On Mon, Jul 12, 2021 at 11:10:04AM +0000, Tor Vic wrote: > On some distros and configurations, it might be useful to allow for > specifying a directory where Clang stores its ThinLTO cache. > > More specifically, when building the VirtualBox extramodules on Arch with > its proper 'makepkg' build system and DKMS, against an already installed > ThinLTO kernel, the build fails because it tries to create the ThinLTO > cache in a directory that is not user-writable. > > A similar problem has been reported with openSUSE's OBS build system. > > Add a Kconfig option that allows users to choose a directory in which > Clang's ThinLTO can store its cache. Ah-ha, good idea. Thanks! Question below... > > Link: https://github.com/ClangBuiltLinux/linux/issues/1104 > Signed-off-by: Tor Vic <torvic9@xxxxxxxxxxx> > --- > Makefile | 5 +++-- > arch/Kconfig | 10 ++++++++++ > scripts/Makefile.lib | 4 ++++ > scripts/Makefile.modfinal | 4 ++++ > 4 files changed, 21 insertions(+), 2 deletions(-) > > diff --git a/Makefile b/Makefile > index c3f9bd191b89..472bc8bfff03 100644 > --- a/Makefile > +++ b/Makefile > @@ -932,7 +932,8 @@ endif > ifdef CONFIG_LTO_CLANG > ifdef CONFIG_LTO_CLANG_THIN > CC_FLAGS_LTO := -flto=thin -fsplit-lto-unit > -KBUILD_LDFLAGS += --thinlto-cache-dir=$(extmod_prefix).thinlto-cache > +export thinlto-dir = $(if > $(CONFIG_LTO_CLANG_THIN_CACHEDIR),$(CONFIG_LTO_CLANG_THIN_CACHEDIR)/) > +KBUILD_LDFLAGS += > --thinlto-cache-dir=$(thinlto-dir)$(extmod_prefix).thinlto-cache > else > CC_FLAGS_LTO := -flto > endif > @@ -1728,7 +1729,7 @@ PHONY += compile_commands.json > > clean-dirs := $(KBUILD_EXTMOD) > clean: rm-files := $(KBUILD_EXTMOD)/Module.symvers > $(KBUILD_EXTMOD)/modules.nsdeps \ > - $(KBUILD_EXTMOD)/compile_commands.json $(KBUILD_EXTMOD)/.thinlto-cache > + $(KBUILD_EXTMOD)/compile_commands.json > $(thinlto-dir)$(KBUILD_EXTMOD)/.thinlto-cache > > PHONY += help > help: > diff --git a/arch/Kconfig b/arch/Kconfig > index 129df498a8e1..19e4d140e12a 100644 > --- a/arch/Kconfig > +++ b/arch/Kconfig > @@ -696,6 +696,16 @@ config LTO_CLANG_THIN > https://clang.llvm.org/docs/ThinLTO.html > > If unsure, say Y. > + > +config LTO_CLANG_THIN_CACHEDIR > + string "Clang ThinLTO cache directory" > + depends on LTO_CLANG_THIN > + default "" > + help > + This option allows users to choose a directory that stores > + Clang's ThinLTO cache. > + Leave empty for default. > + > endchoice > > config ARCH_SUPPORTS_CFI_CLANG > diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib > index 10950559b223..bca87a6aa35b 100644 > --- a/scripts/Makefile.lib > +++ b/scripts/Makefile.lib > @@ -197,6 +197,10 @@ endif > part-of-module = $(if $(filter $(basename $@).o, $(real-obj-m)),y) > quiet_modtag = $(if $(part-of-module),[M], ) > > +ifdef CONFIG_LTO_CLANG_THIN > +KBUILD_LDFLAGS += > --thinlto-cache-dir=$(thinlto-dir)$(extmod-prefix).thinlto-cache > +endif > + > modkern_cflags = \ > $(if $(part-of-module), \ > $(KBUILD_CFLAGS_MODULE) $(CFLAGS_MODULE), \ > diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal > index 5e9b8057fb24..ab0d72e21318 100644 > --- a/scripts/Makefile.modfinal > +++ b/scripts/Makefile.modfinal > @@ -35,6 +35,10 @@ ifdef CONFIG_LTO_CLANG > # avoid a second slow LTO link > prelink-ext := .lto > > +ifdef CONFIG_LTO_CLANG_THIN > +KBUILD_LDFLAGS += > --thinlto-cache-dir=$(thinlto-dir)$(extmod-prefix).thinlto-cache > +endif # CONFIG_LTO_CLANG_THIN > + > # ELF processing was skipped earlier because we didn't have native code, > # so let's now process the prelinked binary before we link the module. Why are these changes needed in Makefile.lib and Makefile.modfinal? Isn't KBUILD_LDFLAGS already populated from the top-level Makefile? -- Kees Cook
