Re: [PATCH 5/5] ARM: asm-source.exp link options in case of armv7b target

Victor Kamensky
2014-10-24T17:11:28Z

On 24 October 2014 01:52, Yao Qi <yao@codesourcery.com> wrote:
> 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.

I am not sure that I follow your argument, Your point that for
arm-linux-gnueab that has big endian multilib test will fail, and because
of that we want it to keep failing on armv7b-unknown-linux-gnueabihf
target? The fix I suggested will be activate only if target triplet
starts with 'armv7b'. The situation when target name starts
with 'armv7b' and has little endian multilib support seems very
hypothetical to me.

In case of arm-linux-gnueabi with big endian multilib pretty much
all tests will fail, unless caller will not specify correct compile/link
option (i.e compile -mbig-endian -Wl,--be8, link --be8, etc).

OK, it seems that the patch causes too much controversy, I am
going to drop it. I'll re-post series without it with final version of
other 3 patches, the one that I believe approved by you. And I
will wait for few days for additional feedback.

Thanks,
Victor

> --
> Yao (齐尧)