On 14.07.21 02:46, Masahiro Yamada wrote: > On Wed, Jul 14, 2021 at 1:41 AM 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. > > > Again, I do not understand. Example: 1. build and install a kernel+headers with Arch's own makepkg/pacman tools. 2. at the end of the install, dkms is automatically called to rebuild any out-of-tree modules like e.g. VirtualBox. 3. dkms fails because it tries to store the thinlto cache in a directory that it not user-writable (very possibly in the installed kernel headers directory under /usr/lib). 4. By explicitly selecting a place for the cache, e.g. /tmp, the dkms module rebuild succeeds. > > Is this fixing the root cause? If only I knew. I have very limited skills, and no IT or coding background. It's possible that this can be fixed also on dkms but I'm not sure. Currently, dkms does not do a compiler check (it only seems to know gcc) and it will fail unless explicitly told to use clang. e.g. by specifying 'CC=clang LD=ld.lld" etc. This has been reported to them. > > To me, it looks like > "Anyway, this worked for me" patch. At least one other person reported success by moving the cache to another place (see link). Admittedly, it looks the same way to me, I just wanted to get things to work and it's likely that there are better solutions to this problem, but AFAIR no one came forward. > > Besides, 'make clean' will never clean up the > cache directory. I can have a look at it again. > > > > > >> 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> >> --- >> Changes from v1 to v2: remove unneeded changes in scripts/Makefile >> >> Makefile | 5 +++-- >> arch/Kconfig | 10 ++++++++++ >> 2 files changed, 13 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 >> -- >> 2.32.0 >> > >
