[PING^3] Re: [PATCH 1/3] Support instrumenting returns of instrumented functions

[Jan Hubicka]

> On Wed, Nov 28, 2018 at 04:59:25PM +0100, Jan Hubicka wrote:
> > Hi,
> > I wonder how __return_loc sections work.  In general it would be nice to
> 
> You mean how it's used? It's for patching in/out return instrumentation
> at runtime, and to find them we use the sections.
> 
> > avoid direct output of assembler code in favour of adding instructions
> > to rtl stream which should be possible to insert the call and return.
> 
> That would be a full rewrite how all these hooks work. I was 
> hoping extending the existing frame work would be good enough for now.

Yep, it is ugly and it hits us ocassionaly as with the CET
instrumentation, but I suppose we should care about this in stage1.
> 
> > __return_loc seems harder, also I wonder if it makes unwind information
> > possible?
> 
> Do we need unwind information for calls? I thought it was only
> for other stack manipulation.

I just wonder if backtraces are right if something triggers in the extra
code.  If you make control flow to jump into separate section, I suppose
backtraces won't be right.  Not sure if that is necessarily issue?

Honza
> 
> -Andi