> Masahiro Yamada <masahiroy@xxxxxxxxxx> hat am 13.07.2021 12:45 geschrieben: > > > On Mon, Jul 12, 2021 at 8:10 PM Tor Vic <torvic9@xxxxxxxxxxx> 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. > > > > Link: https://github.com/ClangBuiltLinux/linux/issues/1104 > > Signed-off-by: Tor Vic <torvic9@xxxxxxxxxxx> > > > I do not understand. > > Currently, .thinlto-cache is created in the same directory > as the other objects. (right under $(KBUILD_EXTMOD)) > > If you build in a read-only directory, you cannot put > any build artifact (not limited to the thinlto cache) there. > > Why did changing the location of .thinlto-cache > solve your problem? > Sorry, I accidentally sent the message before completing it... So, when building an out-of-tree module on Arch using DKMS, I get the following error message: Error: Permission denied LLVM ERROR: ThinLTO: Can't get a temporary file The reason for this seems to be that DKMS looks for the cache inside the installed kernel's modules/headers folder, which on Arch is in /usr/lib/modules/$kernelversion/build, and this folder is of course not writeable by the user. With the patch, a user-writable directory can be selected and DKMS seems to pick it up. But yes, I also have more questions than answers unfortunately... Maybe it is more of an issue with DKMS itself than with the kernel, in any way, DKMS needs a few fixes for Clang-built kernels, see [1]. [1] https://github.com/dell/dkms/issues/124 > > > > --- > > 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. > > > > -- > > 2.32.0 > > > > -- > Best Regards > Masahiro Yamada
