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

Janosch Frank
2023-04-04T11:21:34Z

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@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

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

Reviewed-by: Janosch Frank <frankja@linux.ibm.com>

> 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