Re: [PATCH] S390: Hotpatching fixes.

[Jakub Jelinek <jakub@redhat.com>]

On Fri, Mar 27, 2015 at 10:30:38AM +0100, Andreas Krebbel wrote:
> At a second glance it is not really clear to me why we disable hotpatching for nested functions at
> all. While it is probably a bit difficult to actually hotpatch them I don't see why we should
> prevent it. We probably just copied that over from the x86 ms_hook_prologue attribute implementation:
> 
> static bool
> ix86_function_ms_hook_prologue (const_tree fn)
> {
>   if (fn && lookup_attribute ("ms_hook_prologue", DECL_ATTRIBUTES (fn)))
>     {
>       if (decl_function_context (fn) != NULL_TREE)
> 	error_at (DECL_SOURCE_LOCATION (fn),
> 		  "ms_hook_prologue is not compatible with nested function");
>       else
>         return true;
>     }
>   return false;
> }
> 
> Also the kernel guys (one of the main users of that feature) confirmed that they in principle prefer
> hotpatching to behave more like -pg and -pg does insert an mcount call for nested functions.
> (Although I would be surprised to hear of nested functions in the Linux kernel).
> 
> So I'm inclined to just remove that special handling of nested functions.

Agreed, I also wondered what would be so special about nested functions
here.
Sure, one could hotpatch them with code clobbering the static chain
register, but that wouldn't be a gcc issue.

	Jakub