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

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On 4/4/23 12:14, Thomas Huth wrote:
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@xxxxxxxxxx>
---
  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

Eh, I would have left that in, it doesn't hurt us after all.

Reviewed-by: Janosch Frank <frankja@xxxxxxxxxxxxx>

  	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




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