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  3. [PATCH v2 00/10] kbuild: userprogs: introduce architecture-specific CC_CAN_LINK and userprog flags
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[PATCH v2 03/10] kbuild: allow architectures to override CC_CAN_LINK

Thomas Weißschuh posted 10 patches 2 months ago
There is a newer version of this series
[PATCH v2 03/10] kbuild: allow architectures to override CC_CAN_LINK
Posted by Thomas Weißschuh 2 months ago 
The generic test for CC_CAN_LINK assumes that all architectures use -m32
and -m64 to switch between 32-bit and 64-bit compilation. This is overly
simplistic. Architectures may use other flags (-mabi, -m31, etc.) or may
also require byte order handling (-mlittle-endian, -EL). Expressing all
of the different possibilities will be very complicated and brittle.
Instead allow architectures to supply their own logic which will be
easy to understand and evolve.

Both the boolean ARCH_HAS_CC_CAN_LINK and the string ARCH_USERFLAGS need
to be implemented as kconfig does not allow the reuse of string options.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
---
 Makefile     | 13 +++++++++++--
 init/Kconfig |  4 ++++
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index 17cfa11ca7163aa3297101ceb3c9e85f4878f12d..26e5bca534e27034c355939bca4c90db435ecdbd 100644
--- a/Makefile
+++ b/Makefile
@@ -1134,8 +1134,17 @@ ifneq ($(CONFIG_ARCH_VMLINUX_NEEDS_RELOCS),)
 LDFLAGS_vmlinux	+= --emit-relocs --discard-none
 endif
 
-# Align the bit size of userspace programs with the kernel
-USERFLAGS_FROM_KERNEL := -m32 -m64 --target=%
+# Align the architecture of userspace programs with the kernel
+USERFLAGS_FROM_KERNEL := --target=%
+
+ifdef CONFIG_ARCH_USERPROGS_CFLAGS
+KBUILD_USERCFLAGS += $(CONFIG_ARCH_USERFLAGS)
+KBUILD_USERLDFLAGS += $(CONFIG_ARCH_USERFLAGS)
+else
+# If not overridden also inherit the bit size
+USERFLAGS_FROM_KERNEL += -m32 -m64
+endif
+
 KBUILD_USERCFLAGS  += $(filter $(USERFLAGS_FROM_KERNEL), $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS))
 KBUILD_USERLDFLAGS += $(filter $(USERFLAGS_FROM_KERNEL), $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS))
 
diff --git a/init/Kconfig b/init/Kconfig
index 7b722e714d5c5a0580467914b226dc0700ec0797..4a2ae3cfbf26525a60936d9b29a74ef4319ba3a5 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -82,8 +82,12 @@ config RUSTC_LLVM_VERSION
 	int
 	default $(rustc-llvm-version)
 
+config ARCH_HAS_CC_CAN_LINK
+	bool
+
 config CC_CAN_LINK
 	bool
+	default ARCH_CC_CAN_LINK if ARCH_HAS_CC_CAN_LINK
 	default $(cc_can_link_user,$(m64-flag)) if 64BIT
 	default $(cc_can_link_user,$(m32-flag))
 

-- 
2.51.0
Re: [PATCH v2 03/10] kbuild: allow architectures to override CC_CAN_LINK
Posted by Nathan Chancellor 1 month ago 
On Tue, Oct 14, 2025 at 03:05:18PM +0200, Thomas Weißschuh wrote:
> The generic test for CC_CAN_LINK assumes that all architectures use -m32
> and -m64 to switch between 32-bit and 64-bit compilation. This is overly
> simplistic. Architectures may use other flags (-mabi, -m31, etc.) or may
> also require byte order handling (-mlittle-endian, -EL). Expressing all
> of the different possibilities will be very complicated and brittle.
> Instead allow architectures to supply their own logic which will be
> easy to understand and evolve.
> 
> Both the boolean ARCH_HAS_CC_CAN_LINK and the string ARCH_USERFLAGS need
> to be implemented as kconfig does not allow the reuse of string options.
> 
> Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>

Modulo Nicolas's existing comment about CONFIG_ARCH_USERPROGS_CFLAGS:

