build

Administrator@WIN-CUTEPBGVI8S /d/big_struct
$ cat main.c
#include <stdint.h>
#include <inttypes.h>
#include <stdio.h>

typedef struct TwoU64s {
    uint64_t one;
    uint64_t two;
} TwoU64s_t;

extern TwoU64s_t f(TwoU64s_t);

int main() {
    TwoU64s_t foo = { 42, 1337 };
    TwoU64s_t bar = f(foo);
    printf("foo: %"PRIu64" %"PRIu64"\n", foo.one, foo.two);
    printf("bar: %"PRIu64" %"PRIu64"\n", bar.one, bar.two);
    return 0;
}


Administrator@WIN-CUTEPBGVI8S /d/big_struct
$ cat fn.c
#include <stdint.h>

typedef struct TwoU64s {
        uint64_t one;
        uint64_t two;
} TwoU64s_t;

TwoU64s_t f(TwoU64s_t in) {
        TwoU64s_t out = { in.one + 10, in.two + 20 };
        return out;
}

Administrator@WIN-CUTEPBGVI8S /d/big_struct
$ clang -c fn.c

Administrator@WIN-CUTEPBGVI8S /d/big_struct
$ clang -o clang_out.exe main.c fn.o

Administrator@WIN-CUTEPBGVI8S /d/big_struct
$ ./clang_out.exe
foo: 42 1337
bar: 52 1357

Administrator@WIN-CUTEPBGVI8S /d/big_struct
$ gcc -o gcc_out.exe main.c fn.o

Administrator@WIN-CUTEPBGVI8S /d/big_struct
$ ./gcc_out.exe
foo: 5742371274752 8462087103658852352
bar: 5828270620672 180388626432

Administrator@WIN-CUTEPBGVI8S /d/big_struct
$ gcc -c fn.c

Administrator@WIN-CUTEPBGVI8S /d/big_struct
$ clang -o clang_out.exe main.c fn.o

Administrator@WIN-CUTEPBGVI8S /d/big_struct
$ ./clang_out.exe
foo: 180388626432 5742371274752
bar: 223342514314 5828270620672

Administrator@WIN-CUTEPBGVI8S /d/big_struct
$ gcc -o gcc_out.exe main.c fn.o

Administrator@WIN-CUTEPBGVI8S /d/big_struct
$ ./gcc_out.exe
foo: 42 1337
bar: 52 1357

Administrator@WIN-CUTEPBGVI8S /d/big_struct
$ gcc --version
gcc.exe (GCC) 4.8.1
Copyright (C) 2013 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.


Administrator@WIN-CUTEPBGVI8S /d/big_struct
$ clang --version
clang version 3.4 (trunk 194593) (llvm/trunk 194592)
Target: i686-pc-mingw32
Thread model: posix

Administrator@WIN-CUTEPBGVI8S /d/big_struct
$

fn.c

#include <stdint.h>

typedef struct TwoU64s {
    uint64_t one;
    uint64_t two;
} TwoU64s_t;

TwoU64s_t f(TwoU64s_t in) {
    TwoU64s_t out = { in.one + 10, in.two + 20 };
    return out;
}

main.c

#include <stdint.h>
#include <inttypes.h>
#include <stdio.h>

typedef struct TwoU64s {
    uint64_t one;
    uint64_t two;
} TwoU64s_t;

extern TwoU64s_t f(TwoU64s_t);

int main() {
    TwoU64s_t foo = { 42, 1337 };
    TwoU64s_t bar = f(foo);
    printf("foo: %"PRIu64" %"PRIu64"\n", foo.one, foo.two);
    printf("bar: %"PRIu64" %"PRIu64"\n", bar.one, bar.two);
    return 0;
}