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

Thomas Huth
2023-04-04T10:15:26Z

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