| The biggest problem when trying to compile U-Boot with clang is that | |
| almost all archs rely on storing gd in a global register and clang user | |
| manual states: "clang does not support global register variables; this | |
| is unlikely to be implemented soon because it requires additional LLVM | |
| backend support." | |
| Since version 3.4 the ARM backend can be instructed to leave r9 alone. | |
| Global registers themselves are not supported so some inline assembly is | |
| used to get its value. This does lead to larger code then strictly | |
| necessary, but at least works. | |
| NOTE: target compilation only work for _some_ ARM boards at the moment. | |
| Also AArch64 is not supported currently due to a lack of private libgcc | |
| support. Boards which reassign gd in c will also fail to compile, but there is | |
| in no strict reason to do so in the ARM world, since crt0.S takes care of this. | |
| These assignments can be avoided by changing the init calls but this is not in | |
| mainline yet. | |
| Debian (based) | |
| -------------- | |
| Binary packages can be installed as usual, e.g.: | |
| sudo apt-get install clang | |
| Note that we still use binutils for some tools so we must continue to set | |
| CROSS_COMPILE. To compile U-Boot with clang on linux without IAS use e.g.: | |
| make HOSTCC=clang rpi_2_defconfig | |
| make HOSTCC=clang CROSS_COMPILE=arm-linux-gnueabi- \ | |
| CC="clang -target arm-linux-gnueabi" -j8 | |
| It can also be used to compile sandbox: | |
| make HOSTCC=clang sandbox_defconfig | |
| make HOSTCC=clang CC=clang -j8 | |
| FreeBSD 11 (Current): | |
| -------------------- | |
| Since llvm 3.4 is currently in the base system, the integrated as is | |
| incapable of building U-Boot. Therefore gas from devel/arm-gnueabi-binutils | |
| is used instead. It needs a symlinks to be picked up correctly though: | |
| ln -s /usr/local/bin/arm-gnueabi-freebsd-as /usr/bin/arm-freebsd-eabi-as | |
| # The following commands compile U-Boot using the clang xdev toolchain. | |
| # NOTE: CROSS_COMPILE and target differ on purpose! | |
| export CROSS_COMPILE=arm-gnueabi-freebsd- | |
| gmake rpi_2_defconfig | |
| gmake CC="clang -target arm-freebsd-eabi --sysroot /usr/arm-freebsd" -j8 | |
| Given that U-Boot will default to gcc, above commands can be | |
| simplified with a simple wrapper script, listed below. | |
| /usr/local/bin/arm-gnueabi-freebsd-gcc | |
| --- | |
| #!/bin/sh | |
| exec clang -target arm-freebsd-eabi --sysroot /usr/arm-freebsd "$@" |