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

[Gustavo Romero <gustavo.romero@linaro.org>]

Hi Phil,

On 6/13/24 2:35 PM, Philippe Mathieu-Daudé wrote:
> 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.

Thanks, I forgot to add the inline hint and was really wondering if
I should add 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 */
>