Commit b33fff07e3e3 ("x86, build: allow LTO to be selected") added a
couple of '-plugin-opt=' flags to KBUILD_LDFLAGS because the code model
and stack alignment are not stored in LLVM bitcode. However, these flags
were added to KBUILD_LDFLAGS prior to the emulation flag assignment,
which uses ':=', so they were overwritten and never added to $(LD)
invocations. The absence of these flags caused misalignment issues in
the AMDGPU driver when compiling with CONFIG_LTO_CLANG, resulting in
general protection faults.
Shuffle the assignment below the initial one so that the flags are
properly passed along and all of the linker flags stay together.
At the same time, avoid any future issues with clobbering flags by
changing the emulation flag assignment to '+=' since KBUILD_LDFLAGS is
already defined with ':=' in the main Makefile before being exported for
modification here as a result of commit ce99d0bf312d ("kbuild: clear
LDFLAGS in the top Makefile").
Cc: [email protected]
Fixes: b33fff07e3e3 ("x86, build: allow LTO to be selected")
Link: https://github.com/ClangBuiltLinux/linux/issues/1374
Reported-by: Anthony Ruhier <[email protected]>
Tested-by: Anthony Ruhier <[email protected]>
Signed-off-by: Nathan Chancellor <[email protected]>
---
arch/x86/Makefile | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index c77c5d8a7b3e..307529417021 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -178,11 +178,6 @@ ifeq ($(ACCUMULATE_OUTGOING_ARGS), 1)
KBUILD_CFLAGS += $(call cc-option,-maccumulate-outgoing-args,)
endif
-ifdef CONFIG_LTO_CLANG
-KBUILD_LDFLAGS += -plugin-opt=-code-model=kernel \
- -plugin-opt=-stack-alignment=$(if $(CONFIG_X86_32),4,8)
-endif
-
# Workaround for a gcc prelease that unfortunately was shipped in a suse release
KBUILD_CFLAGS += -Wno-sign-compare
#
@@ -202,7 +197,12 @@ ifdef CONFIG_RETPOLINE
endif
endif
-KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE)
+KBUILD_LDFLAGS += -m elf_$(UTS_MACHINE)
+
+ifdef CONFIG_LTO_CLANG
+KBUILD_LDFLAGS += -plugin-opt=-code-model=kernel \
+ -plugin-opt=-stack-alignment=$(if $(CONFIG_X86_32),4,8)
+endif
ifdef CONFIG_X86_NEED_RELOCS
LDFLAGS_vmlinux := --emit-relocs --discard-none
base-commit: d07f6ca923ea0927a1024dfccafc5b53b61cfecc
--
2.32.0.rc0
On Tue, May 18, 2021 at 12:01 PM Nathan Chancellor <[email protected]> wrote:
>
> Commit b33fff07e3e3 ("x86, build: allow LTO to be selected") added a
> couple of '-plugin-opt=' flags to KBUILD_LDFLAGS because the code model
> and stack alignment are not stored in LLVM bitcode. However, these flags
> were added to KBUILD_LDFLAGS prior to the emulation flag assignment,
> which uses ':=', so they were overwritten and never added to $(LD)
> invocations. The absence of these flags caused misalignment issues in
> the AMDGPU driver when compiling with CONFIG_LTO_CLANG, resulting in
> general protection faults.
>
> Shuffle the assignment below the initial one so that the flags are
> properly passed along and all of the linker flags stay together.
>
> At the same time, avoid any future issues with clobbering flags by
> changing the emulation flag assignment to '+=' since KBUILD_LDFLAGS is
> already defined with ':=' in the main Makefile before being exported for
> modification here as a result of commit ce99d0bf312d ("kbuild: clear
> LDFLAGS in the top Makefile").
Thanks for the patch file. I will need to be more wary of `:=`
operator in kbuild changes in the future.
Ideally, we should encode these two flags in LLVM's IR so that we
don't need to respecify them when restarting optimizations from the
linker during LTO. I've filed
https://github.com/ClangBuiltLinux/linux/issues/1377 to follow up on
that idea.
