bootimg.cpp

#include <functional>
#include <memory>

#include <libfdt.h>
#include <mincrypt/sha.h>
#include <mincrypt/sha256.h>
#include <base.hpp>

#include "bootimg.hpp"
#include "magiskboot.hpp"
#include "compress.hpp"

#ifdef SVB_WIN32
#define off64_t off_t
#define lseek64 lseek
#define ftruncate64 ftruncate
#endif

using namespace std;

uint32_t dyn_img_hdr::j32 = 0;
uint64_t dyn_img_hdr::j64 = 0;

#define PADDING 15

static void decompress(format_t type, int fd, const void *in, size_t size) {
    auto ptr = get_decoder(type, make_unique<fd_stream>(fd));
    ptr->write(in, size, true);
}

static off_t compress(format_t type, int fd, const void *in, size_t size) {
    auto prev = lseek(fd, 0, SEEK_CUR);
    {
        auto strm = get_encoder(type, make_unique<fd_stream>(fd));
        strm->write(in, size, true);
    }
    auto now = lseek(fd, 0, SEEK_CUR);
    return now - prev;
}

static void dump(const void *buf, size_t size, const char *filename) {
    if (size == 0)
        return;
    int fd = creat(filename, 0644);
    xwrite(fd, buf, size);
    close(fd);
}

static size_t restore(int fd, const char *filename) {
    int ifd = xopen(filename, O_RDONLY);
    size_t size = lseek(ifd, 0, SEEK_END);
    lseek(ifd, 0, SEEK_SET);
    xsendfile(fd, ifd, nullptr, size);
    close(ifd);
    return size;
}

void dyn_img_hdr::print() {
    uint32_t ver = header_version();
    fprintf(stderr, "%-*s [%u]\n", PADDING, "HEADER_VER", ver);
    if (!is_vendor)
        fprintf(stderr, "%-*s [%u]\n", PADDING, "KERNEL_SZ", kernel_size());
    fprintf(stderr, "%-*s [%u]\n", PADDING, "RAMDISK_SZ", ramdisk_size());
    if (ver < 3)
        fprintf(stderr, "%-*s [%u]\n", PADDING, "SECOND_SZ", second_size());
    if (ver == 0)
        fprintf(stderr, "%-*s [%u]\n", PADDING, "EXTRA_SZ", extra_size());
    if (ver == 1 || ver == 2)
        fprintf(stderr, "%-*s [%u]\n", PADDING, "RECOV_DTBO_SZ", recovery_dtbo_size());
    if (ver == 2 || is_vendor)
        fprintf(stderr, "%-*s [%u]\n", PADDING, "DTB_SZ", dtb_size());

    if (uint32_t os_ver = os_version()) {
        int a,b,c,y,m = 0;
        int version = os_ver >> 11;
        int patch_level = os_ver & 0x7ff;

        a = (version >> 14) & 0x7f;
        b = (version >> 7) & 0x7f;
        c = version & 0x7f;
        fprintf(stderr, "%-*s [%d.%d.%d]\n", PADDING, "OS_VERSION", a, b, c);

        y = (patch_level >> 4) + 2000;
        m = patch_level & 0xf;
        fprintf(stderr, "%-*s [%d-%02d]\n", PADDING, "OS_PATCH_LEVEL", y, m);
    }

    fprintf(stderr, "%-*s [%u]\n", PADDING, "PAGESIZE", page_size());
    if (char *n = name()) {
        fprintf(stderr, "%-*s [%s]\n", PADDING, "NAME", n);
    }
    fprintf(stderr, "%-*s [%.*s%.*s]\n", PADDING, "CMDLINE",
            BOOT_ARGS_SIZE, cmdline(), BOOT_EXTRA_ARGS_SIZE, extra_cmdline());
    if (char *checksum = id()) {
        fprintf(stderr, "%-*s [", PADDING, "CHECKSUM");
        for (int i = 0; i < SHA256_DIGEST_SIZE; ++i)
            fprintf(stderr, "%02hhx", checksum[i]);
        fprintf(stderr, "]\n");
    }
}

void dyn_img_hdr::dump_hdr_file() {
    FILE *fp = xfopen(HEADER_FILE, "w");
    if (name())
        fprintf(fp, "name=%s\n", name());
    fprintf(fp, "cmdline=%.*s%.*s\n", BOOT_ARGS_SIZE, cmdline(), BOOT_EXTRA_ARGS_SIZE, extra_cmdline());
    uint32_t ver = os_version();
    if (ver) {
        int a, b, c, y, m;
        int version, patch_level;
        version = ver >> 11;
        patch_level = ver & 0x7ff;

