Re: [PATCH v2 6/9] target/arm: Factor out code for setting MTE TCF0 field

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 13/6/24 19:21, Gustavo Romero wrote:
> Factor out the code used for setting the MTE TCF0 field from the prctl
> code into a convenient function. Other subsystems, like gdbstub, need to
> set this field as well, so keep it as a separate function to avoid
> duplication and ensure consistency in how this field is set across the
> board.
> 
> Signed-off-by: Gustavo Romero <gustavo.romero@linaro.org>
> ---
>   linux-user/aarch64/target_prctl.h | 22 ++-----------
>   target/arm/mte.h                  | 53 +++++++++++++++++++++++++++++++
>   2 files changed, 55 insertions(+), 20 deletions(-)
>   create mode 100644 target/arm/mte.h


> diff --git a/target/arm/mte.h b/target/arm/mte.h
> new file mode 100644
> index 0000000000..89712aad70
> --- /dev/null
> +++ b/target/arm/mte.h
> @@ -0,0 +1,53 @@
> +/*
> + * ARM MemTag convenience functions.
> + *
> + * Copyright (c) 2024 Linaro, Ltd.
> + *
> + * This library is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU Lesser General Public
> + * License as published by the Free Software Foundation; either
> + * version 2.1 of the License, or (at your option) any later version.
> + *
> + * This library is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public
> + * License along with this library; if not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#ifndef MTE_H
> +#define MTE_H
> +
> +#ifdef CONFIG_TCG
> +#ifdef CONFIG_USER_ONLY
> +#include "sys/prctl.h"
> +
> +static void set_mte_tcf0(CPUArchState *env, abi_long value)

Either declare it inlined (otherwise we'll get multiple symbols
declared if this header is included multiple times), or
preferably only expose the prototype.

Also I'd use the 'arm_' prefix.

> +{
> +    /*
> +     * Write PR_MTE_TCF to SCTLR_EL1[TCF0].
> +     *
> +     * The kernel has a per-cpu configuration for the sysadmin,
> +     * /sys/devices/system/cpu/cpu<N>/mte_tcf_preferred,
> +     * which qemu does not implement.
> +     *
> +     * Because there is no performance difference between the modes, and
> +     * because SYNC is most useful for debugging MTE errors, choose SYNC
> +     * as the preferred mode.  With this preference, and the way the API
> +     * uses only two bits, there is no way for the program to select
> +     * ASYMM mode.
> +     */
> +    unsigned tcf = 0;
> +    if (value & PR_MTE_TCF_SYNC) {
> +        tcf = 1;
> +    } else if (value & PR_MTE_TCF_ASYNC) {
> +        tcf = 2;
> +    }
> +    env->cp15.sctlr_el[1] = deposit64(env->cp15.sctlr_el[1], 38, 2, tcf);
> +}
> +#endif /* CONFIG_USER_ONLY */
> +#endif /* CONFIG_TCG */
> +
> +#endif /* MTE_H */