2022-07-20 13:29:11

by Dimitri John Ledkov

Subject: [PATCH] kbuild: introduce $(GCC) variable for path-prefix or version-suffix

Introduce $(GCC) variable with similar semantics to $(LLVM) for
setting path-prefix or version-suffix.

Currently to correctly and consistently use gcc-10 on Ubuntu 20.04
LTS, to cross compile a kernel one has to do:

$ make ... CROSS_COMPILE=riscv64-linux-gnu- \
CC=riscv64-linux-gnu-gcc-10 \
HOSTCC=gcc-10 \
HOSTCXX=g++-10

With this change

$ make ... CROSS_COMPILE=riscv64-linux-gnu- GCC=-10

is sufficient to correctly select a consistent CC/HOSTCC/HOSTCXX set.

Similarly GCC=/path/to/unpacked/toolchains/ can be used to select
toolchain outside of PATH.

Update documentation for LLVM variable, and mention that GCC variable
can be used in a similar fashion to set path-prefix, or
version-suffix.

Signed-off-by: Dimitri John Ledkov <[email protected]>
---
Documentation/kbuild/kbuild.rst | 12 ++++++++++--
Makefile | 12 +++++++++---
tools/testing/selftests/lib.mk | 2 +-
3 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/Documentation/kbuild/kbuild.rst b/Documentation/kbuild/kbuild.rst
index ef19b9c13523..6382b082018e 100644
--- a/Documentation/kbuild/kbuild.rst
+++ b/Documentation/kbuild/kbuild.rst
@@ -276,5 +276,13 @@ whoami and host, respectively.

LLVM
----
-If this variable is set to 1, Kbuild will use Clang and LLVM utilities instead
-of GCC and GNU binutils to build the kernel.
+If this variable is set to 1, Kbuild will use Clang and LLVM utilities
+instead of GCC and GNU binutils to build the kernel. It can also be
+used to set a path prefix, or a version suffix, see "Building
+Linux with Clang/LLVM".
+
+GCC
+---
+This variable can be used similar to LLVM variable above to set a path
+prefix, or a version suffix for GNU Toolchain binaries. See examples
+in "Building Linux with Clang/LLVM".
diff --git a/Makefile b/Makefile
index 00fd80c5dd6e..e7bd0b572b14 100644
--- a/Makefile
+++ b/Makefile
@@ -433,8 +433,14 @@ endif
HOSTCC = $(LLVM_PREFIX)clang$(LLVM_SUFFIX)
HOSTCXX = $(LLVM_PREFIX)clang++$(LLVM_SUFFIX)
else
-HOSTCC = gcc
-HOSTCXX = g++
+ifneq ($(filter %/,$(GCC)),)
+GCC_PREFIX := $(GCC)
+else ifneq ($(filter -%,$(GCC)),)
+GCC_SUFFIX := $(GCC)
+endif
+
+HOSTCC = $(GCC_PREFIX)gcc$(GCC_SUFFIX)
+HOSTCXX = $(GCC_PREFIX)g++$(GCC_SUFFIX)
endif
HOSTPKG_CONFIG = pkg-config

@@ -461,7 +467,7 @@ OBJDUMP = $(LLVM_PREFIX)llvm-objdump$(LLVM_SUFFIX)
READELF = $(LLVM_PREFIX)llvm-readelf$(LLVM_SUFFIX)
STRIP = $(LLVM_PREFIX)llvm-strip$(LLVM_SUFFIX)
else
-CC = $(CROSS_COMPILE)gcc
+CC = $(GCC_PREFIX)$(CROSS_COMPILE)gcc$(GCC_SUFFIX)
LD = $(CROSS_COMPILE)ld
AR = $(CROSS_COMPILE)ar
NM = $(CROSS_COMPILE)nm
diff --git a/tools/testing/selftests/lib.mk b/tools/testing/selftests/lib.mk
index 1a5cc3cd97ec..777757d54f42 100644
--- a/tools/testing/selftests/lib.mk
+++ b/tools/testing/selftests/lib.mk
@@ -30,7 +30,7 @@ endif # CROSS_COMPILE

CC := $(LLVM_PREFIX)clang$(LLVM_SUFFIX) $(CLANG_FLAGS) -fintegrated-as
else
-CC := $(CROSS_COMPILE)gcc
+CC := $(GCC_PREFIX)$(CROSS_COMPILE)gcc$(GCC_SUFFIX)
endif # LLVM

ifeq (0,$(MAKELEVEL))
--
2.34.1

2022-07-22 04:48:40

by Masahiro Yamada

Subject: Re: [PATCH] kbuild: introduce $(GCC) variable for path-prefix or version-suffix

On Wed, Jul 20, 2022 at 9:41 PM Dimitri John Ledkov
<[email protected]> wrote:
>
> Introduce $(GCC) variable with similar semantics to $(LLVM) for
> setting path-prefix or version-suffix.
>
> Currently to correctly and consistently use gcc-10 on Ubuntu 20.04
> LTS, to cross compile a kernel one has to do:
>
> $ make ... CROSS_COMPILE=riscv64-linux-gnu- \
> CC=riscv64-linux-gnu-gcc-10 \
> HOSTCC=gcc-10 \
> HOSTCXX=g++-10


I think this way is enough.




