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

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Date:	Tue, 10 Dec 2013 04:20:58 -0800
From:	"H.J. Lu" <hjl.tools@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Binutils <binutils@...rceware.org>, Jiri Kosina <jkosina@...e.cz>,
	LKML <linux-kernel@...r.kernel.org>,
	Josh Boyer <jwboyer@...hat.com>
Subject: Re: RFC: binutils PATCH: Set e_type to ET_EXEC for -pie -Ttext-segment=

On Mon, Dec 9, 2013 at 8:57 PM, H. Peter Anvin <hpa@...or.com> wrote:
> Where do the _32 and _32S relocations come from?  Are we mixing multiple things inside -pie?

They come from crt1.o and crtbegin.o.  -pie uses Scrt1.o and crtbeginS.o.

> "H.J. Lu" <hjl.tools@...il.com> wrote:
>>On Mon, Dec 9, 2013 at 7:23 PM, H. Peter Anvin <hpa@...or.com> wrote:
>>> On 12/09/2013 07:05 PM, H.J. Lu wrote:
>>>>>
>>>>> I see.  Maybe linker can set ET_EXEC if vaddr is non-zero.
>>>>>
>>>>
>>>> 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.
>>>>
>>>
>>> Why not just drop the -pie from the command line?  I would expect
>>-pie
>>> to set ET_DYN, but if you want to load at a specific address one
>>would
>>> expect to use -Ttext-segment=... and *not* -pie.
>>>
>>
>>No.  We must keep -pie.  Without -pie, we can't set -Ttext-segment=
>>to above 4GB:
>>
>>[hjl@...-6 tmp]$ gcc  a.c -Wl,-Ttext-segment=0x7ff000000
>>/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../lib64/crt1.o: In
>>function `_start':
>>(.text+0x12): relocation truncated to fit: R_X86_64_32S against symbol
>>`__libc_csu_fini' defined in .text section in
>>/usr/lib64/libc_nonshared.a(elf-init.oS)
>>/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../lib64/crt1.o: In
>>function `_start':
>>(.text+0x19): relocation truncated to fit: R_X86_64_32S against symbol
>>`__libc_csu_init' defined in .text section in
>>/usr/lib64/libc_nonshared.a(elf-init.oS)
>>/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../lib64/crt1.o: In
>>function `_start':
>>(.text+0x20): relocation truncated to fit: R_X86_64_32S against symbol
>>`main' defined in .text section in /tmp/ccV9AIMR.o
>>/usr/lib/gcc/x86_64-redhat-linux/4.8.2/crtbegin.o: In function
>>`deregister_tm_clones':
>>crtstuff.c:(.text+0x1): relocation truncated to fit: R_X86_64_32
>>against symbol `__TMC_END__' defined in .data section in a.out
>>crtstuff.c:(.text+0x8): relocation truncated to fit: R_X86_64_32S
>>against `.tm_clone_table'
>>crtstuff.c:(.text+0x23): relocation truncated to fit: R_X86_64_32
>>against `.tm_clone_table'
>>/usr/lib/gcc/x86_64-redhat-linux/4.8.2/crtbegin.o: In function
>>`register_tm_clones':
>>crtstuff.c:(.text+0x31): relocation truncated to fit: R_X86_64_32
>>against symbol `__TMC_END__' defined in .data section in a.out
>>crtstuff.c:(.text+0x38): relocation truncated to fit: R_X86_64_32S
>>against `.tm_clone_table'
>>crtstuff.c:(.text+0x63): relocation truncated to fit: R_X86_64_32
>>against `.tm_clone_table'
>>/usr/lib/gcc/x86_64-redhat-linux/4.8.2/crtbegin.o: In function
>>`frame_dummy':
>>crtstuff.c:(.text+0xa6): relocation truncated to fit: R_X86_64_32
>>against `.jcr'
>>/tmp/ccV9AIMR.o: In function `main':
>>a.c:(.text+0x5): additional relocation overflows omitted from the
>>output
>>collect2: error: ld returned 1 exit status
>>[hjl@...-6 tmp]$ gcc -fpie -pie  a.c -Wl,-Ttext-segment=0x7ff000000
>>[hjl@...-6 tmp]$
>>
>

-- 
H.J.
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