Hi Andy,
On 11/25/24 12:31 AM, Andy Shevchenko wrote:
> The init_size description of boot protocol has an example of the runtime
> start address for the compressed bzImage. For non-relocatable kernel
> it relies on the pref_address value (if not 0), but for relocatable case
> only pays respect to the load_addres and kernel_alignment, and it is
> inaccurate for the latter. Boot loader must consider the pref_address
> as the Linux kernel relocates to it before being decompressed as nicely
> described in the commit 43b1d3e68ee7 message.
>
> Due to this inaccuracy some of the bootloaders (*) made a mistake in
> the calculations and if kernel image is big enough, this may lead to
> unbootable configurations.
>
> *)
> In particular, kexec-tools missed that and resently got a couple of
> changes which will be part of v2.0.30 release. For the record,
> the 43b1d3e68ee7 fixed only kernel kexec implementation and also missed
> to update the init_size description.
>
> While at it, make an example C-like looking as it's done elsewhere in
> the document and fix indentation, so the syntax highliting will work
> properly in some editors (vim).
>
> Fixes: 43b1d3e68ee7 ("kexec: Allocate kernel above bzImage's pref_address")
> Fixes: d297366ba692 ("x86: document new bzImage fields")
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> ---
> Documentation/arch/x86/boot.rst | 17 +++++++++++++----
> 1 file changed, 13 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/arch/x86/boot.rst b/Documentation/arch/x86/boot.rst
> index 4fd492cb4970..01f08d94e8df 100644
> --- a/Documentation/arch/x86/boot.rst
> +++ b/Documentation/arch/x86/boot.rst
> @@ -896,10 +896,19 @@ Offset/size: 0x260/4
>
> The kernel runtime start address is determined by the following algorithm::
>
> - if (relocatable_kernel)
> - runtime_start = align_up(load_address, kernel_alignment)
> - else
> - runtime_start = pref_address
> + if ( relocatable_kernel ) {
> + if ( load_address < pref_address )
What's up with the extra spaces around ( and ) ... and inconsistent with
the lines below?
> + load_address = pref_address;
> + runtime_start = align_up(load_address, kernel_alignment);
> + } else {
> + runtime_start = pref_address;
> + }
> +
> +Hence the necessary memory window location and size can be estimated by
> +a boot loader as::
> +
> + memory_window_start = runtime_start;
> + memory_window_size = init_size;
>
> ============ ===============
> Field name: handover_offset
--
~Randy
