| Jeroen Hofstee | 5bfdceb | 2014-09-10 20:08:52 +0200 | [diff] [blame] | 1 | The biggest problem when trying to compile U-boot with clang is that |
| 2 | almost all archs rely on storing gd in a global register and clang user |
| 3 | manual states: "clang does not support global register variables; this |
| 4 | is unlikely to be implemented soon because it requires additional LLVM |
| 5 | backend support." |
| 6 | |
| 7 | Since version 3.4 the ARM backend can be instructed to leave r9 alone. |
| 8 | Global registers themselves are not supported so some inline assembly is |
| 9 | used to get its value. This does lead to larger code then strictly |
| 10 | necessary, but at least works. |
| 11 | |
| 12 | NOTE: target compilation only work for _some_ ARM boards at the moment. |
| 13 | Also Aarch64 is not supported: Most notably boards which aren't using |
| 14 | the generic board will fail to compile, but since those are expected |
| 15 | to be converted this will solve itself. Boards which reassign gd in c |
| 16 | will also fail to compile, but there is in no strict reason to do so |
| 17 | in the ARM world, since crt0.S takes care of this. These assignments |
| 18 | can be avoided by changing the init calls but this is not in mainline yet. |
| 19 | |
| 20 | NOTE: without the -mllvm -arm-use-movt=0 flags u-boot will compile |
| 21 | fine, but llvm might hardcode addresses in movw / movt pairs, which |
| 22 | cannot be relocated and u-boot will fail at runtime. |
| 23 | |
| 24 | Debian (based) |
| 25 | -------------- |
| 26 | Binary packages can be installed as usual, e.g.: |
| 27 | sudo apt-get install clang |
| 28 | |
| 29 | To compile U-Boot with clang on linux without IAS use e.g.: |
| 30 | export TRIPLET=arm-linux-gnueabi && export CROSS_COMPILE="$TRIPLET-" |
| 31 | make HOSTCC=clang CC="clang -target $TRIPLET -mllvm -arm-use-movt=0 -no-integrated-as" rpi_b_defconfig |
| 32 | make HOSTCC=clang CC="clang -target $TRIPLET -mllvm -arm-use-movt=0 -no-integrated-as" all V=1 -j8 |
| 33 | |
| 34 | FreeBSD 11 (Current): |
| 35 | -------------------- |
| 36 | Since llvm 3.4 is currently in the base system, the integrated as is |
| 37 | incapable of building U-Boot. Therefore gas from devel/arm-eabi-binutils |
| 38 | is used instead. It needs a symlinks to be picked up correctly though: |
| 39 | |
| 40 | ln -s /usr/local/bin/arm-eabi-as /usr/bin/arm-freebsd-eabi-as |
| 41 | |
| 42 | # The following commands compile U-Boot using the clang xdev toolchain. |
| 43 | # NOTE: CROSS_COMPILE and target differ on purpose! |
| 44 | export CROSS_COMPILE=arm-eabi- |
| 45 | gmake CC="clang -target arm-freebsd-eabi --sysroot /usr/arm-freebsd -no-integrated-as -mllvm -arm-use-movt=0" rpi_b_defconfig |
| 46 | gmake CC="clang -target arm-freebsd-eabi --sysroot /usr/arm-freebsd -no-integrated-as -mllvm -arm-use-movt=0" -j8 |
| 47 | |
| 48 | Given that u-boot will default to gcc, above commands can be |
| 49 | simplified with a simple wrapper script, listed below. |
| 50 | |
| 51 | /usr/local/bin/arm-eabi-gcc |
| 52 | --- |
| 53 | #!/bin/sh |
| 54 | |
| 55 | exec clang -target arm-freebsd-eabi --sysroot /usr/arm-freebsd -no-integrated-as -mllvm -arm-use-movt=0 "$@" |
| 56 | |