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Re: [PATCH] Ensure that MIPS target code is compiled for the O32 ABI.

From: Andrei Borzenkov
Subject: Re: [PATCH] Ensure that MIPS target code is compiled for the O32 ABI.
Date: Sun, 13 Sep 2015 17:10:37 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0

13.09.2015 05:41, Mark H Weaver пишет:
Andrei Borzenkov <address@hidden> writes:

ld: /tmp/conftest-efc530.o: compiled for a big endian system and target is 
little endian
ld: /tmp/conftest-efc530.o: endianness incompatible with that of the selected 

This is the same problem we had on powerpc. Your binutils are set to
use little-endian output by default; we need to explicitly enable
either big or little endian in this case as well. Could you try
attached patch to verify?

I'm glad to report that with your new patch, GRUB successfully builds on
GuixSD mips64el with TARGET_CC=clang.  I haven't yet tried booting it

Did you have chance to test whether compiled grub actually work?

Your patch works for me with gcc, although config.log shows this warning
when building the test program in your new code with the correct flags
for gcc (-mabi=32):

    ld: warning: cannot find entry symbol __start; defaulting to 

Well, I just reused existing checks in this case; we worry about it later.

Okay.  I guess the name of the start symbol depends on the platform and
linker.  E.g. boot/mips/loongson/fwstart.S has this:

--8<---------------cut here---------------start------------->8---
        .global start,_start,__start
--8<---------------cut here---------------end--------------->8---

Other platforms have only '_start', or both 'start' and '_start'.

I also worry that linking an O32 executable might be fragile on a pure
non-multilib N32 system such as GNU Guix, where we lack even the gcc
runtime library (libgcc_s) for O32.  For now it seems to work, but I
wonder if it might be more robust to do the test compilation with -c and

It is using -nostdlib; is it not enough?

The warning above makes me doubt the portability and future-proofness of
the link step of this test.  This problem could be avoided entirely by
omitting the link step.  The link step serves no purpose in this test,
and is a potential source of portability problems.

This step helped us to catch endianness mismatch; we want to ensure in this case that full toolchain works to produce final binary.

Having said that, if you prefer to keep the link step, I guess it will
probably be okay in practice to define 'start', '_start', and '__start'
as above.  Do as you think best.

Please test two attached patches. They separate o32 test from endianness test. I compile-tested them using cross-binutils for mips and powerpc64le to compile for mipsel and powerpc. The first patch also adds additional _start and __start symbols to endianness tests to avoid compiler warnings.

I am interested in both native and cross compilation - i.e. please test for both --target=mipsel and --target=mips both with gcc and clang. config.log from all runs would be interesting even for successful cases.

Attachment: 0001-configure-try-to-find-options-to-force-endian-on-MIP.patch
Description: Text Data

Attachment: 0002-configure-try-to-force-o32-ABI-on-MIPS.patch
Description: Text Data

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