crossdev with GCC+LLVM toolchains

[viacheslavg]

Hello,

Please, help me to understand following:

I have aarch64-unknown-linux-gnu crossdev env configured in according to https://wiki.gentoo.org/wiki/Crossdev. It uses GCC toolchain. Everything works fine here.

Additionally I have LLVM/clang on my system with LLVM_TARGETS="AArch64". So, my clang is capable of crosscompiling for aarch64. right?

As per documentation it is clear that I can't fully setup LLVM crossdev for "-gnu" with

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crossdev --llvm -t aarch64-unknown-linux-gnu

because glibc can't be compiled with clang.

Is it possible *on top* of my existing aarch64-unknown-linux-gnu env add support of clang cross compiling?

For example, if I try to crosscompile firefox with USE="clang" I have

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 0:00.95 checking for the target C compiler... not found
 0:00.95 DEBUG: _cc: Looking for aarch64-unknown-linux-gnu-clang-21
 0:00.95 ERROR: Cannot find the target C compiler

which is expected.

If I try to manually install clang-crossdev-wrappers (manually unmasking it), it provides respective symlinks but now I have

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 0:00.96 DEBUG: Executing: `/usr/lib/llvm/21/bin/aarch64-unknown-linux-gnu-clang-21 --sysroot /usr/aarch64-unknown-linux-gnu /var/tmp/portage/www-client/firefox-147.0.1/temp/conftest_rog1cao.c -E`
 0:00.96 DEBUG: The command returned non-zero exit status 1.
 0:00.96 DEBUG: Its error output was:
 0:00.96 DEBUG: | clang-21: error: configuration file '/etc/clang/cross/aarch64-unknown-linux-gnu.cfg' cannot be opened: No such file or directory
 0:00.96 ERROR: Command `/usr/lib/llvm/21/bin/aarch64-unknown-linux-gnu-clang-21 --sysroot /usr/aarch64-unknown-linux-gnu /var/tmp/portage/www-client/firefox-147.0.1/temp/conftest_rog1cao.c -E` failed with exit status 1.

i.e. I need some extra clang configuration for cross env.

Am I doing something nasty here? Is it possible to make clang crosscompile for aarch64 with glibc somewhow?

Thanks

[turtles]

Sort answer yes its Gentoo anything is possible. 3 observations;

• Seems like you still need the target's headers and libraries, to get a functional glibc environment for AArch64 via crossdev I'd try:

  Code: Select all

  crossdev -s4 --target aarch64-unknown-linux-gnu

  The -s4 (Also build a full compiler) command I'd think builds a target environment using GCC.
• Invoking Clang: Since Clang is a native cross-compiler (assuming LLVM_TARGETS="AArch64" is set in make.conf), you just need to point it to that new sysroot so it finds the right glibc:
  I'd make a test file (hello.c) and test it

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  #include <stdio.h>
  
  int main() {
  printf("Hello from AArch64!\n");
  return 0;
  }
  

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  clang --target=aarch64-unknown-linux-gnu --sysroot=/usr/aarch64-unknown-linux-gnu hello.c

• To use aarch64-unknown-linux-gnu-emerge with Clang, I'd try some kind of a config at /usr/aarch64-unknown-linux-gnu/etc/portage/make.conf:

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  CC="clang --target=aarch64-unknown-linux-gnu"
  CXX="clang++ --target=aarch64-unknown-linux-gnu"

  If you already have one you might share it so others can look it over

Hope that helps, I am not a expert on crossdev but I use it.

[viacheslavg]

turtles, thanks for support.

Right, I have

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crossdev -s4 --target aarch64-unknown-linux-gnu

setup correctly. cross-compilation with gcc works fine.

This

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clang --target=aarch64-unknown-linux-gnu --sysroot=/usr/aarch64-unknown-linux-gnu hello.c

also works as expected. I have aarch64 binary output.

However firefox is not able to cross-compile. Errors are mentioned in the first post.

I also tried to put

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CC="clang --target=aarch64-unknown-linux-gnu"
CXX="clang++ --target=aarch64-unknown-linux-gnu"

in make.conf.
Still fails with:

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 0:05.39 checking for the target C compiler... not found
 0:05.39 DEBUG: _cc: Looking for aarch64-unknown-linux-gnu-clang-21
 0:05.39 ERROR: Cannot find the target C compiler

Does firefox supports cross-compilation at all? Maybe it is not supported? I can't find any info.

My make.conf looks like this

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# Note: profile variables are set/overridden in profile/ files:
# etc/portage/profile/use.force (overrides kernel_* USE variables)
# etc/portage/profile/make.defaults (overrides ARCH, KERNEL, ELIBC variables)

#CHOST=aarch64-unknown-linux-gnu
CBUILD=x86_64-pc-linux-gnu

ROOT=/usr/aarch64-unknown-linux-gnu/
PKGDIR=/usr/aarch64-unknown-linux-gnu/var/cache/binpkgs/
PORTAGE_TMPDIR=/var/tmp/

ACCEPT_KEYWORDS="~arm64"

COMMON_FLAGS="-O2 -pipe -fomit-frame-pointer -march=armv8-a+crc -mtune=cortex-a53"
CFLAGS="${COMMON_FLAGS}"
CXXFLAGS="${COMMON_FLAGS}"
FCFLAGS="${COMMON_FLAGS}"
FFLAGS="${COMMON_FLAGS}"
CXXFLAGS="${CFLAGS}"

#CC="clang --target=aarch64-unknown-linux-gnu"
#CXX="clang++ --target=aarch64-unknown-linux-gnu"

MAKEOPTS="-j12"
EMERGE_DEFAULT_OPTS="--jobs=1 --load-average=4 --autounmask-write"

CPU_FLAGS_ARM="edsp neon thumb vfp vfpv3 vfpv4 vfp-d32 aes sha1 sha2 crc32 v4 v5 v6 v7 v8 thumb2"

VIDEO_CARDS="lima"

FEATURES="-collision-protect -pid-sandbox -network-sandbox sandbox"

FEATURES="${FEATURES} buildpkg"
BINPKG_FORMAT="gpkg"

FEATURES="${FEATURES} getbinpkg"
PORTAGE_BINHOST=""
PORTAGE_BINHOST="${PORTAGE_BINHOST} http://192.168.1.171/aarch64-packages"

USE="${ARCH} wayland gles2 gles2-only -opengl -vulkan -gnome -kde -jumbo-build -introspection -vala"

LLVM_TARGETS="AArch64"

ACCEPT_LICENSE="curl"

GENTOO_MIRRORS="http://gentoo.osuosl.org/ http://trumpetti.atm.tut.fi/gentoo/ http://distfiles.gentoo.org"