Commit 5bfdcebf73f843b4a0968e87cff9ad6546358c8d
Committed by
Albert ARIBAUD
Albert ARIBAUD
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b477fe44ee
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README.clang: build command with clang
Cc: Albert ARIBAUD <albert.u.boot@aribaud.net> Signed-off-by: Jeroen Hofstee <jeroen@myspectrum.nl>
Showing 1 changed file with 56 additions and 0 deletions Side-by-side Diff
doc/README.clang
| 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 $TRIPLET -mllvm -arm-use-movt=0 -no-integrated-as" all V=1 -j8 | |
| 33 | + | |
| 34 | +FreeBSD 11 (Current): | |
| 35 | +-------------------- | |
| 36 | +Since llvm 3.4 is currently in the base system, the integrated as is | |
| 37 | +incapable of building U-Boot. Therefore gas from devel/arm-eabi-binutils | |
| 38 | +is used instead. It needs a symlinks to be picked up correctly though: | |
| 39 | + | |
| 40 | +ln -s /usr/local/bin/arm-eabi-as /usr/bin/arm-freebsd-eabi-as | |
| 41 | + | |
| 42 | +# The following commands compile U-Boot using the clang xdev toolchain. | |
| 43 | +# NOTE: CROSS_COMPILE and target differ on purpose! | |
| 44 | +export CROSS_COMPILE=arm-eabi- | |
| 45 | +gmake CC="clang -target arm-freebsd-eabi --sysroot /usr/arm-freebsd -no-integrated-as -mllvm -arm-use-movt=0" rpi_b_defconfig | |
| 46 | +gmake CC="clang -target arm-freebsd-eabi --sysroot /usr/arm-freebsd -no-integrated-as -mllvm -arm-use-movt=0" -j8 | |
| 47 | + | |
| 48 | +Given that u-boot will default to gcc, above commands can be | |
| 49 | +simplified with a simple wrapper script, listed below. | |
| 50 | + | |
| 51 | +/usr/local/bin/arm-eabi-gcc | |
| 52 | +--- | |
| 53 | +#!/bin/sh | |
| 54 | + | |
| 55 | +exec clang -target arm-freebsd-eabi --sysroot /usr/arm-freebsd -no-integrated-as -mllvm -arm-use-movt=0 "$@" |