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GNAT, executable stack and trampolines (was: Next version of libtemplates-parser in Debian)

Reto Buerki wrote:
> Actually these cases are not so rare. As soon as you use Ada.Containers
> you are almost there. 'Access to a nested function is enough. The
> following code illustrates this:

Thanks for the nice reproducer.

[...]
> The stack of the resulting binary is executable:
> 
> GNU_STACK      0x0000000000000000 0x0000000000000000 0x0000000000000000
>                  0x0000000000000000 0x0000000000000000  RWE    8
> 
> Tested with gnat in Lenny, Squeeze and sid (amd64/i386).
> 
> It's interesting that the same code compiled with GNAT GPL 2010 does not
> result in an executable stack:
> 
> GNU_STACK      0x0000000000000000 0x0000000000000000 0x0000000000000000
>                  0x0000000000000000 0x0000000000000000  RW     8
> 
> Since an executable stack is not very nice I think it would be
> interesting if we could identify the patch which is responsible for this
> behavior. Maybe we could port it to work with 4.6.0.

AFAICT, there are several:

2008-05-28 Eric Botcazou <ebotcazou@adacore.com>

	* system-lynxos-ppc.ads (Always_Compatible_Rep): Set to False.
	* system-lynxos-x86.ads (Always_Compatible_Rep): Set to False. 

2008-05-27  Bob Duff  <duff@adacore.com>

         * gnat_rm.texi:
         Document the new behavior regarding trampolines.

2008-05-27 Eric Botcazou <ebotcazou@adacore.com>
	
	* system-darwin-ppc.ads (Always_Compatible_Rep): Set to False.
	* system-darwin-x86.ads (Always_Compatible_Rep): Likewise.
	* system-freebsd-x86.ads (Always_Compatible_Rep): Likewise.
	* system-linux-ppc.ads (Always_Compatible_Rep): Likewise.
	* system-linux-x86_64.ads (Always_Compatible_Rep): Likewise.
	* system-linux-x86.ads (Always_Compatible_Rep): Likewise.
	* system-mingw.ads (Always_Compatible_Rep): Likewise.
	* system-solaris-sparc.ads (Always_Compatible_Rep): Likewise.
	* system-solaris-sparcv9.ads (Always_Compatible_Rep): Likewise.
	* system-solaris-x86.ads (Always_Compatible_Rep): Likewise. 

2008-05-25 Eric Botcazou <ebotcazou@adacore.com>

	* trans.c (Attribute_to_gnu) <Code_Address>: Set TREE_NO_TRAMPOLINE
	instead of TREE_STATIC on the ADDR_EXPR.

All these patches are already in gnat-4.4 because the commits took place
during Stage 1 of the GCC 4.4 cycle, so your results for Squeeze and sid
surprise me.  Anyway, I anticipate that the stack will not be executable
with gnat-4.6, just like with GNAT GPL 2010.

-- 
Ludovic Brenta.
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