Re: [PATCH 12/15] x86/static_call: Add out-of-line static call implementation

[Peter Zijlstra]

On Fri, Jun 07, 2019 at 10:38:46AM +0200, Peter Zijlstra wrote:
> On Fri, Jun 07, 2019 at 06:13:58AM +0000, Nadav Amit wrote:
> > > On Jun 5, 2019, at 6:08 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> 
> > > +void arch_static_call_transform(void *site, void *tramp, void *func)
> > > +{
> > > +	unsigned char opcodes[CALL_INSN_SIZE];
> > > +	unsigned char insn_opcode;
> > > +	unsigned long insn;
> > > +	s32 dest_relative;
> > > +
> > > +	mutex_lock(&text_mutex);
> > > +
> > > +	insn = (unsigned long)tramp;
> > > +
> > > +	insn_opcode = *(unsigned char *)insn;
> > > +	if (insn_opcode != 0xE9) {
> > > +		WARN_ONCE(1, "unexpected static call insn opcode 0x%x at %pS",
> > > +			  insn_opcode, (void *)insn);
> > > +		goto unlock;
> > 
> > This might happen if a kprobe is installed on the call, no?
> > 
> > I donât know if you want to be more gentle handling of this case (or perhaps
> > modify can_probe() to prevent such a case).
> > 
> 
> yuck.. yes, that's something that needs consideration.

For jump_label this is avoided by jump_label_text_reserved(), I'm
thinking static_call should do the same.