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Date: Wed, 11 Jul 2007 11:02:57 +1000
From: Paul Mackerras <paulus@samba.org>
To: Segher Boessenkool <segher@kernel.crashing.org>
Subject: Re: [PATCH] Allow exec on 32-bit from readable, non-exec pages,
	with a warning.
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Cc: linuxppc-dev@ozlabs.org, Arnd Bergmann <arnd@arndb.de>
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Segher Boessenkool writes:

> >> Yeah.  Giving the warning is a good thing though.
> >
> > No, it isn't; it's just noise, if we're not ever going to do anything
> > to prevent the behaviour - and we can't.
> 
> The same userland code will not run correctly on PPC64 or BookE
> systems.  Is that not a reason to warn?

It *will* run on ppc64 systems, because there we get the
READ_IMPLIES_EXEC personality flag set via the elf_read_implies_exec
thing in include/asm-powerpc/elf.h.  The READ_IMPLIES_EXEC flag is
only set if we don't have the non-executable stack note in the ELF
header, i.e. only for old binaries or libraries.

As for Book E, that could be fixed using elf_read_implies_exec too, if
anyone cared.  In fact maybe the correct solution is to have

#define elf_read_implies_exec(ex, exec_stk) \
	(exec_stk != EXSTACK_DISABLE_X) : 0)

for all 32-bit powerpc.

Paul.