Re: [Swarm-Support] Re: Swarm 2.2 on Intel (and PPC) Mac OSX Tiger

[Bill Northcott]

On 24/07/2006, at 2:26 AM, Scott Christley wrote:

> GCC isn't deprecating nested functions as far as I know.  Apple  
> just disables their use within Xcode by passing a flag to the  
> compiler, this started with Xcode 2.2.  Supposedly you can re- 
> enable support with an additional compiler flag; however they  
> discourage it.  They mention some security feature but don't say  
> exactly what.

> On Jul 23, 2006, at 12:15 AM, Marcus G. Daniels wrote:
> > What compilers usually do to get an executable stack is to arrange  
> > to get it on a case by case basis using mprotect(2).  E.g. see  
> > these messages:
> >
> > http://gcc.gnu.org/ml/gcc-help/2005-12/msg00174.html
> > http://gcc.gnu.org/ml/gcc-help/2005-12/msg00177.html
> >
> > I was under the impression that this problem was just a regression  
> > in GCC.
> > Is there a later archived discussion and/or Bugzilla documentation  
> > of this deprecation?

I had seen the messages Marcus mentioned and chased it around a bit  
more.  As I understand it, this is a feature not a bug.  As explained  
in the messages, the operation of nested functions requires execution  
of code from the stack.  Allowing this is the sort of thing that  
hoary old mainframe types regard with horror as a nasty security  
vulnerability.  I think the intention is that somewhere down the  
track, it will be disabled at a very low level, possibly in hardware.

Apple decided to take a hard line to help ensure that code did not  
break on future hardware, the FSF decided to remain  more permissive  
for now and did not accept Apple's default.  Having said this, it  
seems to me to be a good idea to eradicate them now from the Swarm  
code base rather than wait until something breaks.

Bill Northcott