Re: RFC: binutils PATCH: Set e_type to ET_EXEC for -pie -Ttext-segment=0xXXX

["H. Peter Anvin" <hpa at zytor dot com>]

Where do the _32 and _32S relocations come from?  Are we mixing multiple things inside -pie?

"H.J. Lu" <hjl.tools@gmail.com> wrote:
>On Mon, Dec 9, 2013 at 7:23 PM, H. Peter Anvin <hpa@zytor.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@gnu-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@gnu-6 tmp]$ gcc -fpie -pie  a.c -Wl,-Ttext-segment=0x7ff000000
>[hjl@gnu-6 tmp]$
>
>
>---
>H.J.

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