Re: [Qemu-devel] [PATCH 6/6] hw/arm/boot: enable DTB support when booting ELF images

[Peter Maydell]

On 5 September 2014 16:15, Ard Biesheuvel <address@hidden> wrote:
> Add support for loading DTB images when booting ELF images via -kernel.
> The DTB image is located at the next 4 KB boundary above the highest address
> covered by the loaded ELF image.
>
> Signed-off-by: Ard Biesheuvel <address@hidden>
> ---
>  hw/arm/boot.c | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/hw/arm/boot.c b/hw/arm/boot.c
> index 8d8653978dfe..60c4f6af7884 100644
> --- a/hw/arm/boot.c
> +++ b/hw/arm/boot.c
> @@ -458,7 +458,7 @@ void arm_load_kernel(ARMCPU *cpu, struct arm_boot_info 
> *info)
>      int kernel_size;
>      int initrd_size;
>      int is_linux = 0;
> -    uint64_t elf_entry;
> +    uint64_t elf_entry, elf_low_addr;
>      int elf_machine;
>      hwaddr entry, kernel_load_offset;
>      int big_endian;
> @@ -529,7 +529,21 @@ void arm_load_kernel(ARMCPU *cpu, struct arm_boot_info 
> *info)
>
>      /* Assume that raw images are linux kernels, and ELF images are not.  */
>      kernel_size = load_elf(info->kernel_filename, NULL, NULL, &elf_entry,
> -                           NULL, NULL, big_endian, elf_machine, 1);
> +                           &elf_low_addr, NULL, big_endian, elf_machine, 1);
> +    if (kernel_size > 0 && have_dtb(info)) {
> +        /* If we have a DTB in combination with an ELF executable image,
> +         * put the DTB at the base of RAM like we do for bootloaders.
> +         */
> +        uint32_t dtb_size;
> +
> +        if (load_dtb(info->loader_start, info, &dtb_size)) {
> +            exit(1);
> +        }
> +        if (info->loader_start + dtb_size > elf_low_addr) {
> +            fprintf(stderr, "Image %s overlaps DTB\n", 
> info->kernel_filename);
> +            exit(1);
> +        }
> +    }

This shouldn't abort. The reason we need to manually check
for overlap is because the default rom-blob behaviour of
"overlap means don't start QEMU" isn't what we want.
In particular, boards like virt which autogenerate DTBs
will always have_dtb(), but we don't want to prevent
non-DTB-aware ELF blobs from loading anywhere they like.
The behaviour we need is "if blobs don't overlap then
load both, otherwise load the ELF file and ignore the
DTB".

(Thinking about it, that implies we either need a
rom_del_blob() or we need to tell load_dtb() about
areas of address space it needs to check for overlap
with before it registers the rom blob for the dtb.)

thanks
-- PMM