Mocking with visibility=default

d-all.sh

gcc -m64 -O2 -o export_api main.c
nm -a export_api |grep ' [tT] ' |tee nm-t-0.txt

gcc -m64 -O2 -o export_api_1 -fvisibility=hidden main.c
nm -a export_api_1 |grep ' [tT] ' |tee nm-t-1.txt

g++ -m64 -O2 -o export_api_cxx main.c
nm -a export_api_cxx |grep ' [tT] ' |tee nm-t-2.txt

g++ -m64 -O2 -o export_api_cxx_1 -fvisibility=hidden main.c
nm -a export_api_cxx_1 |grep ' [tT] ' |tee nm-t-3.txt

g++ -m64 -O2 -o export_api_cxx_2 -fuse-ld=gold main.c
nm -a export_api_cxx_2 |grep ' [tT] ' |tee nm-t-4.txt

g++ -m64 -O2 -o export_api_cxx_3 -fuse-ld=gold -fvisibility=hidden main.c
nm -a export_api_cxx_3 |grep ' [tT] ' |tee nm-t-5.txt

echo "diff nm-t-0.txt nm-t-1.txt"
diff nm-t-0.txt nm-t-1.txt | c++filt
echo "diff nm-t-1.txt nm-t-2.txt"
diff nm-t-1.txt nm-t-2.txt | c++filt
echo "diff nm-t-2.txt nm-t-3.txt"
diff nm-t-2.txt nm-t-3.txt | c++filt
echo "diff nm-t-3.txt nm-t-4.txt"
diff nm-t-3.txt nm-t-4.txt | c++filt
echo "diff nm-t-4.txt nm-t-5.txt"
diff nm-t-4.txt nm-t-5.txt | c++filt

export-api.c

#ifdef __cplusplus
#  define EXTERN_C extern "C" 
#else
#  define EXTERN_C extern
#endif

#ifdef EXPORTING
#   ifdef _MSC_VER
#       define API __declspec(dllexport)
#   else
#       define API __attribute__((visibility("default")))
#   endif
#else
#   if MSVC
#       define API __declspec(dllimport)
#   else
#       define API __attribute__((visibility("default")))
#   endif
#endif

#define EXPORT_API EXTERN_C API

main.c

#include <stdio.h>

#define EXPORTING
#include "export-api.h"

