Re: [Qemu-devel] [PATCH v4] aarch64: Allow -kernel option to take a gzip-compressed kernel.

[Peter Crosthwaite]

On Sun, Aug 3, 2014 at 1:45 AM, Richard W.M. Jones <address@hidden> wrote:
> On aarch64 it is the bootloader's job to uncompress the kernel.  UEFI
> and u-boot bootloaders do this automatically when the kernel is
> gzip-compressed.
>
> However the qemu -kernel option does not do this.  The following
> command does not work:
>
>   qemu-system-aarch64 [...] -kernel /boot/vmlinuz
>
> because it tries to execute the gzip-compressed data.
>
> This commit lets gzip-compressed kernels be uncompressed
> transparently.
>
> Currently this is only done when emulating aarch64.
>
> Signed-off-by: Richard W.M. Jones <address@hidden>
> ---
>  hw/arm/boot.c       |  9 +++++++++
>  hw/core/loader.c    | 43 +++++++++++++++++++++++++++++++++++++++++++
>  include/hw/loader.h |  1 +

There's two patches here, one adding the generic gzip loader (which
has wider review audience than just ARM people), and a second one
adding the AArch64 usage.

>  3 files changed, 53 insertions(+)
>
> diff --git a/hw/arm/boot.c b/hw/arm/boot.c
> index 3d1f4a2..1d541db 100644
> --- a/hw/arm/boot.c
> +++ b/hw/arm/boot.c
> @@ -444,6 +444,7 @@ static void do_cpu_reset(void *opaque)
>  void arm_load_kernel(ARMCPU *cpu, struct arm_boot_info *info)
>  {
>      CPUState *cs = CPU(cpu);
> +    int allow_compressed_kernels = 0;
>      int kernel_size;
>      int initrd_size;
>      int is_linux = 0;
> @@ -465,6 +466,7 @@ void arm_load_kernel(ARMCPU *cpu, struct arm_boot_info 
> *info)
>          primary_loader = bootloader_aarch64;
>          kernel_load_offset = KERNEL64_LOAD_ADDR;
>          elf_machine = EM_AARCH64;
> +        allow_compressed_kernels = 1;
>      } else {
>          primary_loader = bootloader;
>          kernel_load_offset = KERNEL_LOAD_ADDR;
> @@ -510,6 +512,13 @@ void arm_load_kernel(ARMCPU *cpu, struct arm_boot_info 
> *info)
>          kernel_size = load_uimage(info->kernel_filename, &entry, NULL,
>                                    &is_linux);
>      }
> +    /* On aarch64, it's the bootloader's job to uncompress the kernel. */
> +    if (allow_compressed_kernels && kernel_size < 0) {
> +        entry = info->loader_start + kernel_load_offset;
> +        kernel_size = load_image_gzipped(info->kernel_filename, entry,
> +                                         info->ram_size - 
> kernel_load_offset);
> +        is_linux = 1;
> +    }
>      if (kernel_size < 0) {
>          entry = info->loader_start + kernel_load_offset;
>          kernel_size = load_image_targphys(info->kernel_filename, entry,
> diff --git a/hw/core/loader.c b/hw/core/loader.c
> index 2bf6b8f..1cbe733 100644
> --- a/hw/core/loader.c
> +++ b/hw/core/loader.c
> @@ -577,6 +577,49 @@ int load_ramdisk(const char *filename, hwaddr addr, 
> uint64_t max_sz)
>      return load_uboot_image(filename, NULL, &addr, NULL, IH_TYPE_RAMDISK);
>  }
>
> +/* Load a gzip-compressed kernel (currently used by aarch64). */

No need to refer to "aarch64" in generic code (this comment is likely
to go stale).

> +int load_image_gzipped(const char *filename, hwaddr addr, uint64_t max_sz)
> +{
> +    uint8_t *compressed_data = NULL;
> +    uint8_t *data = NULL;
> +    gsize len;
> +    size_t max_bytes;
> +    ssize_t bytes;
> +    int ret = -1;
> +
> +    if (!g_file_get_contents(filename, (char **) &compressed_data, &len,
> +                             NULL)) {
> +        goto out;
> +    }
> +
> +    /* Is it a gzip-compressed file? */
> +    if (len < 2 ||
> +        compressed_data[0] != '\x1f' ||
> +        compressed_data[1] != '\x8b') {
> +        goto out;
> +    }
> +
> +    max_bytes = UBOOT_MAX_GUNZIP_BYTES;

Why does u-boot's maximum size limit apply here?

Regards,
Peter

> +    if (max_bytes > max_sz) {
> +        max_bytes = max_sz;
> +    }
> +    data = g_malloc(max_bytes);
> +    bytes = gunzip(data, max_bytes, compressed_data, len);
> +    if (bytes < 0) {
> +        fprintf(stderr, "%s: unable to decompress gzipped kernel file\n",
> +                filename);
> +        goto out;
> +    }
> +
> +    rom_add_blob_fixed(filename, data, bytes, addr);
> +    ret = bytes;
> +
> + out:
> +    g_free(compressed_data);
> +    g_free(data);
> +    return ret;
> +}
> +
>  /*
>   * Functions for reboot-persistent memory regions.
>   *  - used for vga bios and option roms.
> diff --git a/include/hw/loader.h b/include/hw/loader.h
> index 796cbf9..00c9117 100644
> --- a/include/hw/loader.h
> +++ b/include/hw/loader.h
> @@ -15,6 +15,7 @@ int get_image_size(const char *filename);
>  int load_image(const char *filename, uint8_t *addr); /* deprecated */
>  int load_image_targphys(const char *filename, hwaddr,
>                          uint64_t max_sz);
> +int load_image_gzipped(const char *filename, hwaddr addr, uint64_t max_sz);
>
>  #define ELF_LOAD_FAILED       -1
>  #define ELF_LOAD_NOT_ELF      -2
> --
> 2.0.1
>
>