        a = (version >> 14) & 0x7f;
        b = (version >> 7) & 0x7f;
        c = version & 0x7f;
        fprintf(fp, "os_version=%d.%d.%d\n", a, b, c);

        y = (patch_level >> 4) + 2000;
        m = patch_level & 0xf;
        fprintf(fp, "os_patch_level=%d-%02d\n", y, m);
    }
    fclose(fp);
}

void dyn_img_hdr::load_hdr_file() {
    parse_prop_file(HEADER_FILE, [=](string_view key, string_view value) -> bool {
        if (key == "name" && name()) {
            memset(name(), 0, 16);
            memcpy(name(), value.data(), value.length() > 15 ? 15 : value.length());
        } else if (key == "cmdline") {
            memset(cmdline(), 0, BOOT_ARGS_SIZE);
            memset(extra_cmdline(), 0, BOOT_EXTRA_ARGS_SIZE);
            if (value.length() > BOOT_ARGS_SIZE) {
                memcpy(cmdline(), value.data(), BOOT_ARGS_SIZE);
                auto len = std::min(value.length() - BOOT_ARGS_SIZE, (size_t) BOOT_EXTRA_ARGS_SIZE);
                memcpy(extra_cmdline(), &value[BOOT_ARGS_SIZE], len);
            } else {
                memcpy(cmdline(), value.data(), value.length());
            }
        } else if (key == "os_version") {
            int patch_level = os_version() & 0x7ff;
            int a, b, c;
            sscanf(value.data(), "%d.%d.%d", &a, &b, &c);
            os_version() = (((a << 14) | (b << 7) | c) << 11) | patch_level;
        } else if (key == "os_patch_level") {
            int os_ver = os_version() >> 11;
            int y, m;
            sscanf(value.data(), "%d-%d", &y, &m);
            y -= 2000;
            os_version() = (os_ver << 11) | (y << 4) | m;
        }
        return true;
    });
}

boot_img::boot_img(const char *image) : map(image) {
    fprintf(stderr, "Parsing image: [%s]\n", image);
    for (const uint8_t *addr = map.buf; addr < map.buf + map.sz; ++addr) {
        format_t fmt = check_fmt(addr, map.sz);
        switch (fmt) {
        case CHROMEOS:
            // chromeos require external signing
            flags[CHROMEOS_FLAG] = true;
            addr += 65535;
            break;
        case DHTB:
            flags[DHTB_FLAG] = true;
            flags[SEANDROID_FLAG] = true;
            fprintf(stderr, "DHTB_HDR\n");
            addr += sizeof(dhtb_hdr) - 1;
            break;
        case BLOB_FMT:
            flags[BLOB_FLAG] = true;
            fprintf(stderr, "TEGRA_BLOB\n");
            addr += sizeof(blob_hdr) - 1;
            break;
        case AOSP:
        case AOSP_VENDOR:
            parse_image(addr, fmt);
            return;
        default:
            break;
        }
    }
    exit(1);
}

boot_img::~boot_img() {
    delete hdr;
}

static int find_dtb_offset(const uint8_t *buf, unsigned sz) {
    const uint8_t * const end = buf + sz;

    for (auto curr = buf; curr < end; curr += sizeof(fdt_header)) {
        curr = static_cast<uint8_t*>(memmem(curr, end - curr, DTB_MAGIC, sizeof(fdt32_t)));
        if (curr == nullptr)
            return -1;

        auto fdt_hdr = reinterpret_cast<const fdt_header *>(curr);

        // Check that fdt_header.totalsize does not overflow kernel image size
        uint32_t totalsize = fdt32_to_cpu(fdt_hdr->totalsize);
        if (totalsize > end - curr)
            continue;

        // Check that fdt_header.off_dt_struct does not overflow kernel image size
        uint32_t off_dt_struct = fdt32_to_cpu(fdt_hdr->off_dt_struct);
        if (off_dt_struct > end - curr)
            continue;

