loader_main.cpp

/* SPDX-License-Identifier: MIT */
/*
 * MIT License
 *
 * Copyright (c) 2018 Mikhail Ilyin
 * Copyright (c) 2025 Lukas Straub
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#include "loader.h"
#include "trampo.h"
#include "intercept.h"
#include "features.h"
#include "../libs/musl/src/include/features.h"
#include "../libs/musl/src/internal/libc.h"
#include "debug.h"

#include <string.h>
#include <unistd.h>
#include <sys/prctl.h>

extern char** environ;
int main(int argc, char** argv, char** envp) {
    unsigned long* sp = (unsigned long*)argv;
    sp--;
    unsigned long* auxv;
    void* after_auxv;
    char** p;
    struct LoaderInfo info;

    for (p = envp; *p++;)
        ;
    auxv = (unsigned long*)p;

    // todo: allow fd for execveat
    char* exe = getenv("LOADER_RECURSE");
    int recursing = exe != NULL;
    if (!recursing) {
        if (argc < 2) {
            exit_error("no input file");
        }
        exe = argv[1];
    }

    intercept_init(recursing, exe, auxv);

    load_file(&info, exe);

    after_auxv = patch_auxv(auxv, &info, exe);

    char* basename = strrchr(exe, '/');
    if (!basename) {
        basename = exe;
    } else {
        basename += 1;
    }
    int ret = prctl(PR_SET_NAME, (uintptr_t)basename);
    if (ret < 0) {
        abort();
    }

    if (recursing) {
        /* Shift av after modifying the environment */
        unsetenv("LOADER_RECURSE");
        memcpy(auxv - 1, auxv, (unsigned long)after_auxv - (unsigned long)auxv);
        libc.auxv--;
    } else {
        /* Shift argv, env and av. */
        memcpy(&argv[0], &argv[1],
               (unsigned long)after_auxv - (unsigned long)&argv[1]);
        environ--;
        libc.auxv--;
        /* SP points to argc. */
        (*sp)--;
    }

    z_trampo((void (*)(void))(info.elf_interp ? info.entry[Z_INTERP]
                                              : info.entry[Z_PROG]),
             sp, nullptr);
    /* Should not reach. */
    exit(0);
}