2022-02-17 03:49:43

by Kees Cook

Subject: [PATCH] um: Allow builds with Clang

Add x86-64 target for Clang+um and update user-offsets.c to use
Clang-friendly assembler, similar to the fix from commit cf0c3e68aa81
("kbuild: fix asm-offset generation to work with clang").

This lets me run KUnit tests with Clang:

$ ./tools/testing/kunit/kunit.py config --make_options LLVM=1
...
$ ./tools/testing/kunit/kunit.py run --make_options LLVM=1
...

Cc: Jeff Dike <[email protected]>
Cc: Richard Weinberger <[email protected]>
Cc: Anton Ivanov <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Cc: Nick Desaulniers <[email protected]>
Cc: Nathan Chancellor <[email protected]>
Cc: David Gow <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Kees Cook <[email protected]>
---
arch/x86/um/user-offsets.c | 4 ++--
scripts/Makefile.clang | 1 +
2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/um/user-offsets.c b/arch/x86/um/user-offsets.c
index bae61554abcc..d9071827b515 100644
--- a/arch/x86/um/user-offsets.c
+++ b/arch/x86/um/user-offsets.c
@@ -10,10 +10,10 @@
#include <asm/types.h>

#define DEFINE(sym, val) \
- asm volatile("\n->" #sym " %0 " #val : : "i" (val))
+ asm volatile("\n.ascii \"->" #sym " %0 " #val "\"": : "i" (val))

#define DEFINE_LONGS(sym, val) \
- asm volatile("\n->" #sym " %0 " #val : : "i" (val/sizeof(unsigned long)))
+ asm volatile("\n.ascii \"->" #sym " %0 " #val "\"": : "i" (val/sizeof(unsigned long)))

void foo(void)
{
diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang
index 51fc23e2e9e5..857b23de51c6 100644
--- a/scripts/Makefile.clang
+++ b/scripts/Makefile.clang
@@ -10,6 +10,7 @@ CLANG_TARGET_FLAGS_powerpc := powerpc64le-linux-gnu
CLANG_TARGET_FLAGS_riscv := riscv64-linux-gnu
CLANG_TARGET_FLAGS_s390 := s390x-linux-gnu
CLANG_TARGET_FLAGS_x86 := x86_64-linux-gnu
+CLANG_TARGET_FLAGS_um := x86_64-linux-gnu
CLANG_TARGET_FLAGS := $(CLANG_TARGET_FLAGS_$(SRCARCH))

ifeq ($(CROSS_COMPILE),)
--
2.30.2

2022-02-17 05:59:25

by David Gow

Subject: Re: [PATCH] um: Allow builds with Clang

On Thu, Feb 17, 2022 at 8:28 AM Kees Cook <[email protected]> wrote:
>
> Add x86-64 target for Clang+um and update user-offsets.c to use
> Clang-friendly assembler, similar to the fix from commit cf0c3e68aa81
> ("kbuild: fix asm-offset generation to work with clang").
>
> This lets me run KUnit tests with Clang:
>
> $ ./tools/testing/kunit/kunit.py config --make_options LLVM=1
> ...
> $ ./tools/testing/kunit/kunit.py run --make_options LLVM=1
> ...
>
> Cc: Jeff Dike <[email protected]>
> Cc: Richard Weinberger <[email protected]>
> Cc: Anton Ivanov <[email protected]>
> Cc: Masahiro Yamada <[email protected]>
> Cc: Nick Desaulniers <[email protected]>
> Cc: Nathan Chancellor <[email protected]>
> Cc: David Gow <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Signed-off-by: Kees Cook <[email protected]>
> ---

Thanks, this worked fine for me, with one small note:

I get the following warning with clang (13.0.1) under UML (but not
under x86_64):
clang: warning: argument unused during compilation:
'-mno-global-merge' [-Wunused-command-line-argument]

It's not really a problem unless -Werror is enabled, though, so this
is still definitely an improvement over clang not working at all.