        // Check that fdt_node_header.tag of first node is FDT_BEGIN_NODE
        auto fdt_node_hdr = reinterpret_cast<const fdt_node_header *>(curr + off_dt_struct);
        if (fdt32_to_cpu(fdt_node_hdr->tag) != FDT_BEGIN_NODE)
            continue;

        return curr - buf;
    }
    return -1;
}

static format_t check_fmt_lg(const uint8_t *buf, unsigned sz) {
    format_t fmt = check_fmt(buf, sz);
    if (fmt == LZ4_LEGACY) {
        // We need to check if it is LZ4_LG
        uint32_t off = 4;
        uint32_t block_sz;
        while (off + sizeof(block_sz) <= sz) {
            memcpy(&block_sz, buf + off, sizeof(block_sz));
            off += sizeof(block_sz);
            if (off + block_sz > sz)
                return LZ4_LG;
            off += block_sz;
        }
    }
    return fmt;
}

#define CMD_MATCH(s) BUFFER_MATCH(h->cmdline, s)

dyn_img_hdr *boot_img::create_hdr(const uint8_t *addr, format_t type) {
    if (type == AOSP_VENDOR) {
        fprintf(stderr, "VENDOR_BOOT_HDR\n");
        auto h = reinterpret_cast<const boot_img_hdr_vnd_v3*>(addr);
        hdr_addr = addr;
        switch (h->header_version) {
        case 4:
            return new dyn_img_vnd_v4(addr);
        default:
            return new dyn_img_vnd_v3(addr);
        }
    }

    auto h = reinterpret_cast<const boot_img_hdr_v0*>(addr);

    if (h->page_size >= 0x02000000) {
        fprintf(stderr, "PXA_BOOT_HDR\n");
        hdr_addr = addr;
        return new dyn_img_pxa(addr);
    }

    auto make_hdr = [](const uint8_t *ptr) -> dyn_img_hdr * {
        auto h = reinterpret_cast<const boot_img_hdr_v0*>(ptr);
        switch (h->header_version) {
        case 1:
            return new dyn_img_v1(ptr);
        case 2:
            return new dyn_img_v2(ptr);
        case 3:
            return new dyn_img_v3(ptr);
        case 4:
            return new dyn_img_v4(ptr);
        default:
            return new dyn_img_v0(ptr);
        }
    };

    // For NOOKHD and ACCLAIM, the entire boot image is shifted by a fixed offset.
    // For AMONET, only the header is internally shifted by a fixed offset.

    if (BUFFER_CONTAIN(addr, AMONET_MICROLOADER_SZ, AMONET_MICROLOADER_MAGIC) &&
        BUFFER_MATCH(addr + AMONET_MICROLOADER_SZ, BOOT_MAGIC)) {
        flags[AMONET_FLAG] = true;
        fprintf(stderr, "AMONET_MICROLOADER\n");

        // The real header is shifted, copy to temporary buffer
        h = reinterpret_cast<const boot_img_hdr_v0*>(addr + AMONET_MICROLOADER_SZ);
        auto real_hdr_sz = h->page_size - AMONET_MICROLOADER_SZ;
        auto buf = make_unique<uint8_t[]>(h->page_size);
        memcpy(buf.get(), h, real_hdr_sz);

        hdr_addr = addr;
        return make_hdr(buf.get());
    }

    if (CMD_MATCH(NOOKHD_RL_MAGIC) ||
        CMD_MATCH(NOOKHD_GL_MAGIC) ||
        CMD_MATCH(NOOKHD_GR_MAGIC) ||
        CMD_MATCH(NOOKHD_EB_MAGIC) ||
        CMD_MATCH(NOOKHD_ER_MAGIC)) {
        flags[NOOKHD_FLAG] = true;
        fprintf(stderr, "NOOKHD_LOADER\n");
        addr += NOOKHD_PRE_HEADER_SZ;
    } else if (BUFFER_MATCH(h->name, ACCLAIM_MAGIC)) {
        flags[ACCLAIM_FLAG] = true;
        fprintf(stderr, "ACCLAIM_LOADER\n");
        addr += ACCLAIM_PRE_HEADER_SZ;
    }

    // addr could be adjusted
    hdr_addr = addr;
    return make_hdr(addr);
}

#define get_block(name)                 \
name = hdr_addr + off;                  \
off += hdr->name##_size();              \
off = align_to(off, hdr->page_size());

