Re: [PATCH v6 7/7] kselftest/arm64: Add HWCAP test for FEAT_{LS64, LS64_V}

["Arnd Bergmann" <arnd@arndb.de>]

On Fri, Oct 24, 2025, at 11:08, Zhou Wang wrote:

> +static void ls64_sigill(void)
> +{
> +	struct sigaction ign, old;
> +	char src[64] __aligned(64) = { 1 };
> +
> +	/*
> +	 * LS64, LS64_V require target memory to be Device/Non-cacheable (if
> +	 * FEAT_LS64WB not supported) and the completer supports these
> +	 * instructions, otherwise we'll receive a SIGBUS. Since we are only
> +	 * testing the ABI here, so just ignore the SIGBUS and see if we can
> +	 * execute the instructions without receiving a SIGILL. Restore the
> +	 * handler of SIGBUS after this test.
> +	 */
> +	ign.sa_sigaction = ignore_signal;
> +	ign.sa_flags = SA_SIGINFO | SA_RESTART;
> +	sigemptyset(&ign.sa_mask);
> +	sigaction(SIGBUS, &ign, &old);
> +
> +	register void *xn asm ("x8") = src;
> +	register u64 xt_1 asm ("x0");
> +	register u64 __maybe_unused xt_2 asm ("x1");
> +	register u64 __maybe_unused xt_3 asm ("x2");
> +	register u64 __maybe_unused xt_4 asm ("x3");
> +	register u64 __maybe_unused xt_5 asm ("x4");
> +	register u64 __maybe_unused xt_6 asm ("x5");
> +	register u64 __maybe_unused xt_7 asm ("x6");
> +	register u64 __maybe_unused xt_8 asm ("x7");
> +
> +	/* LD64B x0, [x8] */
> +	asm volatile(".inst 0xf83fd100" : "=r" (xt_1) : "r" (xn));

Relying on the __maybe_unused register declaration seems a little
fragile, can you change this so that the inline asm specifies
all of the registers correctly as input/output arguments?

> +static void ls64_v_sigill(void)
> +{
> +	struct sigaction ign, old;
> +	char dst[64] __aligned(64);
> +
> +	/* See comment in ls64_sigill() */
> +	ign.sa_sigaction = ignore_signal;
> +	ign.sa_flags = SA_SIGINFO | SA_RESTART;
> +	sigemptyset(&ign.sa_mask);
> +	sigaction(SIGBUS, &ign, &old);
> +
> +	register void *xn asm ("x8") = dst;
> +	register u64 xt_1 asm ("x0") = 1;
> +	register u64 __maybe_unused xt_2 asm ("x1") = 2;
> +	register u64 __maybe_unused xt_3 asm ("x2") = 3;
> +	register u64 __maybe_unused xt_4 asm ("x3") = 4;
> +	register u64 __maybe_unused xt_5 asm ("x4") = 5;
> +	register u64 __maybe_unused xt_6 asm ("x5") = 6;
> +	register u64 __maybe_unused xt_7 asm ("x6") = 7;
> +	register u64 __maybe_unused xt_8 asm ("x7") = 8;
> +	register u64 st   asm ("x9");
> +
> +	/* ST64BV x9, x0, [x8] */
> +	asm volatile(".inst 0xf829b100" : "=r" (st) : "r" (xt_1), "r" (xn));
> +
> +	sigaction(SIGBUS, &old, NULL);

Is ST64BV expected to cause SIGBUS here, or should it return the
0xffffffffffffffff output to indicate an unsupported memory area?

     Arnd