QEMU for architecture-switching chroot (eg: initial RPi setup)

qemu-arch-cpu.c

// based on: https://www.gentoo.org/proj/en/base/embedded/handbook/?part=1&chap=5
// build as: gcc -static qemu-arch-cpu.c -O3 -s -o /usr/bin/qemu-arch-cpu
// use like: ln -s /usr/bin/qemu-arch-cpu /usr/bin/qemu-arm-arm1176

#include <malloc.h>
#include <string.h>
#include <unistd.h>

char** parse_tuple(char* tuple) {
    int pos = 0;
    char** result = malloc(2 * sizeof(char*));

    while (tuple[pos] != '-' && tuple[pos] != '\0') ++pos;
    if (tuple[pos] == '\0') return NULL; else pos += 1;
    result[0] = tuple + pos;

    while (tuple[pos] != '-' && tuple[pos] != '\0') ++pos;
    if (tuple[pos] == '\0') return NULL; else tuple[pos] = '\0';
    result[1] = tuple + pos + 1;

    return result;
}

char* create_name(char* arch) {
    const char* qemu = "/usr/bin/qemu-";
    int len = strlen(qemu) + strlen(arch) + 1;

    char* result = (char*)malloc(len * sizeof(char));
    if (result == NULL) return result;

    sprintf(result, "%s%s", qemu, arch);
    return result;
}

int main(int argc, char** argv, char** envp) {
    char** newargv = NULL;
    char** tuple = NULL;

    newargv = malloc((argc + 3) * sizeof(char*));
    if (newargv == NULL) return -1;

    tuple = parse_tuple(argv[0]);
    if (tuple == NULL) return -2;

    newargv[0] = create_name(tuple[0]);
    if (newargv[0] == NULL) return -1;

    newargv[1] = "-cpu";
    newargv[2] = tuple[1];

    for (i = 0; i < argc - 1; ++i)
        newargv[i + 3] = argv[i + 1];
    newargv[argc + 2] = NULL;

    return execve(newargv[0], newargv, envp);
}