With that caveat, this is:
Tested-by: David Gow <[email protected]>

Cheers,
-- David

> arch/x86/um/user-offsets.c | 4 ++--
> scripts/Makefile.clang | 1 +
> 2 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/um/user-offsets.c b/arch/x86/um/user-offsets.c
> index bae61554abcc..d9071827b515 100644
> --- a/arch/x86/um/user-offsets.c
> +++ b/arch/x86/um/user-offsets.c
> @@ -10,10 +10,10 @@
> #include <asm/types.h>
>
> #define DEFINE(sym, val) \
> - asm volatile("\n->" #sym " %0 " #val : : "i" (val))
> + asm volatile("\n.ascii \"->" #sym " %0 " #val "\"": : "i" (val))
>
> #define DEFINE_LONGS(sym, val) \
> - asm volatile("\n->" #sym " %0 " #val : : "i" (val/sizeof(unsigned long)))
> + asm volatile("\n.ascii \"->" #sym " %0 " #val "\"": : "i" (val/sizeof(unsigned long)))
>
> void foo(void)
> {
> diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang
> index 51fc23e2e9e5..857b23de51c6 100644
> --- a/scripts/Makefile.clang
> +++ b/scripts/Makefile.clang
> @@ -10,6 +10,7 @@ CLANG_TARGET_FLAGS_powerpc := powerpc64le-linux-gnu
> CLANG_TARGET_FLAGS_riscv := riscv64-linux-gnu
> CLANG_TARGET_FLAGS_s390 := s390x-linux-gnu
> CLANG_TARGET_FLAGS_x86 := x86_64-linux-gnu
> +CLANG_TARGET_FLAGS_um := x86_64-linux-gnu
> CLANG_TARGET_FLAGS := $(CLANG_TARGET_FLAGS_$(SRCARCH))
>
> ifeq ($(CROSS_COMPILE),)
> --
> 2.30.2
>
> --
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2022-02-17 05:59:34

by Masahiro Yamada

Subject: Re: [PATCH] um: Allow builds with Clang

On Thu, Feb 17, 2022 at 9:28 AM Kees Cook <[email protected]> wrote:
>
> Add x86-64 target for Clang+um and update user-offsets.c to use
> Clang-friendly assembler, similar to the fix from commit cf0c3e68aa81
> ("kbuild: fix asm-offset generation to work with clang").
>
> This lets me run KUnit tests with Clang:
>
> $ ./tools/testing/kunit/kunit.py config --make_options LLVM=1
> ...
> $ ./tools/testing/kunit/kunit.py run --make_options LLVM=1
> ...
>
> Cc: Jeff Dike <[email protected]>
> Cc: Richard Weinberger <[email protected]>
> Cc: Anton Ivanov <[email protected]>
> Cc: Masahiro Yamada <[email protected]>
> Cc: Nick Desaulniers <[email protected]>
> Cc: Nathan Chancellor <[email protected]>
> Cc: David Gow <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Signed-off-by: Kees Cook <[email protected]>
> ---
> arch/x86/um/user-offsets.c | 4 ++--
> scripts/Makefile.clang | 1 +
> 2 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/um/user-offsets.c b/arch/x86/um/user-offsets.c
> index bae61554abcc..d9071827b515 100644
> --- a/arch/x86/um/user-offsets.c
> +++ b/arch/x86/um/user-offsets.c
> @@ -10,10 +10,10 @@
> #include <asm/types.h>
>
> #define DEFINE(sym, val) \
> - asm volatile("\n->" #sym " %0 " #val : : "i" (val))
> + asm volatile("\n.ascii \"->" #sym " %0 " #val "\"": : "i" (val))
>
> #define DEFINE_LONGS(sym, val) \
> - asm volatile("\n->" #sym " %0 " #val : : "i" (val/sizeof(unsigned long)))
> + asm volatile("\n.ascii \"->" #sym " %0 " #val "\"": : "i" (val/sizeof(unsigned long)))
>
> void foo(void)
> {
> diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang
> index 51fc23e2e9e5..857b23de51c6 100644
> --- a/scripts/Makefile.clang
> +++ b/scripts/Makefile.clang
> @@ -10,6 +10,7 @@ CLANG_TARGET_FLAGS_powerpc := powerpc64le-linux-gnu
> CLANG_TARGET_FLAGS_riscv := riscv64-linux-gnu
> CLANG_TARGET_FLAGS_s390 := s390x-linux-gnu
> CLANG_TARGET_FLAGS_x86 := x86_64-linux-gnu
> +CLANG_TARGET_FLAGS_um := x86_64-linux-gnu


Does this work for the i386 host?

UML supports i386 and x86_64 as the host architecture as of now,
but this always compiles UML for x86_64?







> CLANG_TARGET_FLAGS := $(CLANG_TARGET_FLAGS_$(SRCARCH))
>
> ifeq ($(CROSS_COMPILE),)
> --
> 2.30.2
>


--
Best Regards
Masahiro Yamada

2022-02-17 12:46:39

by Nathan Chancellor

Subject: Re: [PATCH] um: Allow builds with Clang

On Wed, Feb 16, 2022 at 04:28:43PM -0800, Kees Cook wrote:
> Add x86-64 target for Clang+um and update user-offsets.c to use
> Clang-friendly assembler, similar to the fix from commit cf0c3e68aa81

Clang-friendly assembly?

