Meson build on macOS: undefined symbol treatment

[Emmanuel Blot]

Hi,

I’ve noticed that since meson builds have been enabled, on macOS, the 
build outcome with undefined symbols has changed:

- prior to meson introduction (v5.1.0):
  * referencing an undeclared symbol in source code led to a warning at 
compile stage
  * referencing an undeclared symbol at link stage led to a fatal build 
error (as usually expected)

- since meson introduction
  * same behavior at compile stage
  * however, the linker does silently generate an application - which 
fails at launch since the symbol is undefined.

Step to reproduce:

  from softmmu/main.c, replace for example call to qemu_init() with 
qemu_init2();

- v5.1.0:
  softmmu/main.c:48:5: warning: implicit declaration of function 
'qemu_init2' is invalid in C99 [-Wimplicit-function-declaration]
    qemu_init2(argc, argv, envp);
      LINK    riscv64-softmmu/qemu-system-riscv64
  Undefined symbols for architecture x86_64:
    "_qemu_init2", referenced from:
        _qemu_main in main.o
  ld: symbol(s) not found for architecture x86_64
  clang: error: linker command failed with exit code 1 (use -v to see 
invocation)
  make[1]: *** [qemu-system-riscv64] Error 1

- current master:
  softmmu/main.c:49:5: warning: implicit declaration of function 
'qemu_init2' is invalid in C99 [-Wimplicit-function-declaration]
    qemu_init2(argc, argv, envp);
    ^
  1 warning generated.
  [3/3] Linking target qemu-system-riscv64

 > riscv64-softmmu/qemu-system-riscv64
  dyld: lazy symbol binding failed: Symbol not found: _qemu_init2
    Referenced from: 
/Users/eblot/Sources/Git/github.com/QEMU/upstream/build/riscv64-softmmu/qemu-system-riscv64
    Expected in: flat namespace

    'riscv64-softmmu/qemu-system-ris…' terminated by signal SIGABRT 
(Abort)


This new behavior is likely to come from the linker flag:

   -Wl,-undefined,dynamic_lookup

I’m not sure whether it is a new feature or a bug, but if the former 
stands true, is there a way to disable this feature?


Thanks,
Emmanuel.