diff mbox series

[v2,1/1] Kbuild, clang: add option for choosing a ThinLTO cache directory

Message ID a6eea2c4-6d90-3ddf-33d6-973d1ae917e7@mailbox.org (mailing list archive)
State New, archived
Headers show
Series [v2,1/1] Kbuild, clang: add option for choosing a ThinLTO cache directory | expand

Commit Message

Tor Vic July 13, 2021, 4:41 p.m. UTC 
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@mailbox.org>
---
Changes from v1 to v2: remove unneeded changes in scripts/Makefile

 Makefile     |  5 +++--
 arch/Kconfig | 10 ++++++++++
 2 files changed, 13 insertions(+), 2 deletions(-)

Comments

Masahiro Yamada July 14, 2021, 2:46 a.m. UTC | #1 
On Wed, Jul 14, 2021 at 1:41 AM Tor Vic <torvic9@mailbox.org> 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.

Is this fixing the root cause?

To me, it looks like
"Anyway, this worked for me" patch.

Besides, 'make clean' will never clean up the
cache directory.





> 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@mailbox.org>
> ---
> 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
>
Tor Vic July 14, 2021, 6:12 a.m. UTC | #2 
On 14.07.21 02:46, Masahiro Yamada wrote:
> On Wed, Jul 14, 2021 at 1:41 AM Tor Vic <torvic9@mailbox.org> 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@mailbox.org>
>> ---
>> 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
>>
> 
>
diff mbox series

Patch

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