Reviewed-by: Nick Desaulniers <[email protected]>
>
> Cc: [email protected]
> Fixes: b33fff07e3e3 ("x86, build: allow LTO to be selected")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1374
> Reported-by: Anthony Ruhier <[email protected]>
> Tested-by: Anthony Ruhier <[email protected]>
> Signed-off-by: Nathan Chancellor <[email protected]>
> ---
> arch/x86/Makefile | 12 ++++++------
> 1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index c77c5d8a7b3e..307529417021 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -178,11 +178,6 @@ ifeq ($(ACCUMULATE_OUTGOING_ARGS), 1)
> KBUILD_CFLAGS += $(call cc-option,-maccumulate-outgoing-args,)
> endif
>
> -ifdef CONFIG_LTO_CLANG
> -KBUILD_LDFLAGS += -plugin-opt=-code-model=kernel \
> - -plugin-opt=-stack-alignment=$(if $(CONFIG_X86_32),4,8)
> -endif
> -
> # Workaround for a gcc prelease that unfortunately was shipped in a suse release
> KBUILD_CFLAGS += -Wno-sign-compare
> #
> @@ -202,7 +197,12 @@ ifdef CONFIG_RETPOLINE
> endif
> endif
>
> -KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE)
> +KBUILD_LDFLAGS += -m elf_$(UTS_MACHINE)
> +
> +ifdef CONFIG_LTO_CLANG
> +KBUILD_LDFLAGS += -plugin-opt=-code-model=kernel \
> + -plugin-opt=-stack-alignment=$(if $(CONFIG_X86_32),4,8)
> +endif
>
> ifdef CONFIG_X86_NEED_RELOCS
> LDFLAGS_vmlinux := --emit-relocs --discard-none
>
> base-commit: d07f6ca923ea0927a1024dfccafc5b53b61cfecc
> --
> 2.32.0.rc0
>
--
Thanks,
~Nick Desaulniers
The following commit has been merged into the x86/urgent branch of tip:
Commit-ID: 0024430e920f2900654ad83cd081cf52e02a3ef5
Gitweb: https://git.kernel.org/tip/0024430e920f2900654ad83cd081cf52e02a3ef5
Author: Nathan Chancellor <[email protected]>
AuthorDate: Tue, 18 May 2021 12:01:06 -07:00
Committer: Ingo Molnar <[email protected]>
CommitterDate: Wed, 19 May 2021 13:05:53 +02:00
x86/build: Fix location of '-plugin-opt=' flags
Commit b33fff07e3e3 ("x86, build: allow LTO to be selected") added a
couple of '-plugin-opt=' flags to KBUILD_LDFLAGS because the code model
and stack alignment are not stored in LLVM bitcode.
However, these flags were added to KBUILD_LDFLAGS prior to the
emulation flag assignment, which uses ':=', so they were overwritten
and never added to $(LD) invocations.
The absence of these flags caused misalignment issues in the
AMDGPU driver when compiling with CONFIG_LTO_CLANG, resulting in
general protection faults.
Shuffle the assignment below the initial one so that the flags are
properly passed along and all of the linker flags stay together.
At the same time, avoid any future issues with clobbering flags by
changing the emulation flag assignment to '+=' since KBUILD_LDFLAGS is
already defined with ':=' in the main Makefile before being exported for
modification here as a result of commit:
ce99d0bf312d ("kbuild: clear LDFLAGS in the top Makefile")
Fixes: b33fff07e3e3 ("x86, build: allow LTO to be selected")
Reported-by: Anthony Ruhier <[email protected]>
Signed-off-by: Nathan Chancellor <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Tested-by: Anthony Ruhier <[email protected]>
Cc: [email protected]
Link: https://github.com/ClangBuiltLinux/linux/issues/1374
Link: https://lore.kernel.org/r/[email protected]
---
arch/x86/Makefile | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index c77c5d8..3075294 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -178,11 +178,6 @@ ifeq ($(ACCUMULATE_OUTGOING_ARGS), 1)
KBUILD_CFLAGS += $(call cc-option,-maccumulate-outgoing-args,)
endif
-ifdef CONFIG_LTO_CLANG
-KBUILD_LDFLAGS += -plugin-opt=-code-model=kernel \
