Re: [PATCH] LoongArch: Fix and simplify fcsr initialization on execve

[Xi Ruoyao]

On Tue, 2024-01-02 at 10:35 +0800, Huacai Chen wrote:

/* snip */

> > The only other architecture setting FCSR in SET_PERSONALITY2 is MIPS.
> > They do this for supporting different FP flavors (NaN encodings etc).
> > which do not exist on LoongArch.  I'm not sure how MIPS evades the issue
> > (or maybe it's just buggy too) as I don't have a running MIPS hardware
> > now.
> I think you can use QEMU. :)

I'll investigate it later.

> > So for LoongArch, just remove the current->thread.fpu.fcsr setting from
> > SET_PERSONALITY2 and do it in start_thread, after lose_fpu(0).  And we
> > just set it to 0, instead of boot_cpu_data.fpu_csr0 (because we should
> > provide the userspace a consistent configuration, no matter how hardware
> > and firmware behave).
> I still prefer to set fcsr to boot_cpu_data.fpu_csr0, because we will
> add LoongArch32 later, not sure whether something will change.

I just seen fpu_csr0 is initialized to FPU_CSR_RN which is just 0 for
LA64, so my concern about firmware & hardware leaving non-zero FCSR is
not valid.  I'll send v2 to keep using boot_cpu_data.fpu_csr0 then.

> 
> 
-- 
Xi Ruoyao <xry111@xxxxxxxxxxx>
School of Aerospace Science and Technology, Xidian University