Reviewed-by: Nathan Chancellor <nathan@kernel.org>

> ---
>  Makefile     | 13 +++++++++++--
>  init/Kconfig |  4 ++++
>  2 files changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index 17cfa11ca7163aa3297101ceb3c9e85f4878f12d..26e5bca534e27034c355939bca4c90db435ecdbd 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1134,8 +1134,17 @@ ifneq ($(CONFIG_ARCH_VMLINUX_NEEDS_RELOCS),)
>  LDFLAGS_vmlinux	+= --emit-relocs --discard-none
>  endif
>  
> -# Align the bit size of userspace programs with the kernel
> -USERFLAGS_FROM_KERNEL := -m32 -m64 --target=%
> +# Align the architecture of userspace programs with the kernel
> +USERFLAGS_FROM_KERNEL := --target=%
> +
> +ifdef CONFIG_ARCH_USERPROGS_CFLAGS
> +KBUILD_USERCFLAGS += $(CONFIG_ARCH_USERFLAGS)
> +KBUILD_USERLDFLAGS += $(CONFIG_ARCH_USERFLAGS)
> +else
> +# If not overridden also inherit the bit size
> +USERFLAGS_FROM_KERNEL += -m32 -m64
> +endif
> +
>  KBUILD_USERCFLAGS  += $(filter $(USERFLAGS_FROM_KERNEL), $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS))
>  KBUILD_USERLDFLAGS += $(filter $(USERFLAGS_FROM_KERNEL), $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS))
>  
> diff --git a/init/Kconfig b/init/Kconfig
> index 7b722e714d5c5a0580467914b226dc0700ec0797..4a2ae3cfbf26525a60936d9b29a74ef4319ba3a5 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -82,8 +82,12 @@ config RUSTC_LLVM_VERSION
>  	int
>  	default $(rustc-llvm-version)
>  
> +config ARCH_HAS_CC_CAN_LINK
> +	bool
> +
>  config CC_CAN_LINK
>  	bool
> +	default ARCH_CC_CAN_LINK if ARCH_HAS_CC_CAN_LINK
>  	default $(cc_can_link_user,$(m64-flag)) if 64BIT
>  	default $(cc_can_link_user,$(m32-flag))
>  
> 
> -- 
> 2.51.0
>
Re: [PATCH v2 03/10] kbuild: allow architectures to override CC_CAN_LINK
Posted by Nicolas Schier 1 month, 1 week ago 
On Tue, Oct 14, 2025 at 03:05:18PM +0200, Thomas Weißschuh wrote:
> The generic test for CC_CAN_LINK assumes that all architectures use -m32
> and -m64 to switch between 32-bit and 64-bit compilation. This is overly
> simplistic. Architectures may use other flags (-mabi, -m31, etc.) or may
> also require byte order handling (-mlittle-endian, -EL). Expressing all
> of the different possibilities will be very complicated and brittle.
> Instead allow architectures to supply their own logic which will be
> easy to understand and evolve.
> 
> Both the boolean ARCH_HAS_CC_CAN_LINK and the string ARCH_USERFLAGS need
> to be implemented as kconfig does not allow the reuse of string options.
> 
> Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
> ---
>  Makefile     | 13 +++++++++++--
>  init/Kconfig |  4 ++++
>  2 files changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index 17cfa11ca7163aa3297101ceb3c9e85f4878f12d..26e5bca534e27034c355939bca4c90db435ecdbd 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1134,8 +1134,17 @@ ifneq ($(CONFIG_ARCH_VMLINUX_NEEDS_RELOCS),)
>  LDFLAGS_vmlinux	+= --emit-relocs --discard-none
>  endif
>  
> -# Align the bit size of userspace programs with the kernel
> -USERFLAGS_FROM_KERNEL := -m32 -m64 --target=%
> +# Align the architecture of userspace programs with the kernel
> +USERFLAGS_FROM_KERNEL := --target=%
> +
> +ifdef CONFIG_ARCH_USERPROGS_CFLAGS

Is this some left-over from a previous version?

s/CONFIG_ARCH_USERPROGS_CFLAGS/CONFIG_ARCH_USERFLAGS/

Kind regards,
Nicolas
Re: [PATCH v2 03/10] kbuild: allow architectures to override CC_CAN_LINK
Posted by Thomas Weißschuh 1 month ago 
On Wed, Nov 12, 2025 at 08:56:12PM +0100, Nicolas Schier wrote:
> On Tue, Oct 14, 2025 at 03:05:18PM +0200, Thomas Weißschuh wrote:
> > The generic test for CC_CAN_LINK assumes that all architectures use -m32
> > and -m64 to switch between 32-bit and 64-bit compilation. This is overly
> > simplistic. Architectures may use other flags (-mabi, -m31, etc.) or may
> > also require byte order handling (-mlittle-endian, -EL). Expressing all
> > of the different possibilities will be very complicated and brittle.
> > Instead allow architectures to supply their own logic which will be
> > easy to understand and evolve.
> > 
> > Both the boolean ARCH_HAS_CC_CAN_LINK and the string ARCH_USERFLAGS need
> > to be implemented as kconfig does not allow the reuse of string options.
> > 
> > Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
> > ---
> >  Makefile     | 13 +++++++++++--
> >  init/Kconfig |  4 ++++
> >  2 files changed, 15 insertions(+), 2 deletions(-)
> > 
> > diff --git a/Makefile b/Makefile
> > index 17cfa11ca7163aa3297101ceb3c9e85f4878f12d..26e5bca534e27034c355939bca4c90db435ecdbd 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -1134,8 +1134,17 @@ ifneq ($(CONFIG_ARCH_VMLINUX_NEEDS_RELOCS),)
> >  LDFLAGS_vmlinux	+= --emit-relocs --discard-none
> >  endif
> >  
> > -# Align the bit size of userspace programs with the kernel
> > -USERFLAGS_FROM_KERNEL := -m32 -m64 --target=%
> > +# Align the architecture of userspace programs with the kernel
> > +USERFLAGS_FROM_KERNEL := --target=%
> > +
> > +ifdef CONFIG_ARCH_USERPROGS_CFLAGS
> 
> Is this some left-over from a previous version?
> 
> s/CONFIG_ARCH_USERPROGS_CFLAGS/CONFIG_ARCH_USERFLAGS/

Indeed. Thanks.

Patchew 2.1-devel-b67e4c2

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