path: root/examples/system/dynlink/main.c

/*
 * PSn00bSDK dynamic linker example (main executable)
 * (C) 2021 spicyjpeg - MPL licensed
 *
 * This example shows how to use the psxetc DL_*() APIs to obtain information
 * about the executable's symbols at runtime. This is accomplished by parsing a
 * symbol map file, which is generated at compile time by GCC's nm command and
 * included into the CD image. The symbol map lists all functions/variables in
 * the executable and their type, address and size. Currently only searching
 * for a symbol's address by its name (DL_GetSymbolByName()) is supported,
 * however this may be expanded in the future.
 *
 * Being able to introspect local symbols at runtime, in turn, allows us to use
 * the dl*() set of APIs to load, link and execute code from an external file
 * (compiled with the dll.ld linker script). A dynamically-loaded library can
 * reference and access any non-static function or variable within the main
 * executable (and the libraries the main executable has been compiled with);
 * the dynamic linker will automatically patch the DLL's code and resolve these
 * references so that they point to the addresses listed in the map file. DLLs
 * also have their own symbol tables, and any symbol in a DLL is accessible to
 * the main executable through dlsym().
 *
 * This example shows how DLLs can be loaded and unloaded at any time. Pressing
 * START will unload the current DLL and load an alternate one on-the-fly. A
 * custom resolver is also employed to tap into the DLL patching process and
 * override the printf() function referenced by the DLLs with a different
 * implementation, so the debug output from the DLLs can be redirected to the
 * on-screen overlay.
 *
 * Dynamic linking has plenty of practical applications. It can be e.g. used to
 * greatly reduce RAM usage by splitting off a large executable into a "common"
 * executable (containing SDK APIs as well as frequently-used symbols such as
 * rendering buffers) and many smaller DLLs, which can then be swapped in and
 * out depending on which functions are needed. It can also be useful to run
 * code that hasn't been compiled at the same time as the main executable, such
 * as plugins/mods/patches stored on a memory card.
 */

#include <sys/types.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <malloc.h>
#include <dlfcn.h>
#include <psxapi.h>
#include <psxetc.h>
#include <psxgte.h>
#include <psxgpu.h>
#include <psxpad.h>

#include "library/dll_common.h"

// List all SDK functions used by the DLLs in a dummy array to ensure GCC won't
// strip them. By default the linker removes all functions unused in the
// executable itself, but we (obviously) need them to be present for a DLL to
// call them. Placing this array in the .dummy section (as defined in the
// PSn00bSDK linker script) ensures it won't be stripped away until all
// functions are in place.
const void *const DO_NOT_STRIP[] __attribute__((section(".dummy"))) = {
	&rand,
	&InitGeom,
	&RotMatrix,
	&TransMatrix,
	&MulMatrix0
};

static const char *const DLL_FILENAMES[] = {
	"cdrom:CUBE.DLL;1",
	"cdrom:BALLS.DLL;1"
};

#define DLL_COUNT 2

void init_context(CONTEXT *ctx);
void display(CONTEXT *ctx);

/* Symbol overriding example */

static volatile uint32_t resolve_counter = 0;

// This function will override printf(), i.e. DLLs will use this instead of the
// "real" printf() present in the executable, thanks to the custom resolver
// defined below. We'll use this to redirect the DLL's output to the debug text
// window.
int dll_printf(const char *format, ...) {
	va_list args;
	va_start(args, format);

	char    buffer[256];
	int32_t return_value = vsprintf(buffer, format, args);
	va_end(args);

	FntPrint(-1, "DLL:  %s", buffer);
	//FntFlush(-1);

	return return_value;
}

// This function will be called by the linker for each undefined symbol
// (function or variable) in the DLL, and should return the address of the
// symbol so the dynamic linker can patch it in. The default resolver tries to
// find them in the currently loaded symbol map using DL_GetSymbolByName().
void *custom_resolver(DLL *dll, const char *name) {
	if (!strcmp(name, "printf")) {
		printf("Resolving printf() -> dll_printf() (#%d)\n", resolve_counter++);
		return &dll_printf;
	}

	printf("Resolving %s() (#%d)\n", name, resolve_counter++);