> ("kbuild: fix asm-offset generation to work with clang").
>
> This lets me run KUnit tests with Clang:
>
> $ ./tools/testing/kunit/kunit.py config --make_options LLVM=1
> ...
> $ ./tools/testing/kunit/kunit.py run --make_options LLVM=1
> ...
>
> Cc: Jeff Dike <[email protected]>
> Cc: Richard Weinberger <[email protected]>
> Cc: Anton Ivanov <[email protected]>
> Cc: Masahiro Yamada <[email protected]>
> Cc: Nick Desaulniers <[email protected]>
> Cc: Nathan Chancellor <[email protected]>
> Cc: David Gow <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Signed-off-by: Kees Cook <[email protected]>

I am not super familiar with UML but this seems reasonable.

Reviewed-by: Nathan Chancellor <[email protected]>

One small nit below if you have to send a v2, not sure it is worth it
otherwise.

> ---
> arch/x86/um/user-offsets.c | 4 ++--
> scripts/Makefile.clang | 1 +
> 2 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/um/user-offsets.c b/arch/x86/um/user-offsets.c
> index bae61554abcc..d9071827b515 100644
> --- a/arch/x86/um/user-offsets.c
> +++ b/arch/x86/um/user-offsets.c
> @@ -10,10 +10,10 @@
> #include <asm/types.h>
>
> #define DEFINE(sym, val) \
> - asm volatile("\n->" #sym " %0 " #val : : "i" (val))
> + asm volatile("\n.ascii \"->" #sym " %0 " #val "\"": : "i" (val))
>
> #define DEFINE_LONGS(sym, val) \
> - asm volatile("\n->" #sym " %0 " #val : : "i" (val/sizeof(unsigned long)))
> + asm volatile("\n.ascii \"->" #sym " %0 " #val "\"": : "i" (val/sizeof(unsigned long)))
>
> void foo(void)
> {
> diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang
> index 51fc23e2e9e5..857b23de51c6 100644
> --- a/scripts/Makefile.clang
> +++ b/scripts/Makefile.clang
> @@ -10,6 +10,7 @@ CLANG_TARGET_FLAGS_powerpc := powerpc64le-linux-gnu
> CLANG_TARGET_FLAGS_riscv := riscv64-linux-gnu
> CLANG_TARGET_FLAGS_s390 := s390x-linux-gnu
> CLANG_TARGET_FLAGS_x86 := x86_64-linux-gnu
> +CLANG_TARGET_FLAGS_um := x86_64-linux-gnu

It might be nice to keep this in alphabetical order.

> CLANG_TARGET_FLAGS := $(CLANG_TARGET_FLAGS_$(SRCARCH))
>
> ifeq ($(CROSS_COMPILE),)
> --
> 2.30.2
>
>

2022-02-17 21:04:21

by Nathan Chancellor

Subject: Re: [PATCH] um: Allow builds with Clang

On Thu, Feb 17, 2022 at 01:54:58PM +0900, Masahiro Yamada wrote:
> On Thu, Feb 17, 2022 at 9:28 AM Kees Cook <[email protected]> wrote:
> >
> > Add x86-64 target for Clang+um and update user-offsets.c to use
> > Clang-friendly assembler, similar to the fix from commit cf0c3e68aa81
> > ("kbuild: fix asm-offset generation to work with clang").
> >
> > This lets me run KUnit tests with Clang:
> >
> > $ ./tools/testing/kunit/kunit.py config --make_options LLVM=1
> > ...
> > $ ./tools/testing/kunit/kunit.py run --make_options LLVM=1
> > ...
> >
> > Cc: Jeff Dike <[email protected]>
> > Cc: Richard Weinberger <[email protected]>
> > Cc: Anton Ivanov <[email protected]>
> > Cc: Masahiro Yamada <[email protected]>
> > Cc: Nick Desaulniers <[email protected]>
> > Cc: Nathan Chancellor <[email protected]>
> > Cc: David Gow <[email protected]>
> > Cc: [email protected]
> > Cc: [email protected]
> > Cc: [email protected]
> > Cc: [email protected]
> > Cc: [email protected]
> > Signed-off-by: Kees Cook <[email protected]>
> > ---
> > arch/x86/um/user-offsets.c | 4 ++--
> > scripts/Makefile.clang | 1 +
> > 2 files changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/um/user-offsets.c b/arch/x86/um/user-offsets.c
> > index bae61554abcc..d9071827b515 100644
> > --- a/arch/x86/um/user-offsets.c
> > +++ b/arch/x86/um/user-offsets.c
> > @@ -10,10 +10,10 @@
> > #include <asm/types.h>
> >
> > #define DEFINE(sym, val) \
> > - asm volatile("\n->" #sym " %0 " #val : : "i" (val))
> > + asm volatile("\n.ascii \"->" #sym " %0 " #val "\"": : "i" (val))
> >
> > #define DEFINE_LONGS(sym, val) \
> > - asm volatile("\n->" #sym " %0 " #val : : "i" (val/sizeof(unsigned long)))
> > + asm volatile("\n.ascii \"->" #sym " %0 " #val "\"": : "i" (val/sizeof(unsigned long)))
> >
> > void foo(void)
> > {
> > diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang
> > index 51fc23e2e9e5..857b23de51c6 100644
> > --- a/scripts/Makefile.clang
> > +++ b/scripts/Makefile.clang
> > @@ -10,6 +10,7 @@ CLANG_TARGET_FLAGS_powerpc := powerpc64le-linux-gnu
> > CLANG_TARGET_FLAGS_riscv := riscv64-linux-gnu
> > CLANG_TARGET_FLAGS_s390 := s390x-linux-gnu
> > CLANG_TARGET_FLAGS_x86 := x86_64-linux-gnu
> > +CLANG_TARGET_FLAGS_um := x86_64-linux-gnu
>
>
> Does this work for the i386 host?
>
> UML supports i386 and x86_64 as the host architecture as of now,
> but this always compiles UML for x86_64?