// should be exported
EXTERN_C int api_a(void)
{
	return 1;
} 

// may be exported
int main(void)
{
	return 0;
}

// should be hidden
int unexported_api_a(void)
{
	return 2;
}

results.log

tsafin@M1BOOK6319:~/docs/examples/declspec-export$ ./do-all.sh
0000000000001140 T api_a
0000000000001080 t deregister_tm_clones
00000000000010f0 t __do_global_dtors_aux
0000000000003e20 t __do_global_dtors_aux_fini_array_entry
00000000000011c4 t .fini
00000000000011c4 T _fini
0000000000003e20 t .fini_array
0000000000001130 t frame_dummy
0000000000003e18 t __frame_dummy_init_array_entry
0000000000001000 t .init
0000000000001000 t _init
0000000000003e18 t .init_array
0000000000003e20 t __init_array_end
0000000000003e18 t __init_array_start
00000000000011c0 T __libc_csu_fini
0000000000001160 T __libc_csu_init
0000000000001040 T main
0000000000001020 t .plt
0000000000001030 t .plt.got
00000000000010b0 t register_tm_clones
0000000000001050 T _start
0000000000001040 t .text
0000000000001150 T unexported_api_a
0000000000001140 T api_a
0000000000001080 t deregister_tm_clones
00000000000010f0 t __do_global_dtors_aux
0000000000003e20 t __do_global_dtors_aux_fini_array_entry
00000000000011c4 t .fini
00000000000011c4 T _fini
0000000000003e20 t .fini_array
0000000000001130 t frame_dummy
0000000000003e18 t __frame_dummy_init_array_entry
0000000000001000 t .init
0000000000001000 t _init
0000000000003e18 t .init_array
0000000000003e20 t __init_array_end
0000000000003e18 t __init_array_start
00000000000011c0 T __libc_csu_fini
0000000000001160 T __libc_csu_init
0000000000001040 T main
0000000000001020 t .plt
0000000000001030 t .plt.got
00000000000010b0 t register_tm_clones
0000000000001050 T _start
0000000000001040 t .text
0000000000001150 T unexported_api_a
0000000000001140 T api_a
0000000000001080 t deregister_tm_clones
00000000000010f0 t __do_global_dtors_aux
0000000000003df0 t __do_global_dtors_aux_fini_array_entry
00000000000011c4 t .fini
00000000000011c4 T _fini
0000000000003df0 t .fini_array
0000000000001130 t frame_dummy
0000000000003de8 t __frame_dummy_init_array_entry
0000000000001000 t .init
0000000000001000 t _init
0000000000003de8 t .init_array
0000000000003df0 t __init_array_end
0000000000003de8 t __init_array_start
00000000000011c0 T __libc_csu_fini
0000000000001160 T __libc_csu_init
0000000000001040 T main
0000000000001020 t .plt
0000000000001030 t .plt.got
00000000000010b0 t register_tm_clones
0000000000001050 T _start
0000000000001040 t .text
0000000000001150 T _Z16unexported_api_av
0000000000001140 T api_a
0000000000001080 t deregister_tm_clones
00000000000010f0 t __do_global_dtors_aux
0000000000003df0 t __do_global_dtors_aux_fini_array_entry
00000000000011c4 t .fini
00000000000011c4 T _fini
0000000000003df0 t .fini_array
0000000000001130 t frame_dummy
0000000000003de8 t __frame_dummy_init_array_entry
0000000000001000 t .init
0000000000001000 t _init
0000000000003de8 t .init_array
0000000000003df0 t __init_array_end
0000000000003de8 t __init_array_start
00000000000011c0 T __libc_csu_fini
0000000000001160 T __libc_csu_init
0000000000001040 T main
0000000000001020 t .plt
0000000000001030 t .plt.got
00000000000010b0 t register_tm_clones
0000000000001050 T _start
0000000000001040 t .text
0000000000001150 T _Z16unexported_api_av
0000000000000630 T api_a
0000000000002018 T __bss_start
0000000000000570 t deregister_tm_clones
00000000000005e0 t __do_global_dtors_aux
0000000000001da0 t __do_global_dtors_aux_fini_array_entry
0000000000002018 T _edata
0000000000002019 T _end
00000000000006c4 t _fini
0000000000000620 t frame_dummy
0000000000001da8 t __frame_dummy_init_array_entry
00000000000004f0 t _init
0000000000001db0 t __init_array_end
0000000000001da8 t __init_array_start
00000000000006c0 T __libc_csu_fini
0000000000000660 T __libc_csu_init
0000000000000530 T main
00000000000005a0 t register_tm_clones
0000000000000540 T _start
0000000000000640 T _Z16unexported_api_av
0000000000000630 t api_a
0000000000002018 T __bss_start
0000000000000570 t deregister_tm_clones
00000000000005e0 t __do_global_dtors_aux
0000000000001da0 t __do_global_dtors_aux_fini_array_entry
0000000000002018 T _edata
0000000000002019 T _end
00000000000006c4 t _fini
0000000000000620 t frame_dummy
0000000000001da8 t __frame_dummy_init_array_entry
00000000000004f0 t _init
0000000000001db0 t __init_array_end
0000000000001da8 t __init_array_start
00000000000006c0 T __libc_csu_fini
0000000000000660 T __libc_csu_init
0000000000000530 t main
00000000000005a0 t register_tm_clones
0000000000000540 T _start
0000000000000640 t _Z16unexported_api_av
diff nm-t-0.txt nm-t-1.txt
diff nm-t-1.txt nm-t-2.txt
4c4
< 0000000000003e20 t __do_global_dtors_aux_fini_array_entry
---
> 0000000000003df0 t __do_global_dtors_aux_fini_array_entry
7c7
< 0000000000003e20 t .fini_array
---
> 0000000000003df0 t .fini_array
9c9
< 0000000000003e18 t __frame_dummy_init_array_entry
---
> 0000000000003de8 t __frame_dummy_init_array_entry
12,14c12,14
< 0000000000003e18 t .init_array
< 0000000000003e20 t __init_array_end
< 0000000000003e18 t __init_array_start
---
> 0000000000003de8 t .init_array
> 0000000000003df0 t __init_array_end
> 0000000000003de8 t __init_array_start
23c23
< 0000000000001150 T unexported_api_a
---
> 0000000000001150 T unexported_api_a()
diff nm-t-2.txt nm-t-3.txt
diff nm-t-3.txt nm-t-4.txt
1,23c1,19
< 0000000000001140 T api_a
< 0000000000001080 t deregister_tm_clones
< 00000000000010f0 t __do_global_dtors_aux
< 0000000000003df0 t __do_global_dtors_aux_fini_array_entry
< 00000000000011c4 t .fini
< 00000000000011c4 T _fini
< 0000000000003df0 t .fini_array
< 0000000000001130 t frame_dummy
< 0000000000003de8 t __frame_dummy_init_array_entry
< 0000000000001000 t .init
< 0000000000001000 t _init
< 0000000000003de8 t .init_array
< 0000000000003df0 t __init_array_end
< 0000000000003de8 t __init_array_start
< 00000000000011c0 T __libc_csu_fini
< 0000000000001160 T __libc_csu_init
< 0000000000001040 T main
< 0000000000001020 t .plt
< 0000000000001030 t .plt.got
< 00000000000010b0 t register_tm_clones
< 0000000000001050 T _start
< 0000000000001040 t .text
< 0000000000001150 T unexported_api_a()
---
> 0000000000000630 T api_a
> 0000000000002018 T __bss_start
> 0000000000000570 t deregister_tm_clones
> 00000000000005e0 t __do_global_dtors_aux
> 0000000000001da0 t __do_global_dtors_aux_fini_array_entry
> 0000000000002018 T _edata
> 0000000000002019 T _end
> 00000000000006c4 t _fini
> 0000000000000620 t frame_dummy
> 0000000000001da8 t __frame_dummy_init_array_entry
> 00000000000004f0 t _init
> 0000000000001db0 t __init_array_end
> 0000000000001da8 t __init_array_start
> 00000000000006c0 T __libc_csu_fini
> 0000000000000660 T __libc_csu_init
> 0000000000000530 T main
> 00000000000005a0 t register_tm_clones
> 0000000000000540 T _start
> 0000000000000640 T unexported_api_a()
diff nm-t-4.txt nm-t-5.txt
1c1
< 0000000000000630 T api_a
---
> 0000000000000630 t api_a
16c16
< 0000000000000530 T main
---
> 0000000000000530 t main
19c19
< 0000000000000640 T unexported_api_a()
---
> 0000000000000640 t unexported_api_a()