#define get_ignore(name)                                            \
if (hdr->name##_size()) {                                           \
    auto blk_sz = align_to(hdr->name##_size(), hdr->page_size());   \
    ignore_size += blk_sz;                                          \
    off += blk_sz;                                                  \
}

void boot_img::parse_image(const uint8_t *addr, format_t type) {
    hdr = create_hdr(addr, type);

    if (char *id = hdr->id()) {
        for (int i = SHA_DIGEST_SIZE + 4; i < SHA256_DIGEST_SIZE; ++i) {
            if (id[i]) {
                flags[SHA256_FLAG] = true;
                break;
            }
        }
    }

    hdr->print();

    size_t off = hdr->hdr_space();
    get_block(kernel);
    get_block(ramdisk);
    get_block(second);
    get_block(extra);
    get_block(recovery_dtbo);
    get_block(dtb);

    ignore = hdr_addr + off;
    get_ignore(signature)
    get_ignore(vendor_ramdisk_table)
    get_ignore(bootconfig)

    if (auto size = hdr->kernel_size()) {
        if (int dtb_off = find_dtb_offset(kernel, size); dtb_off > 0) {
            kernel_dtb = kernel + dtb_off;
            hdr->kernel_dt_size = size - dtb_off;
            hdr->kernel_size() = dtb_off;
            fprintf(stderr, "%-*s [%u]\n", PADDING, "KERNEL_DTB_SZ", hdr->kernel_dt_size);
        }

        k_fmt = check_fmt_lg(kernel, hdr->kernel_size());
        if (k_fmt == MTK) {
            fprintf(stderr, "MTK_KERNEL_HDR\n");
            flags[MTK_KERNEL] = true;
            k_hdr = reinterpret_cast<const mtk_hdr *>(kernel);
            fprintf(stderr, "%-*s [%u]\n", PADDING, "SIZE", k_hdr->size);
            fprintf(stderr, "%-*s [%s]\n", PADDING, "NAME", k_hdr->name);
            kernel += sizeof(mtk_hdr);
            hdr->kernel_size() -= sizeof(mtk_hdr);
            k_fmt = check_fmt_lg(kernel, hdr->kernel_size());
        }
        if (k_fmt == ZIMAGE) {
            z_hdr = reinterpret_cast<const zimage_hdr *>(kernel);
            if (void *gzip_offset = memmem(kernel, hdr->kernel_size(), GZIP1_MAGIC "\x08\x00", 4)) {
                fprintf(stderr, "ZIMAGE_KERNEL\n");
                z_info.hdr_sz = (uint8_t *) gzip_offset - kernel;

                // Find end of piggy
                uint32_t zImage_size = z_hdr->end - z_hdr->start;
                uint32_t piggy_end = zImage_size;
                uint32_t offsets[16];
                memcpy(offsets, kernel + zImage_size - sizeof(offsets), sizeof(offsets));
                for (int i = 15; i >= 0; --i) {
                    if (offsets[i] > (zImage_size - 0xFF) && offsets[i] < zImage_size) {
                        piggy_end = offsets[i];
                        break;
                    }
                }

                if (piggy_end == zImage_size) {
                    fprintf(stderr, "! Could not find end of zImage piggy, keeping raw kernel\n");
                } else {
                    flags[ZIMAGE_KERNEL] = true;
                    z_info.tail = kernel + piggy_end;
                    z_info.tail_sz = hdr->kernel_size() - piggy_end;
                    kernel += z_info.hdr_sz;
                    hdr->kernel_size() = piggy_end - z_info.hdr_sz;
                    k_fmt = check_fmt_lg(kernel, hdr->kernel_size());
                }
            } else {
                fprintf(stderr, "! Could not find zImage gzip piggy, keeping raw kernel\n");
            }
        }
        fprintf(stderr, "%-*s [%s]\n", PADDING, "KERNEL_FMT", fmt2name[k_fmt]);
    }
    if (auto size = hdr->ramdisk_size()) {
        if (hdr->is_vendor && hdr->header_version() >= 4) {
            // v4 vendor boot contains multiple ramdisks
            // Do not try to mess with it for now
            r_fmt = UNKNOWN;
        } else {
            r_fmt = check_fmt_lg(ramdisk, size);
        }
        if (r_fmt == MTK) {
            fprintf(stderr, "MTK_RAMDISK_HDR\n");
            flags[MTK_RAMDISK] = true;
            r_hdr = reinterpret_cast<const mtk_hdr *>(ramdisk);
            fprintf(stderr, "%-*s [%u]\n", PADDING, "SIZE", r_hdr->size);
            fprintf(stderr, "%-*s [%s]\n", PADDING, "NAME", r_hdr->name);
            ramdisk += sizeof(mtk_hdr);
            hdr->ramdisk_size() -= sizeof(mtk_hdr);
            r_fmt = check_fmt_lg(ramdisk, hdr->ramdisk_size());
        }
        fprintf(stderr, "%-*s [%s]\n", PADDING, "RAMDISK_FMT", fmt2name[r_fmt]);
    }
    if (auto size = hdr->extra_size()) {
        e_fmt = check_fmt_lg(extra, size);
        fprintf(stderr, "%-*s [%s]\n", PADDING, "EXTRA_FMT", fmt2name[e_fmt]);
    }

