Re: [PATCH] KVM: s390: get rid of register asm usage

Christian Borntraeger
2021-06-22T14:58:05Z

On 21.06.21 16:03, Heiko Carstens wrote:
> Using register asm statements has been proven to be very error prone,
> especially when using code instrumentation where gcc may add function
> calls, which clobbers register contents in an unexpected way.
>
> Therefore get rid of register asm statements in kvm code, even though
> there is currently nothing wrong with them. This way we know for sure
> that this bug class won't be introduced here.
>
> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
> Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

thanks applied.

> ---
> arch/s390/kvm/kvm-s390.c | 18 +++++++++---------
> 1 file changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 1296fc10f80c..4b7b24f07790 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -329,31 +329,31 @@ static void allow_cpu_feat(unsigned long nr)
>
> static inline int plo_test_bit(unsigned char nr)
> {
> - register unsigned long r0 asm("0") = (unsigned long) nr | 0x100;
> + unsigned long function = (unsigned long) nr | 0x100;
> int cc;
>
> asm volatile(
> + " lgr 0,%[function]\n"
> /* Parameter registers are ignored for "test bit" */
> " plo 0,0,0,0(0)\n"
> " ipm %0\n"
> " srl %0,28\n"
> : "=d" (cc)
> - : "d" (r0)
> - : "cc");
> + : [function] "d" (function)
> + : "cc", "0");
> return cc == 0;
> }
>
> static __always_inline void __insn32_query(unsigned int opcode, u8 *query)
> {
> - register unsigned long r0 asm("0") = 0; /* query function */
> - register unsigned long r1 asm("1") = (unsigned long) query;
> -
> asm volatile(
> - /* Parameter regs are ignored */
> + " lghi 0,0\n"
> + " lgr 1,%[query]\n"
> + /* Parameter registers are ignored */
> " .insn rrf,%[opc] << 16,2,4,6,0\n"
> :
> - : "d" (r0), "a" (r1), [opc] "i" (opcode)
> - : "cc", "memory");
> + : [query] "d" ((unsigned long)query), [opc] "i" (opcode)
> + : "cc", "memory", "0", "1");
> }
>
> #define INSN_SORTL 0xb938
>