Luca Dariz, le mer. 01 mars 2023 18:40:37 +0100, a ecrit:
> + asm volatile("wrmsr"
> + :
> + : "c" (regaddr), "a" (low), "d" (high)
> + : "memory" /* wrmsr is a serializing instruction */
The comment could be misleading.
The fact that it's a serialization instruction does not *require* to
express it to the compiler.
But the fact that wrmsr needs to be a serialization instruction (because
it may depend on other writes etc.) means that one *also* wants to make
the asm snippet serialized by the compiler thanks to the memory clobber.
So I'd rather see:
: "memory" /* wrmsr usage needs serialization */
> + /* avoid leaking information in callee-clobbered registers */
> + xorq $0,%rdi
> + xorq $0,%rsi
> + xorq $0,%rdx
> + xorq $0,%r10
> + xorq $0,%r9
> + xorq $0,%r8
No, that's a no-op :)
> + xorq %rdi,%rdi
etc.
Samuel