    if (addr + off < map.buf + map.sz) {
        tail = addr + off;
        tail_size = map.buf + map.sz - tail;

        // Check special flags
        if (tail_size >= 16 && BUFFER_MATCH(tail, SEANDROID_MAGIC)) {
            fprintf(stderr, "SAMSUNG_SEANDROID\n");
            flags[SEANDROID_FLAG] = true;
        } else if (tail_size >= 16 && BUFFER_MATCH(tail, LG_BUMP_MAGIC)) {
            fprintf(stderr, "LG_BUMP_IMAGE\n");
            flags[LG_BUMP_FLAG] = true;
        }

        // Find AVB footer
        const void *footer = tail + tail_size - sizeof(AvbFooter);
        if (BUFFER_MATCH(footer, AVB_FOOTER_MAGIC)) {
            avb_footer = reinterpret_cast<const AvbFooter*>(footer);
            // Double check if meta header exists
            const void *meta = hdr_addr + __builtin_bswap64(avb_footer->vbmeta_offset);
            if (BUFFER_MATCH(meta, AVB_MAGIC)) {
                fprintf(stderr, "VBMETA\n");
                flags[AVB_FLAG] = true;
                vbmeta = reinterpret_cast<const AvbVBMetaImageHeader*>(meta);
            }
        }
    }
}

int split_image_dtb(const char *filename) {
    auto img = mmap_data(filename);

    if (int off = find_dtb_offset(img.buf, img.sz); off > 0) {
        format_t fmt = check_fmt_lg(img.buf, img.sz);
        if (COMPRESSED(fmt)) {
            int fd = creat(KERNEL_FILE, 0644);
            decompress(fmt, fd, img.buf, off);
            close(fd);
        } else {
            dump(img.buf, off, KERNEL_FILE);
        }
        dump(img.buf + off, img.sz - off, KER_DTB_FILE);
        return 0;
    } else {
        fprintf(stderr, "Cannot find DTB in %s\n", filename);
        return 1;
    }
}

int unpack(const char *image, bool skip_decomp, bool hdr) {
    boot_img boot(image);

    if (hdr)
        boot.hdr->dump_hdr_file();

    // Dump kernel
    if (!skip_decomp && COMPRESSED(boot.k_fmt)) {
        if (boot.hdr->kernel_size() != 0) {
            int fd = creat(KERNEL_FILE, 0644);
            decompress(boot.k_fmt, fd, boot.kernel, boot.hdr->kernel_size());
            close(fd);
        }
    } else {
        dump(boot.kernel, boot.hdr->kernel_size(), KERNEL_FILE);
    }

    // Dump kernel_dtb
    dump(boot.kernel_dtb, boot.hdr->kernel_dt_size, KER_DTB_FILE);

    // Dump ramdisk
    if (!skip_decomp && COMPRESSED(boot.r_fmt)) {
        if (boot.hdr->ramdisk_size() != 0) {
            int fd = creat(RAMDISK_FILE, 0644);
            decompress(boot.r_fmt, fd, boot.ramdisk, boot.hdr->ramdisk_size());
            close(fd);
        }
    } else {
        dump(boot.ramdisk, boot.hdr->ramdisk_size(), RAMDISK_FILE);
    }

    // Dump second
    dump(boot.second, boot.hdr->second_size(), SECOND_FILE);

    // Dump extra
    if (!skip_decomp && COMPRESSED(boot.e_fmt)) {
        if (boot.hdr->extra_size() != 0) {
            int fd = creat(EXTRA_FILE, 0644);
            decompress(boot.e_fmt, fd, boot.extra, boot.hdr->extra_size());
            close(fd);
        }
    } else {
        dump(boot.extra, boot.hdr->extra_size(), EXTRA_FILE);
    }

    // Dump recovery_dtbo
    dump(boot.recovery_dtbo, boot.hdr->recovery_dtbo_size(), RECV_DTBO_FILE);

