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SH FDPIC ABI spec/binutils and kernel conflict on flag definitions
- From: Rich Felker <dalias at libc dot org>
- To: linux-sh at vger dot kernel dot org, binutils at sourceware dot org
- Cc: Oleg Endo <oleg dot endo at t-online dot de>
- Date: Wed, 9 Sep 2015 23:34:00 -0400
- Subject: SH FDPIC ABI spec/binutils and kernel conflict on flag definitions
- Authentication-results: sourceware.org; auth=none
In the ELF Header part of the SH FDPIC ABI document, it's stated that
EF_SH_FDPIC|EF_SH_PIC means each LOAD segment can be independently
positioned, while EF_SH_FDPIC by itself (without EF_SH_PIC) means the
relative position of LOAD segments with respect to each other is fixed
(like in normal ELF usage). This seems to match what binutils outputs.
However the kernel contains the code (arch/sh/include/asm/elf.h):
#define elf_check_const_displacement(x) ((x)->e_flags & EF_SH_PIC)
exec_params.flags |= ELF_FDPIC_FLAG_CONSTDISP;
which does exactly the opposite: the presence of the EF_SH_PIC flag,
rather than absence of it, causes the kernel to treat the binary as
one requiring "constant displacement" between LOAD segments.
If my analysis is correct, how should this be fixed? It seems to me
the kernel is clearly wrong, but it might also be considered the de
facto ABI. Is there any way forward that allows fixing this bug (which
defeats the whole purpose of FDPIC) without breaking existing usage?
Or is there no existing usage to care about?