I think the current code will work because arch/x86/Makefile.um includes
-m32 for CONFIG_X86_32, which will implicitly change x86_64-linux-gnu
into a 32-bit target triple:

$ echo | clang --target=x86_64-linux-gnu -x c -c -o test.o -

$ file test.o
test.o: ELF 64-bit LSB relocatable, x86-64, version 1 (SYSV), not stripped

$ echo | clang --target=x86_64-linux-gnu -m32 -x c -c -o test.o -

$ file test.o
test.o: ELF 32-bit LSB relocatable, Intel 80386, version 1 (SYSV), not stripped

In fact, we rely on this for ARCH=i386 LLVM=1 right now, as it uses
x86_64-linux-gnu for the target flag.

While UML only supports x86, maybe it is worth using SUBARCH instead of
hardcoding the triple? No strong opinion around that though.

diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang
index 51fc23e2e9e5..87285b76adb2 100644
--- a/scripts/Makefile.clang
+++ b/scripts/Makefile.clang
@@ -10,6 +10,7 @@ CLANG_TARGET_FLAGS_powerpc := powerpc64le-linux-gnu
CLANG_TARGET_FLAGS_riscv := riscv64-linux-gnu
CLANG_TARGET_FLAGS_s390 := s390x-linux-gnu
CLANG_TARGET_FLAGS_x86 := x86_64-linux-gnu
+CLANG_TARGET_FLAGS_um := $(CLANG_TARGET_FLAGS_$(SUBARCH))
CLANG_TARGET_FLAGS := $(CLANG_TARGET_FLAGS_$(SRCARCH))

ifeq ($(CROSS_COMPILE),)

> > CLANG_TARGET_FLAGS := $(CLANG_TARGET_FLAGS_$(SRCARCH))
> >
> > ifeq ($(CROSS_COMPILE),)
> > --
> > 2.30.2
> >
>
>
> --
> Best Regards
> Masahiro Yamada

