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From: Segher Boessenkool <segher@kernel.crashing.org>
Subject: Re: Saving to 32 bits of GPRs in signal context
Date: Wed, 30 May 2007 14:36:31 +0200
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: linuxppc-dev list <linuxppc-dev@ozlabs.org>,
	Steve Munroe <sjmunroe@us.ibm.com>,
	Ulrich Weigand <Ulrich.Weigand@de.ibm.com>,
	Paul Mackerras <paulus@samba.org>, Anton Blanchard <anton@samba.org>
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>>> Actually, it's the opposite... the prctl becomes a problem if you
>> have
>>> libs wanting to use 64 bits for optims
>>
>> The host application, or the dynamic loader, can call
>> the prctl() when it loads the DSO that needs it.
>
> Provided you know it does... and with static binaries it gets harder...

A mechanism like what is done for executable stacks
can be used, so you end up with something in the ELF
headers that tells you.  Not that I like this particular
mechanism.

>> In almost all cases this should all be transparent
>> for the user IMHO, based on some ELF flag.
>
> You reckon ? I was wondering about that ... maybe we should define some
> ELF personality for that ...
>
> But that means that existing programs wouldn't get it even while some
> libs they depend on might have such optims without the program knowing
> about it ...

Like I said, the dynamic loader should do the work
in such cases.

> Also, if I can avoid changing glibc ... (you know how hard it is !)

No really?  Tell me about it?  :-)


Segher