    // Dump dtb
    dump(boot.dtb, boot.hdr->dtb_size(), DTB_FILE);

    return boot.flags[CHROMEOS_FLAG] ? 2 : 0;
}

#define file_align_with(page_size) \
write_zero(fd, align_padding(lseek(fd, 0, SEEK_CUR) - off.header, page_size))

#define file_align() file_align_with(boot.hdr->page_size())

void repack(const char *src_img, const char *out_img, bool skip_comp) {
    const boot_img boot(src_img);
    fprintf(stderr, "Repack to image: [%s]\n", out_img);

    struct {
        uint32_t header;
        uint32_t kernel;
        uint32_t ramdisk;
        uint32_t second;
        uint32_t extra;
        uint32_t dtb;
        uint32_t total;
        uint32_t vbmeta;
    } off{};

    // Create a new boot header and reset sizes
    auto hdr = boot.hdr->clone();
    hdr->kernel_size() = 0;
    hdr->ramdisk_size() = 0;
    hdr->second_size() = 0;
    hdr->dtb_size() = 0;
    hdr->kernel_dt_size = 0;

    if (access(HEADER_FILE, R_OK) == 0)
        hdr->load_hdr_file();

    /***************
     * Write blocks
     ***************/

    // Create new image
    int fd = creat(out_img, 0644);

    if (boot.flags[DHTB_FLAG]) {
        // Skip DHTB header
        write_zero(fd, sizeof(dhtb_hdr));
    } else if (boot.flags[BLOB_FLAG]) {
        xwrite(fd, boot.map.buf, sizeof(blob_hdr));
    } else if (boot.flags[NOOKHD_FLAG]) {
        xwrite(fd, boot.map.buf, NOOKHD_PRE_HEADER_SZ);
    } else if (boot.flags[ACCLAIM_FLAG]) {
        xwrite(fd, boot.map.buf, ACCLAIM_PRE_HEADER_SZ);
    }

    // Copy raw header
    off.header = lseek(fd, 0, SEEK_CUR);
    xwrite(fd, boot.hdr_addr, hdr->hdr_space());

    // kernel
    off.kernel = lseek(fd, 0, SEEK_CUR);
    if (boot.flags[MTK_KERNEL]) {
        // Copy MTK headers
        xwrite(fd, boot.k_hdr, sizeof(mtk_hdr));
    }
    if (boot.flags[ZIMAGE_KERNEL]) {
        // Copy zImage headers
        xwrite(fd, boot.z_hdr, boot.z_info.hdr_sz);
    }
    if (access(KERNEL_FILE, R_OK) == 0) {
        auto m = mmap_data(KERNEL_FILE);
        if (!skip_comp && !COMPRESSED_ANY(check_fmt(m.buf, m.sz)) && COMPRESSED(boot.k_fmt)) {
            // Always use zopfli for zImage compression
            auto fmt = (boot.flags[ZIMAGE_KERNEL] && boot.k_fmt == GZIP) ? ZOPFLI : boot.k_fmt;
            hdr->kernel_size() = compress(fmt, fd, m.buf, m.sz);
        } else {
            hdr->kernel_size() = xwrite(fd, m.buf, m.sz);
        }

        if (boot.flags[ZIMAGE_KERNEL]) {
            if (hdr->kernel_size() > boot.hdr->kernel_size()) {
                fprintf(stderr, "! Recompressed kernel is too large, using original kernel\n");
                ftruncate64(fd, lseek64(fd, - (off64_t) hdr->kernel_size(), SEEK_CUR));
                xwrite(fd, boot.kernel, boot.hdr->kernel_size());
            } else if (!skip_comp) {
                // Pad zeros to make sure the zImage file size does not change
                // Also ensure the last 4 bytes are the uncompressed vmlinux size
                uint32_t sz = m.sz;
                write_zero(fd, boot.hdr->kernel_size() - hdr->kernel_size() - sizeof(sz));
                xwrite(fd, &sz, sizeof(sz));
            }

            // zImage size shall remain the same
            hdr->kernel_size() = boot.hdr->kernel_size();
        }
    } else if (boot.hdr->kernel_size() != 0) {
        xwrite(fd, boot.kernel, boot.hdr->kernel_size());
        hdr->kernel_size() = boot.hdr->kernel_size();
    }
    if (boot.flags[ZIMAGE_KERNEL]) {
        // Copy zImage tail and adjust size accordingly
        hdr->kernel_size() += boot.z_info.hdr_sz;
        hdr->kernel_size() += xwrite(fd, boot.z_info.tail, boot.z_info.tail_sz);
    }

