Re: [Minios-devel] [UNIKRAFT RFC PATCH 2/5] plat/kvm: arm64: Enable the fp/simd at the starting point

[Santiago Pagani <Santiago.Pagani@xxxxxxxxx>]

Hi Julien,

Yes, you are right.

How about asking Justin to place a couple of TODOs about these issues and 
fixing them in January?  I'm just concerned about delaying this longer, as not 
having floating point on ARM is currently blocking several things (i.e., 
porting of C++ to ARM64, porting of our machine learning acceleration framework 
to ARM64, porting of the ARM compute library to ARM64, porting of the LGVL 
library to ARM64, finalizing a WAMR on Raspberry Pi 3 demo, etc.).

Best,
Santiago

On 20.12.19, 09:11, "Minios-devel on behalf of Julien Grall" 
<minios-devel-bounces@xxxxxxxxxxxxxxxxxxxx on behalf of julien@xxxxxxx> wrote:

    
    
    On 20/12/2019 08:04, Santiago Pagani wrote:
    
    Hi,
    
    May I ask to avoid top-posting? This makes the conversation fairly 
    difficult to read.
    
    > Actually, the comment is wrong. Setting those two bits in cpacr_el1 does 
not enable fp/simd, but actually disables traps for floating point and SIMD 
instructions both in EL0 and EL1.
    > The actually enabling of floating point and SIMD instructions is done by 
your other patch that removes the -mgeneral-regs-only flag.
    > Therefore, there is no harm in doing that in the kernel when floating 
point is enabled. I would however fix the comment though.
    
    Not quite, you make your life so much more difficult if your kernel 
    should not use FPSIMD registers and will use them (see my other answer).
    
    So for safety, it is better to keep trapping FPSIMD if they are not 
    meant to be used. This is likely to avoid you a lot of debugging in the 
    future if FPSIMD are misused.
    
    Cheers,
    
    -- 
    Julien Grall
    
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