- -plugin-opt=-stack-alignment=$(if $(CONFIG_X86_32),4,8)
-endif
-
# Workaround for a gcc prelease that unfortunately was shipped in a suse release
KBUILD_CFLAGS += -Wno-sign-compare
#
@@ -202,7 +197,12 @@ ifdef CONFIG_RETPOLINE
endif
endif
-KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE)
+KBUILD_LDFLAGS += -m elf_$(UTS_MACHINE)
+
+ifdef CONFIG_LTO_CLANG
+KBUILD_LDFLAGS += -plugin-opt=-code-model=kernel \
+ -plugin-opt=-stack-alignment=$(if $(CONFIG_X86_32),4,8)
+endif
ifdef CONFIG_X86_NEED_RELOCS
LDFLAGS_vmlinux := --emit-relocs --discard-none
On Tue, 18 May 2021 12:01:06 -0700, Nathan Chancellor wrote:
> Commit b33fff07e3e3 ("x86, build: allow LTO to be selected") added a
> couple of '-plugin-opt=' flags to KBUILD_LDFLAGS because the code model
> and stack alignment are not stored in LLVM bitcode. However, these flags
> were added to KBUILD_LDFLAGS prior to the emulation flag assignment,
> which uses ':=', so they were overwritten and never added to $(LD)
> invocations. The absence of these flags caused misalignment issues in
> the AMDGPU driver when compiling with CONFIG_LTO_CLANG, resulting in
> general protection faults.
>
> [...]
(I've slightly adjusted the title.)
Applied to for-next/clang/features, thanks!
[1/1] x86: lto: Fix location of '-plugin-opt=' flags
https://git.kernel.org/kees/c/5d6c8592ee5f
--
Kees Cook
On Fri, May 21, 2021 at 10:59:10AM -0700, Kees Cook wrote:
> On Tue, 18 May 2021 12:01:06 -0700, Nathan Chancellor wrote:
> > Commit b33fff07e3e3 ("x86, build: allow LTO to be selected") added a
> > couple of '-plugin-opt=' flags to KBUILD_LDFLAGS because the code model
> > and stack alignment are not stored in LLVM bitcode. However, these flags
> > were added to KBUILD_LDFLAGS prior to the emulation flag assignment,
> > which uses ':=', so they were overwritten and never added to $(LD)
> > invocations. The absence of these flags caused misalignment issues in
> > the AMDGPU driver when compiling with CONFIG_LTO_CLANG, resulting in
> > general protection faults.
> >
> > [...]
>
> (I've slightly adjusted the title.)
>
> Applied to for-next/clang/features, thanks!
>
> [1/1] x86: lto: Fix location of '-plugin-opt=' flags
> https://git.kernel.org/kees/c/5d6c8592ee5f
>
Ingo picked this up in x86/urgent so you should not need to carry it.
https://git.kernel.org/tip/0024430e920f2900654ad83cd081cf52e02a3ef5
Cheers,
Nathan
On Fri, May 21, 2021 at 11:31:54AM -0700, Nathan Chancellor wrote:
> On Fri, May 21, 2021 at 10:59:10AM -0700, Kees Cook wrote:
> > On Tue, 18 May 2021 12:01:06 -0700, Nathan Chancellor wrote:
> > > Commit b33fff07e3e3 ("x86, build: allow LTO to be selected") added a
> > > couple of '-plugin-opt=' flags to KBUILD_LDFLAGS because the code model
> > > and stack alignment are not stored in LLVM bitcode. However, these flags
> > > were added to KBUILD_LDFLAGS prior to the emulation flag assignment,
> > > which uses ':=', so they were overwritten and never added to $(LD)
> > > invocations. The absence of these flags caused misalignment issues in
> > > the AMDGPU driver when compiling with CONFIG_LTO_CLANG, resulting in
> > > general protection faults.
> > >
> > > [...]
> >
> > (I've slightly adjusted the title.)
> >
> > Applied to for-next/clang/features, thanks!
> >
> > [1/1] x86: lto: Fix location of '-plugin-opt=' flags
> > https://git.kernel.org/kees/c/5d6c8592ee5f
> >
>
> Ingo picked this up in x86/urgent so you should not need to carry it.
>
> https://git.kernel.org/tip/0024430e920f2900654ad83cd081cf52e02a3ef5
Ah-ha, thanks! I didn't see a reply on the thread.
--
Kees Cook