Re: [PATCH -v5 04/17] x86/alternatives: Add and use text_gen_insn() helper

[Steven Rostedt]

On Mon, 11 Nov 2019 14:12:56 +0100
Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:

> +void *text_gen_insn(u8 opcode, const void *addr, const void *dest)
> +{
> +	static union text_poke_insn insn; /* text_mutex */
> +	int size = 0;
> +
> +	lockdep_assert_held(&text_mutex);
> +
> +	insn.opcode = opcode;
> +
> +#define __CASE(insn)	\
> +	case insn##_INSN_OPCODE: size = insn##_INSN_SIZE; break
> +
> +	switch(opcode) {
> +	__CASE(INT3);
> +	__CASE(CALL);
> +	__CASE(JMP32);
> +	__CASE(JMP8);
> +	}
> +
> +	if (size > 1) {
> +		insn.disp = (long)dest - (long)(addr + size);
> +		if (size == 2)

Could we add a comment here. It took me a little bit to figure out why
you have this BUG_ON().

-- Steve


> +			BUG_ON((insn.disp >> 31) != (insn.disp >> 7));
> +	}
> +
> +	return &insn.text;
> +}