OF: Add a separate direct kernel loading word

Currently, go-64 is used for booting a kernel from qemu (i.e. -kernel).
However, there is an expectation from users that this should be able to
boot not just vmlinux kernels but things like Zimages too.

The bootwrapper of a BE zImage is a 32-bit ELF. Attempting to load that
with go-64 means that it will be ran with MSR_SF set (64-bit mode). This
crashes early in boot (usually due to what should be 32-bit operations
being done with 64-bit registers eventually leading to an incorrect
address being generated and branched to).

Note that our 64-bit payloads are prepared to enter with MSR_SF cleared
and set it themselves very early.

Add a new word named go-direct that will execute any simple payload
in-place and will enter with MSR_SF cleared. This allows booting a BE
zImage from qemu with -machine kernel-addr=0.

Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>

1 files changed, 6 insertions, 0 deletions

diff --git a/slof/fs/boot.fs b/slof/fs/boot.fs
index 6d16c54..a6dfdf3 100644
--- a/slof/fs/boot.fs
+++ b/slof/fs/boot.fs
@@ -112,6 +112,12 @@ defer go ( -- )
     claim-list elf-release 0 to claim-list
 ;
 
+: go-direct ( -- )
+    0 ciregs >r3 ! 0 ciregs >r4 ! 0 ciregs >r2 !
+    msr@ 7fffffffffffffff and 2000 or ciregs >srr1 !
+    go-args 2@ go-entry call-client
+;
+
 : set-le ( -- )
     1 ciregs >r13 !
 ;