linux-kernel - Re: RFC: binutils PATCH: Set e_type to ET

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Message-ID: <CAMe9rOr9L7OmdxGyzgiWuTTBXy4A+qUVa+3Mar+J_hE8H=rRZg@mail.gmail.com>
Date:	Tue, 10 Dec 2013 14:47:06 -0800
From:	"H.J. Lu" <hjl.tools@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>,
	Binutils <binutils@...rceware.org>
Subject: Re: RFC: binutils PATCH: Set e_type to ET_EXEC for -pie -Ttext-segment=

On Tue, Dec 10, 2013 at 2:36 PM, Alan Modra <amodra@...il.com> wrote:
> On Mon, Dec 09, 2013 at 07:10:23PM -0800, H.J. Lu wrote:
>> Linker sets e_type in ELF header to ET_DYN for -pie -Ttext-segment=0xXXX.
>> When I added -Ttext-segment=0xXXX, one goal was to load
>> small model executable above 4GB on Linux/x86-64, which
>> was done with -pie -Ttext-segment=0xXXX.  But -pie sets
>> e_type in ELF header to ET_DYN and kernel may ignore
>> p_vaddr in ELF header to load ET_DYN binary at a random
>> address.  This patch changes ld to set e_type in ELF header
>> to ET_EXEC if the first PT_LOAD segment has non-zero
>> p_vaddr.  If this is unacceptable as generic ELF change,
>> I can make it specific to x86.
>
> Well, I suppose it's a hack to use ET_DYN for executables in the first
> place, so one more hack in the linker hardly matters.  Why not just
> patch the kernel though?  The kernel can look at the first PT_LOAD
> header just as easily as the linker, and it's the kernel that is doing
> the loading after all.
>

Kernel should have some freedom on where to load ET_DYN object.
But when -Ttext-segment= is used, programmer expects the
executable will be loaded at the specified address.  Setting
ET_EXEC will guarantee that it will be loaded at that address.


-- 
H.J.
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