a.cpp

#include "a.h"

void a() {
  data = 42;
}

a.h

extern int data;

void a();

b.cpp

#include <stdio.h>

#include "a.h"

int data = 0;

struct B {
  B() {
    printf("B(), data=%d\n", data);
  }
  ~B() {
    printf("~B(), data=%d\n", data);
  }
};

int main() {
  B b;
  a();
}

output.wat

;;
;; relevant output from running
;;
;; ./emcc a.cpp b.cpp -O1 --profiling -fwasm-exceptions -s ENVIRONMENT=shell
;;

(func $a\28\29
  (i32.store offset=1680
   (i32.const 0)
   (i32.const 42)
  )
 )
 (func $__original_main (result i32)
  (local $0 i32)
  (global.set $__stack_pointer
   (local.tee $0
    (i32.sub
     (global.get $__stack_pointer)
     (i32.const 48)
    )
   )
  )
  (i32.store offset=32
   (local.get $0)
   (i32.load offset=1680
    (i32.const 0)
   )
  )
  (drop
   (call $iprintf
    (i32.const 1042)
    (i32.add
     (local.get $0)
     (i32.const 32)
    )
   )
  )
  (try $label$3 ;; unnecessary try-catch
   (do
    (call $a\28\29)
   )
   (catch_all
    (global.set $__stack_pointer
     (local.get $0)
    )
    (i32.store offset=16
     (local.get $0)
     (i32.load offset=1680
      (i32.const 0)
     )
    )
    (drop
     (call $iprintf
      (i32.const 1041)
      (i32.add
       (local.get $0)
       (i32.const 16)
      )
     )
    )
    (rethrow $label$3)
   )
  )
  (i32.store
   (local.get $0)
   (i32.load offset=1680
    (i32.const 0)
   )
  )
  (drop
   (call $iprintf
    (i32.const 1041)
    (local.get $0)
   )
  )
  (global.set $__stack_pointer
   (i32.add
    (local.get $0)
    (i32.const 48)
   )
  )
  (i32.const 0)
 )