Re: [PATCH 2/2] selftests: KVM: Fix 'asm-operand-width' warnings in steal_time.c

Andrew Jones
2021-09-21T07:19:20Z

On Tue, Sep 21, 2021 at 01:01:20AM +0000, Oliver Upton wrote:
> Building steal_time.c for arm64 with clang throws the following:
>
> >> steal_time.c:130:22: error: value size does not match register size specified by the constraint and modifier [-Werror,-Wasm-operand-widths]
> : "=r" (ret) : "r" (func), "r" (arg) :
> ^
> >> steal_time.c:130:34: error: value size does not match register size specified by the constraint and modifier [-Werror,-Wasm-operand-widths]
> : "=r" (ret) : "r" (func), "r" (arg) :
> ^
>
> Silence by casting operands to 64 bits.
>
> Signed-off-by: Oliver Upton <oupton@google.com>
> ---
> tools/testing/selftests/kvm/steal_time.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/kvm/steal_time.c b/tools/testing/selftests/kvm/steal_time.c
> index ecec30865a74..eb75b31122c5 100644
> --- a/tools/testing/selftests/kvm/steal_time.c
> +++ b/tools/testing/selftests/kvm/steal_time.c
> @@ -127,7 +127,7 @@ static int64_t smccc(uint32_t func, uint32_t arg)
> "mov x1, %2\n"
> "hvc #0\n"
> "mov %0, x0\n"
> - : "=r" (ret) : "r" (func), "r" (arg) :
> + : "=r" (ret) : "r" ((uint64_t)func), "r" ((uint64_t)arg) :

Actually, I think I'd rather fix this smccc implementation to match the
spec, which I think should be done like this

diff --git a/tools/testing/selftests/kvm/steal_time.c b/tools/testing/selftests/kvm/steal_time.c
index ecec30865a74..7da957259ce4 100644
--- a/tools/testing/selftests/kvm/steal_time.c
+++ b/tools/testing/selftests/kvm/steal_time.c
@@ -118,12 +118,12 @@ struct st_time {
uint64_t st_time;
};

-static int64_t smccc(uint32_t func, uint32_t arg)
+static int64_t smccc(uint32_t func, uint64_t arg)
{
unsigned long ret;

asm volatile(
- "mov x0, %1\n"
+ "mov w0, %w1\n"
"mov x1, %2\n"
"hvc #0\n"
"mov %0, x0\n"

Thanks,
drew

> "x0", "x1", "x2", "x3");
>
> return ret;
> --
> 2.33.0.464.g1972c5931b-goog
>