[kvm-unit-tests PATCH] s390x/snippets: Fix compilation with Clang 15

[Thomas Huth <thuth@redhat.com>]

Clang complains:

 s390x/snippets/c/cstart.S:22:13: error: invalid operand for instruction
  lghi %r15, stackptr
             ^
Let's load the address with "larl" instead, like we already do
it in s390x/cstart64.S. For this we should also switch to 64-bit
mode first, then we also don't have to clear r15 right in front
of this anymore.

Changing the code here triggered another problem: initial_cr0
must be aligned on a double-word boundary, otherwise the lctlg
instruction will fail with an specification exception. This was
just working by accident so far - add an ".align 8" now to avoid
the problem.

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 s390x/snippets/c/cstart.S | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/s390x/snippets/c/cstart.S b/s390x/snippets/c/cstart.S
index a7d4cd42..c80ccfed 100644
--- a/s390x/snippets/c/cstart.S
+++ b/s390x/snippets/c/cstart.S
@@ -15,12 +15,12 @@ start:
 	larl	%r1, initial_cr0
 	lctlg	%c0, %c0, 0(%r1)
 	/* XOR all registers with themselves to clear them fully. */
-	.irp i, 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
+	.irp i, 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14
 	xgr \i,\i
 	.endr
-	/* 0x3000 is the stack page for now */
-	lghi	%r15, stackptr
 	sam64
+	/* 0x3000 is the stack page for now */
+	larl	%r15, stackptr
 	brasl	%r14, main
 	/*
 	 * If main() returns, we stop the CPU with the code below. We also
@@ -37,6 +37,7 @@ exit:
 	xgr	%r0, %r0
 	sigp    %r2, %r0, SIGP_STOP
 
+	.align 8
 initial_cr0:
 	/* enable AFP-register control, so FP regs (+BFP instr) can be used */
 	.quad	0x0000000000040000
-- 
2.31.1