baremetal clang toolchain does not define _GNU_SOURCE [254916723]

Fixed

Bug

Status Update

No update yet.

Description

to...@google.com

created issue #1

Oct 21, 2022 10:09PM

When building [libcxx], I noticed that _GNU_SOURCE is not defined automatically by armv7m-cros-eabi-clang++.

Some comparisons (where empty.cc is an empty file):

_GNU_SOURCE is defined:

clang++ -E -dD -o empty empty.cc
armv7a-cros-linux-gnueabihf-clang++ -E -dD -o empty empty.cc

_GNU_SOURCE is not defined:

armv7m-cros-eabi-clang++ -E -dD -o empty empty.cc
/opt/coreboot-sdk/bin/arm-eabi-g++ -E -dD -o empty empty.cc
arm-none-eabi-clang++ -E -dD -o empty empty.cc

It looks the baremetal variants don't define it. I guess the assumption is that baremetal targets won't use libc?

Comments

bl...@google.com <bl...@google.com> #2Oct 21, 2022 10:23PM

Assigned to in...@google.com.

Automated by Blunderbuss job chromeos-toolchain-blunderbuss for component 1038090.

in...@google.com <in...@google.com> #3Oct 21, 2022 10:39PM

*Should* _GNU_SOURCE be defined? My understanding is that it is a macro you should define yourself in your source code if you want certain features from GNU libc.

to...@google.com <to...@google.com> #4Oct 21, 2022 11:15PM

I agree, that is the question. Looks like it was discussed in this thread.

The reason I brought this up is that I've hit this a few times when trying to build:

The failures aren't immediately obvious, since they're usually related to the other defines that _GNU_SOURCE enables. I'd be fine if we were consistent across versions of clang, but the inconsistency makes it annoying.

ma...@google.com <ma...@google.com> #5Oct 22, 2022 02:33AM

I am guessing that `_GNU_SOURCE` when building libc++ is not enough for baremetal c++ projects.
The project sources will still run into issues if they do not define `_GNU_SOURCE` since most features are part of headers.

I can send a patch to upstream and ask for review.

to...@google.com <to...@google.com> #6Oct 28, 2022 06:40PM

Upstream review: https://reviews.llvm.org/D136712

ap...@google.com <ap...@google.com> #7Nov 2, 2022 04:54PM

Project: chromiumos/platform/ec
Branch: main

commit e89aa6426ee7b4a969dd12c7ed32214cc5b28028
Author: Tom Hughes <tomhughes@chromium.org>
Date: Tue Nov 01 14:09:00 2022

Makefile.toolchain: Define _GNU_SOURCE when using clang

g++ defines _GNU_SOURCE, but the baremetal clang++ toolchain we're using
does not. When using libcxx + newlib, _GNU_SOURCE needs to be defined
for compilation to succeed.

BRANCH=none
BUG=b:254916723
TEST=./util/compare_build.sh -b all -j 120
=> MATCH

Signed-off-by: Tom Hughes <tomhughes@chromium.org>
Change-Id: Ieda973980157ecc37c2aa1afcb35cbf62bfa3c51
Reviewed-on:

https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3995333
Reviewed-by: Peter Marheine <pmarheine@chromium.org>

M Makefile.toolchain

https://chromium-review.googlesource.com/3995333

ap...@google.com <ap...@google.com> #8Nov 19, 2022 06:07PM

Project: chromiumos/overlays/chromiumos-overlay
Branch: main

commit cee5e48fcf61bd92e4be4cf4712a939ec0462d29
Author: Manoj Gupta <manojgupta@google.com>
Date: Fri Nov 18 13:36:00 2022

llvm: get patches from upstream

reviews.llvm.org/rG2497d5aa7716a664c4f73df1980b026c906c7522

2497d5aa7716 Define _GNU_SOURCE for arm baremetal in C++ mode.

BUG=b:234507656, b:254916723
TEST=CQ

Change-Id: I39f9631c65af49542eb65dfd1b18e122ff16c761
Reviewed-on:

https://chromium-review.googlesource.com/c/chromiumos/overlays/chromiumos-overlay/+/4038332
Commit-Queue: Manoj Gupta <manojgupta@chromium.org>
Reviewed-by: Tom Hughes <tomhughes@chromium.org>
Tested-by: Manoj Gupta <manojgupta@chromium.org>
Reviewed-by: George Burgess <gbiv@chromium.org>

M sys-devel/llvm/files/PATCHES.json
A sys-devel/llvm/files/cherry/2497d5aa7716a664c4f73df1980b026c906c7522.patch
M sys-devel/llvm/llvm-15.0_pre465103_p20220825-r7.ebuild

https://chromium-review.googlesource.com/4038332

ma...@google.com <ma...@google.com> Nov 19, 2022 06:08PM

Marked as fixed.

ap...@google.com <ap...@google.com> #9Dec 2, 2022 09:59PM

Project: chromiumos/platform/ec
Branch: main

commit 9f6d6ca10611cd1af3d81534baa674db335a4dc0
Author: Manoj Gupta <manojgupta@google.com>
Date: Fri Dec 02 20:33:14 2022

Remove some C++ toolchain workarounds

Remove toolchain workarounds for C++ header files
location and GNU_SOURCE as they are fixed in clang.

BRANCH=none
BUG=b:254916723, b:234507656, b:241489000
TEST=./util/compare_build.sh -b all -j 120

Change-Id: I8e1cd634c1085803fddcc2dec8f5667453a5e0e6
Signed-off-by: Manoj Gupta <manojgupta@google.com>
Reviewed-on:

https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/4074063
Code-Coverage: Zoss <zoss-cl-coverage@prod.google.com>
Tested-by: Manoj Gupta <manojgupta@chromium.org>
Commit-Queue: Manoj Gupta <manojgupta@chromium.org>
Reviewed-by: Tom Hughes <tomhughes@chromium.org>

M Makefile.toolchain
M cmake/toolchain-armv7m.cmake

https://chromium-review.googlesource.com/4074063