> With this change
>
> $ make ... CROSS_COMPILE=riscv64-linux-gnu- GCC=-10
>
> is sufficient to correctly select a consistent CC/HOSTCC/HOSTCXX set.


LLVM=-13 is useful to switch all tools in the LLVM suite
such as clang-13, ld.lld-13, llvm-ar-13, etc.



When you use GCC, the other tools come from binutils.

Also, I tend to think CC and HOSTCC/HOSTCXX are different groups.
There is no strong reason for the target GCC and the host GCC
must be the same version.

You can set CC, HOSTCC, HOSTCXX indivudually.


>
> Similarly GCC=/path/to/unpacked/toolchains/ can be used to select
> toolchain outside of PATH.

I think CROSS_COMPILE=/path/to/unpacked/toolchains/ is more common
because gcc and binutils are usually bundled together.




Overall, I do not think GCC= is so useful.
(at least not so useful as LLVM= syntax)





>
> Update documentation for LLVM variable, and mention that GCC variable
> can be used in a similar fashion to set path-prefix, or
> version-suffix.
>
> Signed-off-by: Dimitri John Ledkov <[email protected]>
> ---
> Documentation/kbuild/kbuild.rst | 12 ++++++++++--
> Makefile | 12 +++++++++---
> tools/testing/selftests/lib.mk | 2 +-
> 3 files changed, 20 insertions(+), 6 deletions(-)
>
> diff --git a/Documentation/kbuild/kbuild.rst b/Documentation/kbuild/kbuild.rst
> index ef19b9c13523..6382b082018e 100644
> --- a/Documentation/kbuild/kbuild.rst
> +++ b/Documentation/kbuild/kbuild.rst
> @@ -276,5 +276,13 @@ whoami and host, respectively.
>
> LLVM
> ----
> -If this variable is set to 1, Kbuild will use Clang and LLVM utilities instead
> -of GCC and GNU binutils to build the kernel.
> +If this variable is set to 1, Kbuild will use Clang and LLVM utilities
> +instead of GCC and GNU binutils to build the kernel. It can also be
> +used to set a path prefix, or a version suffix, see "Building
> +Linux with Clang/LLVM".
> +
> +GCC
> +---
> +This variable can be used similar to LLVM variable above to set a path
> +prefix, or a version suffix for GNU Toolchain binaries. See examples
> +in "Building Linux with Clang/LLVM".
> diff --git a/Makefile b/Makefile
> index 00fd80c5dd6e..e7bd0b572b14 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -433,8 +433,14 @@ endif
> HOSTCC = $(LLVM_PREFIX)clang$(LLVM_SUFFIX)
> HOSTCXX = $(LLVM_PREFIX)clang++$(LLVM_SUFFIX)
> else
> -HOSTCC = gcc
> -HOSTCXX = g++
> +ifneq ($(filter %/,$(GCC)),)
> +GCC_PREFIX := $(GCC)
> +else ifneq ($(filter -%,$(GCC)),)
> +GCC_SUFFIX := $(GCC)
> +endif
> +
> +HOSTCC = $(GCC_PREFIX)gcc$(GCC_SUFFIX)
> +HOSTCXX = $(GCC_PREFIX)g++$(GCC_SUFFIX)
> endif
> HOSTPKG_CONFIG = pkg-config
>
> @@ -461,7 +467,7 @@ OBJDUMP = $(LLVM_PREFIX)llvm-objdump$(LLVM_SUFFIX)
> READELF = $(LLVM_PREFIX)llvm-readelf$(LLVM_SUFFIX)
> STRIP = $(LLVM_PREFIX)llvm-strip$(LLVM_SUFFIX)
> else
> -CC = $(CROSS_COMPILE)gcc
> +CC = $(GCC_PREFIX)$(CROSS_COMPILE)gcc$(GCC_SUFFIX)
> LD = $(CROSS_COMPILE)ld
> AR = $(CROSS_COMPILE)ar
> NM = $(CROSS_COMPILE)nm
> diff --git a/tools/testing/selftests/lib.mk b/tools/testing/selftests/lib.mk
> index 1a5cc3cd97ec..777757d54f42 100644
> --- a/tools/testing/selftests/lib.mk
> +++ b/tools/testing/selftests/lib.mk
> @@ -30,7 +30,7 @@ endif # CROSS_COMPILE
>
> CC := $(LLVM_PREFIX)clang$(LLVM_SUFFIX) $(CLANG_FLAGS) -fintegrated-as
> else
> -CC := $(CROSS_COMPILE)gcc
> +CC := $(GCC_PREFIX)$(CROSS_COMPILE)gcc$(GCC_SUFFIX)
> endif # LLVM
>
> ifeq (0,$(MAKELEVEL))
> --
> 2.34.1
>


--
Best Regards

Masahiro Yamada