    // kernel dtb
    if (access(KER_DTB_FILE, R_OK) == 0)
        hdr->kernel_size() += restore(fd, KER_DTB_FILE);
    file_align();

    // ramdisk
    off.ramdisk = lseek(fd, 0, SEEK_CUR);
    if (boot.flags[MTK_RAMDISK]) {
        // Copy MTK headers
        xwrite(fd, boot.r_hdr, sizeof(mtk_hdr));
    }
    if (access(RAMDISK_FILE, R_OK) == 0) {
        auto m = mmap_data(RAMDISK_FILE);
        auto r_fmt = boot.r_fmt;
        if (!skip_comp && !hdr->is_vendor && hdr->header_version() == 4 && r_fmt != LZ4_LEGACY) {
            // A v4 boot image ramdisk will have to be merged with other vendor ramdisks,
            // and they have to use the exact same compression method. v4 GKIs are required to
            // use lz4 (legacy), so hardcode the format here.
            fprintf(stderr, "RAMDISK_FMT: [%s] -> [%s]\n", fmt2name[r_fmt], fmt2name[LZ4_LEGACY]);
            r_fmt = LZ4_LEGACY;
        }
        if (!skip_comp && !COMPRESSED_ANY(check_fmt(m.buf, m.sz)) && COMPRESSED(r_fmt)) {
            hdr->ramdisk_size() = compress(r_fmt, fd, m.buf, m.sz);
        } else {
            hdr->ramdisk_size() = xwrite(fd, m.buf, m.sz);
        }
        file_align();
    }

    // second
    off.second = lseek(fd, 0, SEEK_CUR);
    if (access(SECOND_FILE, R_OK) == 0) {
        hdr->second_size() = restore(fd, SECOND_FILE);
        file_align();
    }

    // extra
    off.extra = lseek(fd, 0, SEEK_CUR);
    if (access(EXTRA_FILE, R_OK) == 0) {
        auto m = mmap_data(EXTRA_FILE);
        if (!skip_comp && !COMPRESSED_ANY(check_fmt(m.buf, m.sz)) && COMPRESSED(boot.e_fmt)) {
            hdr->extra_size() = compress(boot.e_fmt, fd, m.buf, m.sz);
        } else {
            hdr->extra_size() = xwrite(fd, m.buf, m.sz);
        }
        file_align();
    }

    // recovery_dtbo
    if (access(RECV_DTBO_FILE, R_OK) == 0) {
        hdr->recovery_dtbo_offset() = lseek(fd, 0, SEEK_CUR);
        hdr->recovery_dtbo_size() = restore(fd, RECV_DTBO_FILE);
        file_align();
    }

    // dtb
    off.dtb = lseek(fd, 0, SEEK_CUR);
    if (access(DTB_FILE, R_OK) == 0) {
        hdr->dtb_size() = restore(fd, DTB_FILE);
        file_align();
    }

    // Directly copy ignored blobs
    if (boot.ignore_size) {
        // ignore_size should already be aligned
        xwrite(fd, boot.ignore, boot.ignore_size);
    }

    // Proprietary stuffs
    if (boot.flags[SEANDROID_FLAG]) {
        xwrite(fd, SEANDROID_MAGIC, 16);
        if (boot.flags[DHTB_FLAG]) {
            xwrite(fd, "\xFF\xFF\xFF\xFF", 4);
        }
    } else if (boot.flags[LG_BUMP_FLAG]) {
        xwrite(fd, LG_BUMP_MAGIC, 16);
    }

    off.total = lseek(fd, 0, SEEK_CUR);
    file_align();

    // vbmeta
    if (boot.flags[AVB_FLAG]) {
        // According to avbtool.py, if the input is not an Android sparse image
        // (which boot images are not), the default block size is 4096
        file_align_with(4096);
        off.vbmeta = lseek(fd, 0, SEEK_CUR);
        uint64_t vbmeta_size = __builtin_bswap64(boot.avb_footer->vbmeta_size);
        xwrite(fd, boot.vbmeta, vbmeta_size);
    }

