Re: [PATCH 3/6] linux-user: Add code for PR_GET/SET_UNALIGN

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

On 8/1/24 22:13, Richard Henderson wrote:
> On 1/9/24 04:15, Philippe Mathieu-Daudé wrote:
>>> +/*
>>> + * This can't go in hw/core/cpu.c because that file is compiled only
>>> + * once for both user-mode and system builds.
>>> + */
>>>   static Property cpu_common_props[] = {
>>> -#ifndef CONFIG_USER_ONLY
>>> +#ifdef CONFIG_USER_ONLY
>>>       /*
>>> -     * Create a memory property for softmmu CPU object,
>>> -     * so users can wire up its memory. (This can't go in hw/core/cpu.c
>>> -     * because that file is compiled only once for both user-mode
>>> -     * and system builds.) The default if no link is set up is to use
>>> +     * Create a property for the user-only object, so users can
>>> +     * adjust prctl(PR_SET_UNALIGN) from the command-line.
>>
>> How can I test this per-thread property?
> 
> -cpu foo,prctl-unalign-sigbus=true
> 
> 
>> Shouldn't this be an accel (TCG/user) property, for all threads?
> 
> There is always one cpu at user-only startup, and it is copied on clone.
> 
> Logically it would be a kernel property, since it's something the kernel 
> does, not the cpu.  But cpu vs accel makes no difference to me; it was 
> just easy here.

Can a process started with prctl(PR_SET_UNALIGN) unset it before
forking?

"kernel property" as "accel property" works for me.

> IIRC, this is simply a proxy for not really being able to inherit this 
> bit across fork+exec like you can with the real kernel.
> 
> 
> r~