72e7bcc2cd
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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.