Re: [PATCH v4 6/9] target/arm: Factor out code for setting MTE TCF0 field

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

On 24/6/24 07:30, 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/mte_user_helper.h | 38 ++++++++++++++++++++++++++++
>   linux-user/aarch64/target_prctl.h    | 22 ++--------------
>   2 files changed, 40 insertions(+), 20 deletions(-)
>   create mode 100644 linux-user/aarch64/mte_user_helper.h
> 
> diff --git a/linux-user/aarch64/mte_user_helper.h b/linux-user/aarch64/mte_user_helper.h
> new file mode 100644
> index 0000000000..fd92e71c00
> --- /dev/null
> +++ b/linux-user/aarch64/mte_user_helper.h
> @@ -0,0 +1,38 @@
> +/*
> + * ARM MemTag convenience functions.
> + *
> + * This code is licensed under the GNU GPL v2 or later.
> + *
> + * SPDX-License-Identifier: LGPL-2.1-or-later
> + */
> +
> +#ifndef MTE_H
> +#define MTE_H
> +
> +#include "sys/prctl.h"
> +
> +static inline void arm_set_mte_tcf0(CPUArchState *env, abi_long value)
> +{
> +    /*
> +     * 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);

Missing "qemu/bitops.h" header.

> +}
> +
> +#endif /* MTE_H */
> diff --git a/linux-user/aarch64/target_prctl.h b/linux-user/aarch64/target_prctl.h
> index aa8e203c15..ed75b9e4b5 100644
> --- a/linux-user/aarch64/target_prctl.h
> +++ b/linux-user/aarch64/target_prctl.h
> @@ -7,6 +7,7 @@
>   #define AARCH64_TARGET_PRCTL_H
>   
>   #include "target/arm/cpu-features.h"
> +#include "mte_user_helper.h"
>   
>   static abi_long do_prctl_sve_get_vl(CPUArchState *env)
>   {
> @@ -173,26 +174,7 @@ static abi_long do_prctl_set_tagged_addr_ctrl(CPUArchState *env, abi_long arg2)
>       env->tagged_addr_enable = arg2 & PR_TAGGED_ADDR_ENABLE;
>   
>       if (cpu_isar_feature(aa64_mte, cpu)) {
> -        /*
> -         * 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 (arg2 & PR_MTE_TCF_SYNC) {
> -            tcf = 1;
> -        } else if (arg2 & PR_MTE_TCF_ASYNC) {
> -            tcf = 2;
> -        }
> -        env->cp15.sctlr_el[1] = deposit64(env->cp15.sctlr_el[1], 38, 2, tcf);
> +        arm_set_mte_tcf0(env, arg2);
>   
>           /*
>            * Write PR_MTE_TAG to GCR_EL1[Exclude].