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Re: RFC: binutils PATCH: Set e_type to ET_EXEC for -pie -Ttext-segment=
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: LKML <linux-kernel at vger dot kernel dot org>, Binutils <binutils at sourceware dot org>
- Date: Thu, 12 Dec 2013 07:42:24 -0800
- Subject: Re: RFC: binutils PATCH: Set e_type to ET_EXEC for -pie -Ttext-segment=
- Authentication-results: sourceware.org; auth=none
- References: <CAMe9rOob2T+VWkZyHpaoBy6fUeTyAocpw4-cBpdrar2rtdAeew at mail dot gmail dot com> <20131210223615 dot GA10239 at bubble dot grove dot modra dot org> <CAMe9rOr9L7OmdxGyzgiWuTTBXy4A+qUVa+3Mar+J_hE8H=rRZg at mail dot gmail dot com>
On Tue, Dec 10, 2013 at 2:47 PM, H.J. Lu <email@example.com> wrote:
> On Tue, Dec 10, 2013 at 2:36 PM, Alan Modra <firstname.lastname@example.org> 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.
I checked it in with 2 testcases.