2022-02-18 02:20:46

by Masahiro Yamada

Subject: Re: [PATCH] um: Allow builds with Clang

On Fri, Feb 18, 2022 at 2:41 AM Nathan Chancellor <[email protected]> wrote:
>
> On Thu, Feb 17, 2022 at 01:54:58PM +0900, Masahiro Yamada wrote:
> > On Thu, Feb 17, 2022 at 9:28 AM Kees Cook <[email protected]> wrote:
> > >
> > > Add x86-64 target for Clang+um and update user-offsets.c to use
> > > Clang-friendly assembler, similar to the fix from commit cf0c3e68aa81
> > > ("kbuild: fix asm-offset generation to work with clang").
> > >
> > > This lets me run KUnit tests with Clang:
> > >
> > > $ ./tools/testing/kunit/kunit.py config --make_options LLVM=1
> > > ...
> > > $ ./tools/testing/kunit/kunit.py run --make_options LLVM=1
> > > ...
> > >
> > > Cc: Jeff Dike <[email protected]>
> > > Cc: Richard Weinberger <[email protected]>
> > > Cc: Anton Ivanov <[email protected]>
> > > Cc: Masahiro Yamada <[email protected]>
> > > Cc: Nick Desaulniers <[email protected]>
> > > Cc: Nathan Chancellor <[email protected]>
> > > Cc: David Gow <[email protected]>
> > > Cc: [email protected]
> > > Cc: [email protected]
> > > Cc: [email protected]
> > > Cc: [email protected]
> > > Cc: [email protected]
> > > Signed-off-by: Kees Cook <[email protected]>
> > > ---
> > > arch/x86/um/user-offsets.c | 4 ++--
> > > scripts/Makefile.clang | 1 +
> > > 2 files changed, 3 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/arch/x86/um/user-offsets.c b/arch/x86/um/user-offsets.c
> > > index bae61554abcc..d9071827b515 100644
> > > --- a/arch/x86/um/user-offsets.c
> > > +++ b/arch/x86/um/user-offsets.c
> > > @@ -10,10 +10,10 @@
> > > #include <asm/types.h>
> > >
> > > #define DEFINE(sym, val) \
> > > - asm volatile("\n->" #sym " %0 " #val : : "i" (val))
> > > + asm volatile("\n.ascii \"->" #sym " %0 " #val "\"": : "i" (val))
> > >
> > > #define DEFINE_LONGS(sym, val) \
> > > - asm volatile("\n->" #sym " %0 " #val : : "i" (val/sizeof(unsigned long)))
> > > + asm volatile("\n.ascii \"->" #sym " %0 " #val "\"": : "i" (val/sizeof(unsigned long)))
> > >
> > > void foo(void)
> > > {
> > > diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang
> > > index 51fc23e2e9e5..857b23de51c6 100644
> > > --- a/scripts/Makefile.clang
> > > +++ b/scripts/Makefile.clang
> > > @@ -10,6 +10,7 @@ CLANG_TARGET_FLAGS_powerpc := powerpc64le-linux-gnu
> > > CLANG_TARGET_FLAGS_riscv := riscv64-linux-gnu
> > > CLANG_TARGET_FLAGS_s390 := s390x-linux-gnu
> > > CLANG_TARGET_FLAGS_x86 := x86_64-linux-gnu
> > > +CLANG_TARGET_FLAGS_um := x86_64-linux-gnu
> >
> >
> > Does this work for the i386 host?
> >
> > UML supports i386 and x86_64 as the host architecture as of now,
> > but this always compiles UML for x86_64?
>
> I think the current code will work because arch/x86/Makefile.um includes
> -m32 for CONFIG_X86_32, which will implicitly change x86_64-linux-gnu
> into a 32-bit target triple:

Ah, you are right!


>
> $ echo | clang --target=x86_64-linux-gnu -x c -c -o test.o -
>
> $ file test.o
> test.o: ELF 64-bit LSB relocatable, x86-64, version 1 (SYSV), not stripped
>
> $ echo | clang --target=x86_64-linux-gnu -m32 -x c -c -o test.o -
>
> $ file test.o
> test.o: ELF 32-bit LSB relocatable, Intel 80386, version 1 (SYSV), not stripped
>
> In fact, we rely on this for ARCH=i386 LLVM=1 right now, as it uses
> x86_64-linux-gnu for the target flag.
>
> While UML only supports x86, maybe it is worth using SUBARCH instead of
> hardcoding the triple? No strong opinion around that though.
>
> diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang
> index 51fc23e2e9e5..87285b76adb2 100644
> --- a/scripts/Makefile.clang
> +++ b/scripts/Makefile.clang
> @@ -10,6 +10,7 @@ CLANG_TARGET_FLAGS_powerpc := powerpc64le-linux-gnu
> CLANG_TARGET_FLAGS_riscv := riscv64-linux-gnu
> CLANG_TARGET_FLAGS_s390 := s390x-linux-gnu
> CLANG_TARGET_FLAGS_x86 := x86_64-linux-gnu
> +CLANG_TARGET_FLAGS_um := $(CLANG_TARGET_FLAGS_$(SUBARCH))


LGTM.

I also thought of not passing --target at all for ARCH=um, but
we decided to override --target all the time (for reproducibility?).
Anyway, Nathan's way is clean, and looks OK to me.







> CLANG_TARGET_FLAGS := $(CLANG_TARGET_FLAGS_$(SRCARCH))
>
> ifeq ($(CROSS_COMPILE),)
>
> > > CLANG_TARGET_FLAGS := $(CLANG_TARGET_FLAGS_$(SRCARCH))
> > >
> > > ifeq ($(CROSS_COMPILE),)
> > > --
> > > 2.30.2
> > >
> >
> >
> > --
> > Best Regards
> > Masahiro Yamada



--
Best Regards
Masahiro Yamada