Re: [PATCH bpf v2 2/2] selftests/bpf: Check per-CPU address resolution per register

[Eduard Zingerman <eddyz87@gmail.com>]

On Fri, 2026-08-14 at 13:32 -0700, Vineet Gupta wrote:

...

> +/*
> + * An ld_imm64 of a per-CPU map value is followed by a mov_percpu_addr that
> + * reuses the same register, so the register the address lands in decides how
> + * the JIT encodes the add. On x86 R5, R7, R8 and R9 are the extended
> + * registers, whose high bit needs REX.R because the destination sits in
> + * ModRM.reg. Check one program per extended register, since getting the
> + * prefix wrong resolves the address into whichever register shares the low
> + * three bits instead.
> + */
> +
> +SEC("raw_tp")
> +__description("per-CPU address into r5")
> +__success
> +__arch_x86_64
> +__jited("	addq	%gs:{{.*}}, %r8")
> +__naked void percpu_addr_into_r5(void)
> +{
> +	asm volatile ("					\
> +	r5 = %[percpu_data] ll;				\
> +	r0 = *(u32 *)(r5 + 0);				\
> +	exit;						\
> +"	:
> +	: __imm_addr(percpu_data)
> +	: __clobber_all);
> +}

Thank you for adding the tests.
Maybe save some space by just packing it as a single test?

__jited("	addq	%gs:{{.*}}, %...")
__jited("	addq	%gs:{{.*}}, %...")
__jited("	addq	%gs:{{.*}}, %...")
__jited("	addq	%gs:{{.*}}, %...")
__jited("	addq	%gs:{{.*}}, %...")

	r0 = %[percpu_data] ll;				\
	r1 = %[percpu_data] ll;				\
	r2 = %[percpu_data] ll;				\
	r3 = %[percpu_data] ll;				\
	r4 = %[percpu_data] ll;				\
	r5 = %[percpu_data] ll;				\
	r6 = %[percpu_data] ll;				\
	r7 = %[percpu_data] ll;				\
	r8 = %[percpu_data] ll;				\
	r9 = %[percpu_data] ll;				\

More compact and no need to describe in length why only R{5,7,8,9} are selected.

...