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 <[email protected]>
Signed-off-by: Alexey Kardashevskiy <[email protected]>

Author: iamjpn

board-qemu/slof/OF.fs

@@ -303,10 +303,9 @@ set-default-console
 : (boot-ram)
     direct-ram-boot-size 0<> IF
         ." Booting from memory..." cr
-        s" go-args 2@ " evaluate
-        direct-ram-boot-base 0
+        s" direct-ram-boot-base to go-entry" evaluate
         s" true state-valid ! " evaluate
-        s" disable-watchdog go-64" evaluate
+        s" disable-watchdog go-direct" evaluate
     THEN
 ;
 

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 !
 ;