Re: [PATCH 1/5] watchdog: diag288_wdt: get rid of register asm

Guenter Roeck
2023-02-03T18:17:36Z

On Fri, Feb 03, 2023 at 08:39:54AM +0100, Alexander Egorenkov 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 watchdog code, and make
> sure this bug class cannot happen.
>
> Moreover, remove the register r1 from the clobber list because this
> register is not changed by DIAG 288.
>
> Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
> Signed-off-by: Alexander Egorenkov <egorenar@linux.ibm.com>

Reviewed-by: Guenter Roeck <linux@roeck-us.net>

> ---
> drivers/watchdog/diag288_wdt.c | 15 +++++++--------
> 1 file changed, 7 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/watchdog/diag288_wdt.c b/drivers/watchdog/diag288_wdt.c
> index 6ca5d9515d85..07ebbb709af4 100644
> --- a/drivers/watchdog/diag288_wdt.c
> +++ b/drivers/watchdog/diag288_wdt.c
> @@ -73,20 +73,19 @@ MODULE_ALIAS("vmwatchdog");
> static int __diag288(unsigned int func, unsigned int timeout,
> unsigned long action, unsigned int len)
> {
> - register unsigned long __func asm("2") = func;
> - register unsigned long __timeout asm("3") = timeout;
> - register unsigned long __action asm("4") = action;
> - register unsigned long __len asm("5") = len;
> + union register_pair r1 = { .even = func, .odd = timeout, };
> + union register_pair r3 = { .even = action, .odd = len, };
> int err;
>
> err = -EINVAL;
> asm volatile(
> - " diag %1, %3, 0x288\n"
> - "0: la %0, 0\n"
> + " diag %[r1],%[r3],0x288\n"
> + "0: la %[err],0\n"
> "1:\n"
> EX_TABLE(0b, 1b)
> - : "+d" (err) : "d"(__func), "d"(__timeout),
> - "d"(__action), "d"(__len) : "1", "cc", "memory");
> + : [err] "+d" (err)
> + : [r1] "d" (r1.pair), [r3] "d" (r3.pair)
> + : "cc", "memory");
> return err;
> }
>