1*4882a593SmuzhiyunThe biggest problem when trying to compile U-Boot with clang is that 2*4882a593Smuzhiyunalmost all archs rely on storing gd in a global register and clang user 3*4882a593Smuzhiyunmanual states: "clang does not support global register variables; this 4*4882a593Smuzhiyunis unlikely to be implemented soon because it requires additional LLVM 5*4882a593Smuzhiyunbackend support." 6*4882a593Smuzhiyun 7*4882a593SmuzhiyunSince version 3.4 the ARM backend can be instructed to leave r9 alone. 8*4882a593SmuzhiyunGlobal registers themselves are not supported so some inline assembly is 9*4882a593Smuzhiyunused to get its value. This does lead to larger code then strictly 10*4882a593Smuzhiyunnecessary, but at least works. 11*4882a593Smuzhiyun 12*4882a593SmuzhiyunNOTE: target compilation only work for _some_ ARM boards at the moment. 13*4882a593SmuzhiyunAlso Aarch64 is not supported: Most notably boards which aren't using 14*4882a593Smuzhiyunthe generic board will fail to compile, but since those are expected 15*4882a593Smuzhiyunto be converted this will solve itself. Boards which reassign gd in c 16*4882a593Smuzhiyunwill also fail to compile, but there is in no strict reason to do so 17*4882a593Smuzhiyunin the ARM world, since crt0.S takes care of this. These assignments 18*4882a593Smuzhiyuncan be avoided by changing the init calls but this is not in mainline yet. 19*4882a593Smuzhiyun 20*4882a593SmuzhiyunNOTE: without the -mllvm -arm-use-movt=0 flags U-Boot will compile 21*4882a593Smuzhiyunfine, but llvm might hardcode addresses in movw / movt pairs, which 22*4882a593Smuzhiyuncannot be relocated and U-Boot will fail at runtime. 23*4882a593Smuzhiyun 24*4882a593SmuzhiyunDebian (based) 25*4882a593Smuzhiyun-------------- 26*4882a593SmuzhiyunBinary packages can be installed as usual, e.g.: 27*4882a593Smuzhiyunsudo apt-get install clang 28*4882a593Smuzhiyun 29*4882a593SmuzhiyunNote that we still use binutils for some tools so we must continue to set 30*4882a593SmuzhiyunCROSS_COMPILE. To compile U-Boot with clang on linux without IAS use e.g.: 31*4882a593Smuzhiyunmake HOSTCC=clang rpi_2_defconfig 32*4882a593Smuzhiyunmake HOSTCC=clang CROSS_COMPILE=arm-linux-gnueabi- CC=clang -j8 33*4882a593Smuzhiyun 34*4882a593SmuzhiyunIt can also be used to compile sandbox: 35*4882a593Smuzhiyunmake HOSTCC=clang sandbox_defconfig 36*4882a593Smuzhiyunmake HOSTCC=clang CC=clang -j8 37*4882a593Smuzhiyun 38*4882a593SmuzhiyunFreeBSD 11 (Current): 39*4882a593Smuzhiyun-------------------- 40*4882a593SmuzhiyunSince llvm 3.4 is currently in the base system, the integrated as is 41*4882a593Smuzhiyunincapable of building U-Boot. Therefore gas from devel/arm-gnueabi-binutils 42*4882a593Smuzhiyunis used instead. It needs a symlinks to be picked up correctly though: 43*4882a593Smuzhiyun 44*4882a593Smuzhiyunln -s /usr/local/bin/arm-gnueabi-freebsd-as /usr/bin/arm-freebsd-eabi-as 45*4882a593Smuzhiyun 46*4882a593Smuzhiyun# The following commands compile U-Boot using the clang xdev toolchain. 47*4882a593Smuzhiyun# NOTE: CROSS_COMPILE and target differ on purpose! 48*4882a593Smuzhiyunexport CROSS_COMPILE=arm-gnueabi-freebsd- 49*4882a593Smuzhiyungmake rpi_2_defconfig 50*4882a593Smuzhiyungmake CC="clang -target arm-freebsd-eabi --sysroot /usr/arm-freebsd" -j8 51*4882a593Smuzhiyun 52*4882a593SmuzhiyunGiven that U-Boot will default to gcc, above commands can be 53*4882a593Smuzhiyunsimplified with a simple wrapper script, listed below. 54*4882a593Smuzhiyun 55*4882a593Smuzhiyun/usr/local/bin/arm-gnueabi-freebsd-gcc 56*4882a593Smuzhiyun--- 57*4882a593Smuzhiyun#!/bin/sh 58*4882a593Smuzhiyun 59*4882a593Smuzhiyunexec clang -target arm-freebsd-eabi --sysroot /usr/arm-freebsd "$@" 60