Re: [PATCH] Makerules: pass CFLAGS when building .S files, BZ #23273

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 11/06/2018 10:22, Florian Weimer wrote:
> On 06/11/2018 03:18 PM, Sergei Trofimovich wrote:
>> On Mon, 11 Jun 2018 14:50:24 +0200
>> Florian Weimer <fweimer@redhat.com> wrote:
>>
>>> On 06/11/2018 02:35 PM, Sergei Trofimovich wrote:
>>>> On Mon, 11 Jun 2018 08:17:37 -0300
>>>> Adhemerval Zanella <adhemerval.zanella@linaro.org> wrote:
>>>>   
>>>>> On 11/06/2018 07:46, Florian Weimer wrote:
>>>>>> On 06/11/2018 12:28 PM, Sergei Trofimovich wrote:
>>>>>>> When glibc is built on armv7 with CFLAGS="-pipe -march=armv7-a -O2 -mfpu=neon"
>>>>>>> rtld fails to link due to missing memcpy symbol.
>>>>>>>
>>>>>>> This happens because .c files are built with -mfpu=neon flag but .S/.s files
>>>>>>> are built without it. Among other things -mfpu=neon defines __ARM_NEON__.
>>>>>>>
>>>>>>> To fix this mismatch CFLAGS should be passed consistently to .c and .S files.
>>>>>>
>>>>>> Please check if you can fix this by putting the architecture selection flags into the CC and CXX variables when invoking configure.
>>>>
>>>> I'm not sure just adding an arch flag is enough:
>>>>       https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/arm/armv7/multiarch/memcpy_neon.S;h=1a8d8bbe9e128618105be0652de42a34fbc52d73;hb=HEAD
>>>>      ...
>>>>      2 #ifndef __ARM_NEON__
>>>>      3 # define memcpy __memcpy_neon
>>>> Here memcpy_neon.S explicitly supports both neon-enabled and disabled flags.
>>>
>>> Does this mean your proposed patch fails to address the issue, too?
>>
>> My proposed patch fixes ld.so linkage (and ld.so seems to work).
> 
> Yes, but what about using CC/CXX setting at configure time to achieve the same effect?

It works as expected by using the flags on CC/CXX:

  1. For only '-march=armv7-a' sysdeps/arm/armv7/multiarch/rtld-memcpy.S will be used
     and it will redirect to use sysdeps/arm/armv7/multiarch/rtld-memcpy.S.

  2. For '-march=armv7-a -mfpu=neon' string/memcpy.os will be empty which will force
     librtld.map to point to memcpy_neon.os to be used as the linker implementation
     (which creates the rtld-memcpy_neon.os).

Now the question is whether we should support the same behaviour with the ABI options
set only in CFLAGS instead.

NOTE: from previous discussion it seems armv7-a should imply NEON, so I think 1. should
behave as 2. which means I think we should test for __ARM_ARCH == 7 instead of __ARM_NEON__.