Re: [Qemu-devel] [PATCH] multiboot: mh_load_end_addr and mh_bss_end_addr may be zero

[Kevin Wolf]

Am 23.01.2012 13:49, schrieb Göran Weinholt:
> There are two special cases in the address fields of the multiboot
> format. If mh_load_end_addr is zero then the whole image file should
> be loaded and if mh_bss_end_addr is zero then there is no bss segment.
> With this change it is again possible to boot kernels where these
> fields are zero.
> 
> Signed-off-by: Göran Weinholt <address@hidden>
> Tested-by: Alexander Graf <address@hidden>
> ---
>  hw/multiboot.c |   15 ++++++++++++++-
>  1 files changed, 14 insertions(+), 1 deletions(-)
> 
> diff --git a/hw/multiboot.c b/hw/multiboot.c
> index b4484a3..db28328 100644
> --- a/hw/multiboot.c
> +++ b/hw/multiboot.c
> @@ -202,10 +202,23 @@ int load_multiboot(void *fw_cfg,
>          uint32_t mh_bss_end_addr = ldl_p(header+i+24);
>          mh_load_addr = ldl_p(header+i+16);
>          uint32_t mb_kernel_text_offset = i - (mh_header_addr - mh_load_addr);
> -        uint32_t mb_load_size = mh_load_end_addr - mh_load_addr;
> +        uint32_t mb_load_size;
> +
> +        /* A load end address of zero indicates that the whole file
> +         * should be loaded. */
> +        if (!mh_load_end_addr) {
> +            mh_load_end_addr = kernel_file_size + mh_load_addr;

This is only right if the OS image starts at offset 0 in the image file.
IIUC, in the general case it starts at byte i - (mh_header_addr -
mh_load_addr), so you need to subtract this from kernel_file_size.

Kevin