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

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