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Re: [PATCH 5/5] ARM: asm-source.exp link options in case of armv7b target
- From: Yao Qi <yao at codesourcery dot com>
- To: Andrew Pinski <pinskia at gmail dot com>
- Cc: Victor Kamensky <victor dot kamensky at linaro dot org>, "gdb-patches at sourceware dot org" <gdb-patches at sourceware dot org>
- Date: Fri, 24 Oct 2014 16:52:24 +0800
- Subject: Re: [PATCH 5/5] ARM: asm-source.exp link options in case of armv7b target
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- References: <1413853021-4393-1-git-send-email-victor dot kamensky at linaro dot org> <1413853021-4393-6-git-send-email-victor dot kamensky at linaro dot org> <87siievw6z dot fsf at codesourcery dot com> <CAA3XUr3eDYiCAG3rSwn_4kR2gW7UsPBB++KLBFZvMgg3qOb4cw at mail dot gmail dot com> <CA+=Sn1n2e+j_FX34ymZTM24ART=W65nwk31ijTv1-Hn3vpJyBQ at mail dot gmail dot com>
Andrew Pinski <pinskia@gmail.com> writes:
>> Any executable/library that runs on big endian V7 *must* be linked
>> with -be8 option. Otherwise it simply won't run. In any other multilib
>> option vfp, neon, etc -be8 must be set. Basically, in big endian case
>> gcc/gas generates data and instructions in big endian
>> format but ARM V7 requires that instruction should be little endian
>> format. It is linker that does instructions byte swap. If -be8 flag
>> is not passed during link while running on ARM V7 big endian target
>> executable with crash with SIGILL. If link happens through gcc, then
>> -be8 always passed for non relocatable code by compiler. In this
>> particular case link happens directly with linker and -be8 is not
>> default, so it is needed. One may argue that -be8 for final
>> executables in ARM V7 BE target should be default even for
>> linker, but it is not the current case ...
>>
>> Also note that you have plenty examples in the same test
>> gdb/testsuite/gdb.asm/asm-source.exp
>> that do very similar things. For example:
>>
>> "powerpc64le-*" {
>> set asm-arch powerpc64le
>> set asm-flags "-a64 -I${srcdir}/${subdir} $obj_include"
>> append link-flags " -m elf64lppc"
>> }
>>
>> Why "-m elf64lppc" is set for powerpc64le target? I suspect
>> by very similar reasons.
>
>
> Yes and no. For PowerPC64 little-endian is Linux only so it will
> never have a multi-libs that support both little-endian and
> big-endian. While for arm*-*-*, you can have a bare metal env and
> that could have a multi-lib for both little and big endian.
Andrew is right. We can have a arm-linux-gnueabi toolchain which has
multilibs for the combination of {le, be} x {armv7, armv6, armv5}, and
this test still fails on armv7 be multilib.
--
Yao (éå)