1The biggest problem when trying to compile U-Boot with clang is that 2almost all archs rely on storing gd in a global register and clang user 3manual states: "clang does not support global register variables; this 4is unlikely to be implemented soon because it requires additional LLVM 5backend support." 6 7Since version 3.4 the ARM backend can be instructed to leave r9 alone. 8Global registers themselves are not supported so some inline assembly is 9used to get its value. This does lead to larger code then strictly 10necessary, but at least works. 11 12NOTE: target compilation only work for _some_ ARM boards at the moment. 13Also AArch64 is not supported currently due to a lack of private libgcc 14support. Boards which reassign gd in c will also fail to compile, but there is 15in no strict reason to do so in the ARM world, since crt0.S takes care of this. 16These assignments can be avoided by changing the init calls but this is not in 17mainline yet. 18 19Debian (based) 20-------------- 21Binary packages can be installed as usual, e.g.: 22sudo apt-get install clang 23 24Note that we still use binutils for some tools so we must continue to set 25CROSS_COMPILE. To compile U-Boot with clang on linux without IAS use e.g.: 26make HOSTCC=clang rpi_2_defconfig 27make HOSTCC=clang CROSS_COMPILE=arm-linux-gnueabi- \ 28 CC="clang -target arm-linux-gnueabi" -j8 29 30It can also be used to compile sandbox: 31make HOSTCC=clang sandbox_defconfig 32make HOSTCC=clang CC=clang -j8 33 34FreeBSD 11 (Current): 35-------------------- 36Since llvm 3.4 is currently in the base system, the integrated as is 37incapable of building U-Boot. Therefore gas from devel/arm-gnueabi-binutils 38is used instead. It needs a symlinks to be picked up correctly though: 39 40ln -s /usr/local/bin/arm-gnueabi-freebsd-as /usr/bin/arm-freebsd-eabi-as 41 42# The following commands compile U-Boot using the clang xdev toolchain. 43# NOTE: CROSS_COMPILE and target differ on purpose! 44export CROSS_COMPILE=arm-gnueabi-freebsd- 45gmake rpi_2_defconfig 46gmake CC="clang -target arm-freebsd-eabi --sysroot /usr/arm-freebsd" -j8 47 48Given that U-Boot will default to gcc, above commands can be 49simplified with a simple wrapper script, listed below. 50 51/usr/local/bin/arm-gnueabi-freebsd-gcc 52--- 53#!/bin/sh 54 55exec clang -target arm-freebsd-eabi --sysroot /usr/arm-freebsd "$@" 56