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 as presribed by the reStructuredText
specifications, so the syntax highliting will work properly.
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>
---
v2: fixed the style to follow both rST and kernel conventions (Ingo, Randy)
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..ad2d8ddad27f 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)
+ 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
--
2.43.0.rc1.1336.g36b5255a03ac