    // Pad image to original size if not chromeos (as it requires post processing)
    if (!boot.flags[CHROMEOS_FLAG]) {
        off_t current = lseek(fd, 0, SEEK_CUR);
        if (current < boot.map.sz) {
            write_zero(fd, boot.map.sz - current);
        }
    }

    close(fd);

    /******************
     * Patch the image
     ******************/

    // Map output image as rw
    auto out = mmap_data(out_img, true);

    // MTK headers
    if (boot.flags[MTK_KERNEL]) {
        auto m_hdr = reinterpret_cast<mtk_hdr *>(out.buf + off.kernel);
        m_hdr->size = hdr->kernel_size();
        hdr->kernel_size() += sizeof(mtk_hdr);
    }
    if (boot.flags[MTK_RAMDISK]) {
        auto m_hdr = reinterpret_cast<mtk_hdr *>(out.buf + off.ramdisk);
        m_hdr->size = hdr->ramdisk_size();
        hdr->ramdisk_size() += sizeof(mtk_hdr);
    }

    // Make sure header size matches
    hdr->header_size() = hdr->hdr_size();

    // Update checksum
    if (char *id = hdr->id()) {
        HASH_CTX ctx;
        boot.flags[SHA256_FLAG] ? SHA256_init(&ctx) : SHA_init(&ctx);
        uint32_t size = hdr->kernel_size();
        HASH_update(&ctx, out.buf + off.kernel, size);
        HASH_update(&ctx, &size, sizeof(size));
        size = hdr->ramdisk_size();
        HASH_update(&ctx, out.buf + off.ramdisk, size);
        HASH_update(&ctx, &size, sizeof(size));
        size = hdr->second_size();
        HASH_update(&ctx, out.buf + off.second, size);
        HASH_update(&ctx, &size, sizeof(size));
        size = hdr->extra_size();
        if (size) {
            HASH_update(&ctx, out.buf + off.extra, size);
            HASH_update(&ctx, &size, sizeof(size));
        }
        uint32_t ver = hdr->header_version();
        if (ver == 1 || ver == 2) {
            size = hdr->recovery_dtbo_size();
            HASH_update(&ctx, out.buf + hdr->recovery_dtbo_offset(), size);
            HASH_update(&ctx, &size, sizeof(size));
        }
        if (ver == 2) {
            size = hdr->dtb_size();
            HASH_update(&ctx, out.buf + off.dtb, size);
            HASH_update(&ctx, &size, sizeof(size));
        }
        memset(id, 0, BOOT_ID_SIZE);
        memcpy(id, HASH_final(&ctx), boot.flags[SHA256_FLAG] ? SHA256_DIGEST_SIZE : SHA_DIGEST_SIZE);
    }

    // Print new header info
    hdr->print();

    // Copy main header
    if (boot.flags[AMONET_FLAG]) {
        auto real_hdr_sz = std::min(hdr->hdr_space() - AMONET_MICROLOADER_SZ, hdr->hdr_size());
        memcpy(out.buf + off.header + AMONET_MICROLOADER_SZ, hdr->raw_hdr(), real_hdr_sz);
    } else {
        memcpy(out.buf + off.header, hdr->raw_hdr(), hdr->hdr_size());
    }

    if (boot.flags[AVB_FLAG]) {
        // Copy and patch AVB structures
        auto footer = reinterpret_cast<AvbFooter*>(out.buf + out.sz - sizeof(AvbFooter));
        auto vbmeta = reinterpret_cast<AvbVBMetaImageHeader*>(out.buf + off.vbmeta);
        memcpy(footer, boot.avb_footer, sizeof(AvbFooter));
        footer->original_image_size = __builtin_bswap64(off.total);
        footer->vbmeta_offset = __builtin_bswap64(off.vbmeta);
        if (check_env("PATCHVBMETAFLAG")) {
            vbmeta->flags = __builtin_bswap32(3);
        }
    }

    if (boot.flags[DHTB_FLAG]) {
        // DHTB header
        auto d_hdr = reinterpret_cast<dhtb_hdr *>(out.buf);
        memcpy(d_hdr, DHTB_MAGIC, 8);
        d_hdr->size = off.total - sizeof(dhtb_hdr);
        SHA256_hash(out.buf + sizeof(dhtb_hdr), d_hdr->size, d_hdr->checksum);
    } else if (boot.flags[BLOB_FLAG]) {
        // Blob header
        auto b_hdr = reinterpret_cast<blob_hdr *>(out.buf);
        b_hdr->size = off.total - sizeof(blob_hdr);
    }
}