linux/arch
Joel Stanley 72e7bcc2cd powerpc/32: Avoid unsupported flags with clang
When building for ppc32 with clang these flags are unsupported:

  -ffixed-r2 and -mmultiple

llvm's lib/Target/PowerPC/PPCRegisterInfo.cpp marks r2 as reserved on
when building for SVR4ABI and !ppc64:

  // The SVR4 ABI reserves r2 and r13
  if (Subtarget.isSVR4ABI()) {
    // We only reserve r2 if we need to use the TOC pointer. If we have no
    // explicit uses of the TOC pointer (meaning we're a leaf function with
    // no constant-pool loads, etc.) and we have no potential uses inside an
    // inline asm block, then we can treat r2 has an ordinary callee-saved
    // register.
    const PPCFunctionInfo *FuncInfo = MF.getInfo<PPCFunctionInfo>();
    if (!TM.isPPC64() || FuncInfo->usesTOCBasePtr() || MF.hasInlineAsm())
      markSuperRegs(Reserved, PPC::R2);  // System-reserved register
    markSuperRegs(Reserved, PPC::R13); // Small Data Area pointer register
  }

This means we can safely omit -ffixed-r2 when building for 32-bit
targets.

The -mmultiple/-mno-multiple flags are not supported by clang, so
platforms that might support multiple miss out on using multiple word
instructions.

We wrap these flags in cc-option so that when Clang gains support the
kernel will be able use these flags.

Clang 8 can then build a ppc44x_defconfig which boots in Qemu:

  make CC=clang-8 ARCH=powerpc CROSS_COMPILE=powerpc-linux-gnu-  ppc44x_defconfig
  ./scripts/config -e CONFIG_DEVTMPFS -d DEVTMPFS_MOUNT
  make CC=clang-8 ARCH=powerpc CROSS_COMPILE=powerpc-linux-gnu-

  qemu-system-ppc -M bamboo \
   -kernel arch/powerpc/boot/zImage \
   -dtb arch/powerpc/boot/dts/bamboo.dtb \
   -initrd ~/ppc32-440-rootfs.cpio \
   -nographic -serial stdio -monitor pty -append "console=ttyS0"

Link: https://github.com/ClangBuiltLinux/linux/issues/261
Link: https://bugs.llvm.org/show_bug.cgi?id=39556
Link: https://bugs.llvm.org/show_bug.cgi?id=39555
Signed-off-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
2018-12-20 20:53:11 +11:00
..
alpha TTY/Serial fixes for 4.20-rc2 2018-11-10 13:32:14 -06:00
arc mm: remove include/linux/bootmem.h 2018-10-31 08:54:16 -07:00
arm s390 updates for 4.20-rc2 2018-11-09 06:30:44 -06:00
arm64 arm64 fixes: 2018-11-10 07:07:21 -06:00
c6x c6x changes for 4.20 2018-10-31 15:39:25 -07:00
csky csky: dtb Kbuild fixup patches for linux-4.20-rc1 2018-11-01 09:04:30 -07:00
h8300 mm: remove include/linux/bootmem.h 2018-10-31 08:54:16 -07:00
hexagon mm: remove include/linux/bootmem.h 2018-10-31 08:54:16 -07:00
ia64 memblock: stop using implicit alignment to SMP_CACHE_BYTES 2018-10-31 08:54:16 -07:00
m68k s390 updates for 4.20-rc2 2018-11-09 06:30:44 -06:00
microblaze s390 updates for 4.20-rc2 2018-11-09 06:30:44 -06:00
mips MIPS: Fix `dma_alloc_coherent' returning a non-coherent allocation 2018-11-05 10:08:13 -08:00
nds32 s390 updates for 4.20-rc2 2018-11-09 06:30:44 -06:00
nios2 mm: remove include/linux/bootmem.h 2018-10-31 08:54:16 -07:00
openrisc mm: remove include/linux/bootmem.h 2018-10-31 08:54:16 -07:00
parisc s390 updates for 4.20-rc2 2018-11-09 06:30:44 -06:00
powerpc powerpc/32: Avoid unsupported flags with clang 2018-12-20 20:53:11 +11:00
riscv RISC-V: refresh defconfig 2018-11-01 17:04:07 -07:00
s390 s390 updates for 4.20-rc2 2018-11-09 06:30:44 -06:00
sh mm: remove include/linux/bootmem.h 2018-10-31 08:54:16 -07:00
sparc Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/sparc 2018-11-01 09:07:04 -07:00
um for-linus-20181109 2018-11-09 16:31:51 -06:00
unicore32 memblock: stop using implicit alignment to SMP_CACHE_BYTES 2018-10-31 08:54:16 -07:00
x86 Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-11-11 16:41:50 -06:00
xtensa Xtensa fixes and cleanups for v4.20: 2018-11-01 14:32:43 -07:00
.gitignore
Kconfig New gcc plugin: stackleak 2018-11-01 11:46:27 -07:00