Re: [PATCH v2 05/29] LoongArch: KVM: Add vcpu related header files

[Paolo Bonzini]

On 2/21/23 07:46, maobibo wrote:
> > > +       asm volatile (
> > > +               "parse_r __reg, %[val]\n\t"
> > > +               ".word 0x5 << 24 | %[reg] << 10 | 0 << 5 | __reg\n\t"
> > Don't do this.  You should add the instruction to binutils first, then
> > make CONFIG_KVM depend on the assembler supporting this instruction.
> > This is completely unreadable and only fine for an internal PoC.
> We are preparing to submit these instruction support for binutils,
> however it is still necessary. Supposing that it is supported in future
> gcc version, we can not drop existing gcc 12/13 supporting to compiling
> kernel with LoongArch architecture.
>
> Maybe there will be human readable code like this:
> #if GCC_SUPPORT_KVM_INSTR
>    ...
> #else
>    asm volatile (".word   "
>    ...
> #endif

I agree, just add a comment with what would be the assembly code, i.e. 
something like

	/* Instructions only available in binutils v.... or later */
	asm volatile (
               "parse_r __reg, %[val]\n\t"
	       /* instrname %[val], %[reg] */
               ".word 0x5 << 24 | %[reg] << 10 | 0 << 5 | __reg\n\t"

Paolo