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Cross emerge gcc with which -march?
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gabord
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PostPosted: Mon Sep 17, 2018 6:10 am    Post subject: Cross emerge gcc with which -march? Reply with quote

Hi,

I would like to cross emerge gcc with the following command (and -march=armv8-a+crc set) on an amd64 build machine, but I get an error message.

Code:
aarch64-unknown-linux-gnu-emerge gcc


Code:
cc1plus: error: bad value (‘armv8-a+crc’) for ‘-march=’ switch
cc1plus: note: valid arguments to ‘-march=’ switch are: nocona core2 nehalem corei7 westmere sandybridge corei7-avx ivybridge core-avx-i haswell core-avx2 broadwell skylake skylake-avx512 cannonlake icelake-client icelake-server bonnell atom silvermont slm knl knm x86-64 eden-x2 nano nano-1000 nano-2000 nano-3000 nano-x2 eden-x4 nano-x4 k8 k8-sse3 opteron opteron-sse3 athlon64 athlon64-sse3 athlon-fx amdfam10 barcelona bdver1 bdver2 bdver3 bdver4 znver1 btver1 btver2 native


Every other package compiles correctly (around ~200), except this.
If I set -march to be the build architecture, gcc cross emerges, but none of the other packages do. I do not think this is a correct behavior for gcc, because -march means the target architecture, and not the build architecture, isn't it?
Which CFLAGS should I use?


The same thing happens with gcc-7.3.0-r3 and 8.2.0-r2.
My /usr/aarch64-unknown-linux-gnu/etc/portage/make.conf file:
Code:
ROOT=/usr/aarch64-unknown-linux-gnu/
ACCEPT_KEYWORDS="~arm64"
CFLAGS="-march=armv8-a+crc -O2 -pipe"
CXXFLAGS="${CFLAGS}"
PORTAGE_TMPDIR=${ROOT}var/tmp/


Full build log: https://pastebin.com/bbWiZF6y
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NeddySeagoon
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PostPosted: Mon Sep 17, 2018 7:35 am    Post subject: Reply with quote

gabord,

Welcome to Gentoo.

Do not set -march at all, just for gcc, while it is cross compiled.
The output gcc will run on any arm64 system and will itself obey the -march= when you run it on the target.

You can have portage set per package CFLAGS using both /etc/portage/env/ and /etc/portage/package.env/

-- edit --

That's the /usr/aarch64-unknown-linux-gnu/ ... files.
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gabord
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PostPosted: Mon Sep 17, 2018 7:50 am    Post subject: Reply with quote

NeddySeagoon wrote:
Welcome to Gentoo.

Thanks!

NeddySeagoon wrote:
Do not set -march at all, just for gcc, while it is cross compiled.

I will do that. What is the reason for this? Can I read about that in detail why gcc needs does this for cross compile? I tried to find information about the toolchain eclass, but could not find any.
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NeddySeagoon
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PostPosted: Mon Sep 17, 2018 7:54 am    Post subject: Reply with quote

gabord,

The simple answer is that its a feature of the gcc build system.
Leaving out -march is a workaround, not a fix.

If you want to save some build time, I have a an arm64 BINHOST that is publicly accessible.
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gabord
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PostPosted: Mon Sep 17, 2018 6:52 pm    Post subject: Reply with quote

NeddySeagoon wrote:
gabord,

The simple answer is that its a feature of the gcc build system.
Leaving out -march is a workaround, not a fix.

If you want to save some build time, I have a an arm64 BINHOST that is publicly accessible.


Thanks! And I will look into it in detail in the future why this is a feature, but it is not important now.
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