kit

a.c (1153B)

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 /* &my_fn round-trips through a function pointer (cross-TU).
  *
  * a.c defines the IFUNC; b.c references it via &my_fn so the
  * address taken in b.c is observed across a TU boundary.  After
  * layout_iplt, the canonical IFUNC LinkSymbol is redirected to
  * the iplt stub; the per-input undef LinkSymbol in b.c had its
  * fields copied from the def by resolve_undefs (pre-redirect).
  * The propagation pass at the tail of layout_iplt re-syncs that
  * undef to the post-redirect (stub) vaddr, so the function
  * pointer in b.c carries the stub's address.
  *
  * Calling through the pointer goes through the stub: ADRP /
  * LDR / BR x16, hitting impl_a via the .igot.plt slot.  The
  * raw resolver address would have returned a function-pointer-
  * to-resolver that, when invoked, returns impl_a (a different
  * call shape we'd notice via test_main's return value). */
 
 extern int impl_a(void);
 extern int impl_b(void);
 extern int (*resolve(void))(void);
 
 int impl_a(void) { return 42; }
 int impl_b(void) { return 99; }
 
 int (*resolve(void))(void) {
   volatile int x = 1;
   return x ? impl_a : impl_b;
 }
 
 int my_fn(void) __attribute__((ifunc("resolve")));