Re: c-ares linking problem on Apple, cross-compiling for ARM.

From: Daniel F via curl-library <curl-library_at_lists.haxx.se>
Date: Wed, 25 Jan 2023 16:52:18 +0100

W dniu 2023-01-25 15:54, Jeffrey Walton via curl-library napisał(a):
> On Wed, Jan 25, 2023 at 9:37 AM Ben Greear <greearb_at_candelatech.com>
> wrote:
>>
>> On 1/25/23 3:51 AM, Jeffrey Walton wrote:
>> > On Wed, Jan 25, 2023 at 12:46 AM Ben Greear via curl-library
>> > <curl-library_at_lists.haxx.se> wrote:
>> >>
>> >> So, I'm well off in the weeds here.
>> >>
>> >> Trying to compile lib-cares on macos (using clang), for ARM target on x86-64 macos machine. I'm able to see the
>> >> c files compiled for the right target, but the linker part is not passing the -target
>> >> flag it seems.
>> >>
>> >> [...]
>> >> Here is how I am doing the configure step:
>> >>
>> >> (cd c-ares.ct && \
>> >> export CFLAGS="-mmacosx-version-min=11.0 -target arm64-apple-macos11"; \
>> >> export LDFLAGS="-mmacosx-version-min=11.0 -target arm64-apple-macos11"; \
>> >> ./configure --enable-warnings --host=aarch64-apple-darwin && \
>> >> perl -i.bkp -pe 's/^archive_cmds.*\K-install_name/-target arm64-apple-macos11 -install_name/' libtool)
>> >
>> > I think there may be two problems. First, I think you should set a
>> > sysroot. Second, I think you should set CPPFLAGS. I would also set
>> > CXXFLAGS for completeness, but I don't believe it's a problem in this
>> > instance. CXXFLAGS will just be ignored if it is not used.
>> >
>> > CPPFLAGS will include --isysroot . LDFLAGS will include --sysroot.
>> >
>> > Here's what things look like when I set a cross-compile environment
>> > for an iPad from an old Intel MacBook using an old XCode:
>>
>> Thanks for the suggestion. I'm pretty sure it is not a problem with
>> setting C*FLAGS,
>> since those show up as expected in sysroot. I think '-target' is
>> treated special
>> somehow and ignored, though I cannot find exactly why/where that is
>> happening.
>>
>> Even after my hack yesterday I found another problem though, and that
>> is the libraries
>> like 'openssl' that I was getting from 'mac ports' project
>> are of course built for the host CPU so won't link into the m1
>> compiled code.
>
> Yeah, you usually need to build the target (like cURL and c-ares) and
> all the dependencies (like IDN2, PCRE and OpenSSL) in this scenario.
>
> It has been my experience that cuRL is one of the tougher recipes you
> will encounter because it has so many dependendencies. It's not good
> or bad, it's just the way it is.
>
>> Do you know if there is an easy way to install ports for a non-native
>> CPU? I'm guessing not, and that
>> my best way forward is just to buy another m1 macos machine and build
>> directly on it.
>> But, if you know a way, please let me know.
>
> Native compilation will probably be easiest.
>
> If you want to cross-compile, then you will want (need?) a script like
> setenv-ios.sh to setup all your flags. Decide on a location, like
> /opt/ios/aarch64/. Then, for cURL, c-ares and each dependent library,
> you configure for the cross-compile (using --host and --build), and
> build each library for the common place (--prefix=/opt/ios/aarch64/).
> Your flags will need to include /opt/ios/aarch64/include in CPPFLAGS,
> and /opt/ios/aarch64/lib for LDFLAGS.
>
> The pain point of the cross-compile will be projects which do not
> honor your flags. The makefile authors will overwrite your CPPFLAGS,
> CFLAGS, CXXFLAGS and LDFLAGS, and it will break your cross-compile. I
> have patched a lot of makefiles over the years because of this
> problem.
>
> A good program to experiment with cross-compiles is OpenSSH. OpenSSH
> has two components - OpenSSH itself and OpenSSL as a dependency. (LDNS
> is optional and not required). Once you work out your methodology with
> OpenSSH, it will scale to bigger projects like cURL (modulo makefile
> authors stomping on your flags).
>
> Jeff

In the past I crosscompiled few things and used different approach. I
did not touch CFLAGS/CXXFLAGS/LDFLAGS as build scripts often used them
for their own purposes. Instead I set CC and CXX to point to my C/C++
crosscompilers and added any extra options there.

-- 
Regards,
Daniel
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Received on 2023-01-25