
  sqlite3 *db;
  int rc = sqlite3_open(":memory:", &db);
  if (rc==0) sqlite3_close(db);
  return rc;
}

builds to an executable but faults at run time before producing output:

symbol lookup error: ...: undefined symbol: sqlite3MemSetDefault

Notes

sqlite3MemSetDefault is a real sqlite memory-subsystem routine, selected at build time by the SQLITE_SYSTEM_MALLOC / SQLITE_MEMDEBUG / MEMSYS* configuration. Under the amalgamation's default config one of the mem*.c implementations defines it; the symbol is reachable (referenced by sqlite3MallocInit) but its definition is apparently behind a preprocessor branch the cfront preprocessor is dropping, so the linker emits an undefined extern instead of binding it internally.

Likely a #ifdef/#if defined(...) (or a SQLITE_DEFAULT_MEMSTATUS-gated) block whose definition is not being emitted — investigate which mem1/mem2/... arm should be active and whether the cfront preprocessor evaluates that condition the same way the C amalgamation expects. This is the next sqlite runtime wall; the compile/lowering path is clean.

Acceptance

• sqlite3MemSetDefault (and any sibling memory-subsystem routines exposed the same way) resolve internally; no undefined-symbol fault at startup.
• sqlite3_open(":memory:") + sqlite3_close runs to completion.

Resolution (2026-06-27, Track C+A)

Not a symbol-resolution bug — a preprocessor arithmetic bug. sqlite selects its allocator with:

#if defined(SQLITE_SYSTEM_MALLOC) + defined(SQLITE_WIN32_MALLOC) \
  + defined(SQLITE_ZERO_MALLOC) + defined(SQLITE_MEMDEBUG) == 0
# define SQLITE_SYSTEM_MALLOC 1
#endif

The cfront #if evaluator (cpreproc.inc) had no additive / multiplicative / shift / bitwise levels at all — its chain was Or → And → Compare → Unary → Atom. So a + b, a & b, a << b silently dropped everything after the first operand: 0 + 5 evaluated to 0 (the + 5 was never consumed; 5 + 0 only "worked" because the left operand 5 is already truthy). The defined()+…==0 sum therefore never fired, SQLITE_SYSTEM_MALLOC stayed undefined, the mem1 allocator block (#ifdef SQLITE_SYSTEM_MALLOC) — which defines sqlite3MemSetDefault — was excluded, and the linker emitted an undefined extern.

Fix: implemented the full C #if constant-expression precedence hierarchy in cpreproc.inc — unary (! ~ - +) → * / % → + - → << >> → < <= > >= → == != → & → ^ → | → && → ||, each left-associative, with two-char guards so &/&&, |/||, </<<, >/>> don't collide. Self-host byte-identical (C-only code path); make test green. Regression test/cpreproc_if_arith_b110.c (exit 42).

sqlite3MemSetDefault now resolves. sqlite3_open(":memory:") advances to the next wall — undefined symbol: fabs (libm math functions aren't getting a DT_NEEDED), filed as [[bug-c-sqlite-math-libm-not-linked]].