Re: [PATCH v6 06/11] target/arm: Factor out code for setting MTE TCF0 field

[Philippe Mathieu-Daudé]

On 28/6/24 07:08, 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/meson.build       |  2 ++
>   linux-user/aarch64/mte_user_helper.c | 34 ++++++++++++++++++++++++++++
>   linux-user/aarch64/mte_user_helper.h | 25 ++++++++++++++++++++
>   linux-user/aarch64/target_prctl.h    | 22 ++----------------
>   4 files changed, 63 insertions(+), 20 deletions(-)
>   create mode 100644 linux-user/aarch64/mte_user_helper.c
>   create mode 100644 linux-user/aarch64/mte_user_helper.h
>
> diff --git a/linux-user/aarch64/meson.build b/linux-user/aarch64/meson.build
> index 248c578d15..f75bb3cd75 100644
> --- a/linux-user/aarch64/meson.build
> +++ b/linux-user/aarch64/meson.build
> @@ -9,3 +9,5 @@ vdso_le_inc = gen_vdso.process('vdso-le.so',
>                                  extra_args: ['-r', '__kernel_rt_sigreturn'])
>   
>   linux_user_ss.add(when: 'TARGET_AARCH64', if_true: [vdso_be_inc, vdso_le_inc])
> +
> +linux_user_ss.add(when: 'TARGET_AARCH64', if_true: 
> [files('mte_user_helper.c')])
> diff --git a/linux-user/aarch64/mte_user_helper.c 
> b/linux-user/aarch64/mte_user_helper.c
> new file mode 100644
> index 0000000000..8be6deaf03
> --- /dev/null
> +++ b/linux-user/aarch64/mte_user_helper.c
> @@ -0,0 +1,34 @@
> +/*
> + * ARM MemTag convenience functions.
> + *
> + * This code is licensed under the GNU GPL v2 or later.
> + *
> + * SPDX-License-Identifier: LGPL-2.1-or-later
> + */
> +

  #include "qemu/osdep.h"
  #include "qemu.h"

> +#include <sys/prctl.h>
> +#include "mte_user_helper.h"
> +
> +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);
> +}
> diff --git a/linux-user/aarch64/mte_user_helper.h 
> b/linux-user/aarch64/mte_user_helper.h
> new file mode 100644
> index 0000000000..ee3f6b190a
> --- /dev/null
> +++ b/linux-user/aarch64/mte_user_helper.h
> @@ -0,0 +1,25 @@
> +/*
> + * ARM MemTag convenience functions.
> + *
> + * This code is licensed under the GNU GPL v2 or later.
> + *
> + * SPDX-License-Identifier: LGPL-2.1-or-later
> + */
> +
> +#ifndef AARCH64_MTE_USER_HELPER_H
> +#define AARCH64_MTE USER_HELPER_H
> +
> +#include "qemu/osdep.h"
> +#include "qemu.h"

NACK. See my comment on v5.