On Wed, Apr 14, 2021 at 11:48 AM <ojeda@xxxxxxxxxx> wrote: > > From: Miguel Ojeda <ojeda@xxxxxxxxxx> > > To support Rust under GCC-built kernels, we need to save the flags that > would have been passed if the kernel was being compiled with Clang. > > The reason is that bindgen -- the tool we use to generate Rust bindings > to the C side of the kernel -- relies on libclang to parse C. Ideally: > > - bindgen would support a GCC backend (requested at [1]), > > - or the Clang driver would be perfectly compatible with GCC, > including plugins. Unlikely, of course, but perhaps a big > subset of configs may be possible to guarantee to be kept > compatible nevertheless. > > This is also the reason why GCC builds are very experimental and some > configurations may not work (e.g. GCC_PLUGIN_RANDSTRUCT). However, > we keep GCC builds working (for some example configs) in the CI > to avoid diverging/regressing further, so that we are better prepared > for the future when a solution might become available. > > [1] https://github.com/rust-lang/rust-bindgen/issues/1949 > > Link: https://github.com/Rust-for-Linux/linux/issues/167 > > Co-developed-by: Alex Gaynor <alex.gaynor@xxxxxxxxx> > Signed-off-by: Alex Gaynor <alex.gaynor@xxxxxxxxx> > Co-developed-by: Geoffrey Thomas <geofft@xxxxxxxxxxxxx> > Signed-off-by: Geoffrey Thomas <geofft@xxxxxxxxxxxxx> > Co-developed-by: Finn Behrens <me@xxxxxxxxx> > Signed-off-by: Finn Behrens <me@xxxxxxxxx> > Co-developed-by: Adam Bratschi-Kaye <ark.email@xxxxxxxxx> > Signed-off-by: Adam Bratschi-Kaye <ark.email@xxxxxxxxx> > Co-developed-by: Wedson Almeida Filho <wedsonaf@xxxxxxxxxx> > Signed-off-by: Wedson Almeida Filho <wedsonaf@xxxxxxxxxx> > Signed-off-by: Miguel Ojeda <ojeda@xxxxxxxxxx> > --- > Makefile | 27 ++++++++++++++++----------- > 1 file changed, 16 insertions(+), 11 deletions(-) > > diff --git a/Makefile b/Makefile > index d4784d181123..9c75354324ed 100644 > --- a/Makefile > +++ b/Makefile > @@ -559,26 +559,31 @@ ifdef building_out_of_srctree > { echo "# this is build directory, ignore it"; echo "*"; } > .gitignore > endif > > -# The expansion should be delayed until arch/$(SRCARCH)/Makefile is included. > -# Some architectures define CROSS_COMPILE in arch/$(SRCARCH)/Makefile. > -# CC_VERSION_TEXT is referenced from Kconfig (so it needs export), > -# and from include/config/auto.conf.cmd to detect the compiler upgrade. > -CC_VERSION_TEXT = $(shell $(CC) --version 2>/dev/null | head -n 1 | sed 's/\#//g') > +TENTATIVE_CLANG_FLAGS := -Werror=unknown-warning-option > > -ifneq ($(findstring clang,$(CC_VERSION_TEXT)),) > ifneq ($(CROSS_COMPILE),) > -CLANG_FLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%)) > +TENTATIVE_CLANG_FLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%)) > GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)elfedit)) > -CLANG_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE)) > +TENTATIVE_CLANG_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE)) > GCC_TOOLCHAIN := $(realpath $(GCC_TOOLCHAIN_DIR)/..) > endif > ifneq ($(GCC_TOOLCHAIN),) > -CLANG_FLAGS += --gcc-toolchain=$(GCC_TOOLCHAIN) > +TENTATIVE_CLANG_FLAGS += --gcc-toolchain=$(GCC_TOOLCHAIN) > endif > ifneq ($(LLVM_IAS),1) > -CLANG_FLAGS += -no-integrated-as > +TENTATIVE_CLANG_FLAGS += -no-integrated-as > endif > -CLANG_FLAGS += -Werror=unknown-warning-option > + > +export TENTATIVE_CLANG_FLAGS I'm ok with this approach, but I'm curious: If the user made a copy of the CLANG_FLAGS variable and modified its copy, would TENTATIVE_CLANG_FLAGS even be necessary? IIUC, TENTATIVE_CLANG_FLAGS is used to filter out certain flags before passing them to bindgen? Or, I'm curious whether you even need to rename this variable (or create a new variable) at all? Might make for a shorter diff if you just keep the existing identifier (CLANG_FLAGS), but create them unconditionally (at least not conditional on CC=clang). > + > +# The expansion should be delayed until arch/$(SRCARCH)/Makefile is included. > +# Some architectures define CROSS_COMPILE in arch/$(SRCARCH)/Makefile. > +# CC_VERSION_TEXT is referenced from Kconfig (so it needs export), > +# and from include/config/auto.conf.cmd to detect the compiler upgrade. > +CC_VERSION_TEXT = $(shell $(CC) --version 2>/dev/null | head -n 1 | sed 's/\#//g') > + > +ifneq ($(findstring clang,$(CC_VERSION_TEXT)),) > +CLANG_FLAGS += $(TENTATIVE_CLANG_FLAGS) > KBUILD_CFLAGS += $(CLANG_FLAGS) > KBUILD_AFLAGS += $(CLANG_FLAGS) > export CLANG_FLAGS > -- > 2.17.1 > -- Thanks, ~Nick Desaulniers