	// Custom resolvers should always fall back to the default behavior.
	return DL_GetSymbolByName(name);
}

/* Global variables and structs */

// Define a struct to store pointers to a DLL's functions into. This is not
// strictly required, however looking up symbols is a relatively slow operation
// and the pointers returned by dlsym() should be saved and reused as much as
// possible.
typedef struct {
	void (*init)(CONTEXT *);
	void (*render)(CONTEXT *, uint16_t buttons);
} DLL_API;

static DLL     *dll = 0;
static DLL_API dll_api;
static CONTEXT ctx;

/* Main */

#define SHOW_STATUS(...) { FntPrint(-1, __VA_ARGS__); FntFlush(-1); display(&ctx); }
#define SHOW_ERROR(...)  { SHOW_STATUS(__VA_ARGS__); while (1) __asm__("nop"); }

void load_dll(const char *filename) {
	if (dll)
		dlclose(dll);

	SHOW_STATUS("LOADING %s\n", filename);

	dll = dlopen(filename, RTLD_LAZY);
	if (!dll)
		SHOW_ERROR("FAILED TO LOAD %s\n%s\n", filename, dlerror());

	dll_api.init   = dlsym(dll, "init");
	dll_api.render = dlsym(dll, "render");

	printf("DLL init() @ %08x, render() @ %08x\n", dll_api.init, dll_api.render);

	// Unfortunately, due to how position-independent code works, function
	// pointers returned by dlsym() can't be called directly. We have to use
	// the DL_CALL() macro instead, which sets up register $t9 to ensure the
	// function can locate and reference the DLL's relocation table.
	DL_CALL(dll_api.init, &ctx);

}

int main(int argc, const char* argv[]) {
	// As DL_LoadSymbolMap() and dlopen() rely on BIOS file APIs, the BIOS CD
	// driver must be initialized by calling _InitCd() prior to loading the
	// symbol map (but after setting up the GPU, for some reason).
	init_context(&ctx);

	SHOW_STATUS("INITIALIZING CD\n");
	_InitCd();

	SHOW_STATUS("LOADING SYMBOL MAP\n");

	if (!DL_LoadSymbolMap("cdrom:MAIN.MAP;1"))
		SHOW_ERROR("FAILED TO LOAD SYMBOL MAP\n%s\n", dlerror());

	// Try to obtain a reference to a local function.
	void (*_display)() = DL_GetSymbolByName("display");
	if (!_display)
		SHOW_ERROR("FAILED TO LOOK UP LOCAL FUNCTION\n%s\n", dlerror());

	printf("Symbol map test, display() @ %08x\n", _display);

	// Set up controller polling.
	uint8_t pad_buff[2][34];
	InitPAD(pad_buff[0], 34, pad_buff[1], 34);
	StartPAD();
	ChangeClearPAD(0);

	// Set up the custom resolver and load the first DLL.
	DL_SetResolveCallback(&custom_resolver);
	load_dll(DLL_FILENAMES[0]);

	uint32_t dll_active   = 0;
	uint16_t last_buttons = 0xffff;

	while (1) {
		// Use the currently loaded DLL to render a frame.
		DL_CALL(dll_api.render, &ctx, last_buttons);

		FntPrint(-1, "MAIN: DLL ADDR=%08x SIZE=%d\n", dll->ptr, dll->size);
		FntPrint(-1, "MAIN: %d FUNCTIONS RESOLVED\n", resolve_counter);
		FntPrint(-1, "[START] LOAD NEXT DLL\n");
		FntFlush(-1);
		display(&ctx);

		// Check if a compatible controller is connected and if START has been
		// pressed (i.e. wasn't previously held down, but now is). If so,
		// switch the active DLL.
		PADTYPE *pad = (PADTYPE *) pad_buff[0];
		if (pad->stat)
			continue;
		if ((pad->type != 4) && (pad->type != 5) && (pad->type != 7))
			continue;

		if ((last_buttons & PAD_START) && !(pad->btn & PAD_START)) {
			dll_active++;
			dll_active %= DLL_COUNT;

			load_dll(DLL_FILENAMES[dll_active]);
		}

		last_buttons = pad->btn;
	}

	//dlclose(dll);
	//DL_UnloadSymbolMap();
	return 0;
}