initSystem.c

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#include <sys/iosupport.h>
#include <string.h>
#include <3ds.h>

// System globals we define here
int __system_argc;
char** __system_argv;
void (*__system_retAddr)(void);
u32 __linear_heap;

// Data from _prm structure
extern void* __service_ptr; // used to detect if we're run from a homebrew launcher
extern u32 __heap_size, __linear_heap_size;
extern const char* __system_arglist;

// newlib definitions we need
void __libc_init_array(void);
void __libc_fini_array(void);
extern char* fake_heap_start;
extern char* fake_heap_end;

static void initArgv();
static u32 heapBase;

void __destroy_handle_list(void);

void __attribute__((noreturn)) __ctru_exit(int rc)
{
    // Run the global destructors
    __libc_fini_array();

    // TODO: APT exit goes here

    // Unmap the linear heap
    svcControlMemory(&__linear_heap, __linear_heap, 0x0, __linear_heap_size, MEMOP_FREE, 0x0);

    // Unmap the application heap
    svcControlMemory(&heapBase, heapBase, 0x0, __heap_size, MEMOP_FREE, 0x0);

    // Close some handles
    __destroy_handle_list();

    // Jump to the loader if it provided a callback
    if (__system_retAddr)
        __system_retAddr();

    // Since above did not jump, end this process
    svcExitProcess();
}

void initSystem(void (*retAddr)(void))
{
    // Register newlib exit() syscall
    __syscalls.exit = __ctru_exit;
    __system_retAddr = __service_ptr ? retAddr : NULL;

    // Allocate the application heap
    heapBase = 0x08000000;
    svcControlMemory(&heapBase, heapBase, 0x0, __heap_size, MEMOP_ALLOC, 0x3);

    // Allocate the linear heap
    svcControlMemory(&__linear_heap, 0x0, 0x0, __linear_heap_size, MEMOP_ALLOC_LINEAR, 0x3);

    // Set up newlib heap
    fake_heap_start = (char*)heapBase;
    fake_heap_end = fake_heap_start + __heap_size;

    // Build argc/argv if present
    initArgv();

    // TODO: APT init goes here

    // Run the global constructors
    __libc_init_array();
}

void initArgv()
{
    int i;
    const char* temp = __system_arglist;

    // Check if the argument list is present
    if (!temp)
        return;

    // Retrieve argc
    __system_argc = *(u32*)temp;
    temp += sizeof(u32);

    // Find the end of the argument data
    for (i = 0; i < __system_argc; i ++)
    {
        for (; *temp; temp ++);
        temp ++;
    }

    // Reserve heap memory for argv data
    u32 argSize = temp - __system_arglist - sizeof(u32);
    __system_argv = (char**)fake_heap_start;
    fake_heap_start += sizeof(char**)*(__system_argc + 1);
    char* argCopy = fake_heap_start;
    fake_heap_start += argSize;

    // Fill argv array
    memcpy(argCopy, &__system_arglist[4], argSize);
    temp = argCopy;
    for (i = 0; i < __system_argc; i ++)
    {
        __system_argv[i] = (char*)temp;
        for (; *temp; temp ++);
        temp ++;
    }
    __system_argv[__system_argc] = NULL;
}