Simple C Win32 Hello World program without preprocessor directives or library imports. Build with `cl *.c`.

hello_world.c

__pragma(comment(linker, "/entry:main"));
__pragma(comment(linker, "/subsystem:console"));

void *(*GetProcAddress)(void *module, const char *name);
void *(*LoadLibraryA)(const char *name);
void (*ExitProcess)(unsigned int return_code);
int (*MessageBoxA)(void *hWnd, const char *lpText, const char *lpCaption, unsigned int uType);

static inline void load_proc(void *lib, void *fn, char *name) {
	*(void **)fn = GetProcAddress(lib, name);
}

static inline void dynamic_link(void) {
	void *k32 = 0; // grab thread environment block to find loader data
	char *teb_pointer = (char *)__readgsqword(0x30);
	char *peb_pointer = *(char **)(teb_pointer + 0x60);
	char *ldr_data_pointer = *(char **)(peb_pointer + 0x18);
	char *entry_ptr = *(char **)(ldr_data_pointer + 0x20);

	while (*(void **)(entry_ptr + 0x30)) { // search for kernel32.dll
		unsigned short *libbuf = *(unsigned short **)(entry_ptr + 0x50);
		int liblen = *(unsigned short *)(entry_ptr + 0x48) / 2;
		int cmplen = sizeof(L"kernel32.dll") / 2;
		if (cmplen < liblen) cmplen = liblen;
		int i = 0;
		for (; i < cmplen; i += 1) {
			int ch1 = L"kernel32.dll"[i];
			int ch2 = libbuf[i];
			if (ch1 >= 'a' && ch1 <= 'z') ch1 &= ~0x20;
			if (ch2 >= 'a' && ch2 <= 'z') ch1 &= ~0x20;
			if (ch1 != ch2) break;
		}
		if (i == cmplen) {
			k32 = *(void **)(entry_ptr + 0x20);
			break;
		}
		entry_ptr = *(char **)entry_ptr;
	}
	if (!k32) __debugbreak();
	// parse kernel32.dll to grab function tables
	char *dos = (char *)k32;
	char *pe = dos + *(unsigned int *)(dos + 0x3C);
	char *export_table = dos + *(unsigned int *)(pe + 0x88);

	int number_of_name_pointers = *(unsigned int *)(export_table + 0x18);

	unsigned int *export_address_table = (unsigned int *)(dos + *(unsigned int *)(export_table + 0x1C));

	unsigned int *name_pointer_table = (unsigned int *)(dos + *(unsigned int *)(export_table + 0x20));

	unsigned short *ordinal_table = (unsigned short *)((char *)k32 + *(unsigned int *)(export_table + 0x24));

	// binary search for GetProcAddress
	int low = 0;
	int index = 0;
	int high = number_of_name_pointers - 1;
	int compare_result = 1;
	while (compare_result != 0) {
		if (compare_result > 0) {
			low = index;
		} else if (compare_result < 0) {
			high = index;
		}
		index = (high + low) / 2;
		const char *procedure_name = (const char *)((char *)k32 + name_pointer_table[index]);
		const char *getprocaddress_name = "GetProcAddress";
		for (;;) { // perform strcmp()
			if (*getprocaddress_name != *procedure_name) {
				compare_result = *(unsigned char *)getprocaddress_name - *(unsigned char *)procedure_name;
				break;
			}
			if (!*getprocaddress_name) {
				compare_result = 0;
				break;
			}
			getprocaddress_name += 1;
			procedure_name += 1;
		}
	}
	*(void **)&GetProcAddress = ((char *)k32 + export_address_table[ordinal_table[index]]);
	load_proc(k32, &LoadLibraryA, "LoadLibraryA");
	void *user32 = LoadLibraryA("user32.dll");
	load_proc(k32, &ExitProcess, "ExitProcess");
	load_proc(user32, &MessageBoxA, "MessageBoxA");
}

int main() {
	dynamic_link();
	MessageBoxA(0, "Hello, world!\n", "Message", 0);
	ExitProcess(0);
}

All credit goes to droidix: https://hero.handmade.network/forums/code-discussion/t/129-howto_-_building_without_import_libraries