libmain.c

// loader code is taken from https://gist.github.com/apsun/1e144bf7639b22ff0097171fa0f8c6b1
// this is just for testing with lighthouse_console. For the driver, a shim library is a much better solution

#include <dlfcn.h>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
#include <stddef.h>

#include "redirect.h"
#include "common.h"

#include <hidapi.h>


#include "lh_hidapi.h"


/* Trampoline for the real main() */
static int (*main_orig)(int, char **, char **);

void* get_text_addr(){
    FILE* maps = fopen("/proc/self/maps", "r");
    if(!maps){
        printf("failed to open /proc/self/maps, can't get .text base address! exiting\n");
        exit(1);
    }
    char buf[256] = {0};
    fread(buf, sizeof(buf)-1, 1, maps);
    long text_base = strtol(buf, NULL, 16);
    //printf(".text base: 0x%lx\n", text_base);
    return (void*)text_base;
}

int main_hook(int argc, char** argv, char** c){
    printf("fake main called instead!\n");
    void* text_base = get_text_addr();
    lib_context* ctx = open_library("/proc/self/exe");
    
    set_text_base(ctx, text_base);
    setup_hooks(ctx);
    //redirect_function(orig_hid_init, lh_hid_init);

    main_orig(argc, argv, c);
    return 0;
}

/*
 * Wrapper for __libc_start_main() that replaces the real main
 * function with our hooked version.
 */
int __libc_start_main(
    int (*main)(int, char **, char **),
    int argc,
    char **argv,
    int (*init)(int, char **, char **),
    void (*fini)(void),
    void (*rtld_fini)(void),
    void *stack_end)
{
    /* Save the real main function address */
    main_orig = main;

    /* Find the real __libc_start_main()... */
    typeof(&__libc_start_main) orig = dlsym(RTLD_NEXT, "__libc_start_main");

    /* ... and call it with our custom main function */
    return orig(main_hook, argc, argv, init, fini, rtld_fini, stack_end);
}