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From: Roland McGrath <roland@hack.frob.com>
To: Szabolcs Nagy <szabolcs.nagy@arm.com>
Cc: <nd@arm.com>,
    Renlin Li <renlin.li@foss.arm.com>,
    <libc-alpha@sourceware.org>,
    Marcus Shawcroft <Marcus.Shawcroft@arm.com>,
    Richard Earnshaw <Richard.Earnshaw@arm.com>
Subject: Re: [GLIBC][AARCH64]Rewrite elf_machine_load_address using _DYNAMIC
 symbol
In-Reply-To: Szabolcs Nagy's message of  Wednesday, 9 November 2016 14:48:21 +0000 <58233735.2050204@arm.com>
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Date: Wed, 09 Nov 2016 22:02:00 -0000
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> On 08/11/16 21:28, Roland McGrath wrote:
> > Show me the code you have in mind using _DYNAMIC.  The scheme using a
> > linker-defined symbol with value 0 is the only one I'm aware of that
> > reduces to the minimal number of assembly instructions, with none of them
> > being a load.
> 
> well the current x86_64 code is already doing what i had in mind.

And it is more costly than using _BASE.

> i assumed GOT[0] is used elsewhere so it has to be computed anyway
> and then doing (_DYNAMIC-GOT[0]) should be the same as _BASE using
> an extra sub.

Of course all the methods that work get the same result!
The point is that the _BASE method does it the most efficiently.