We get constant feedback that the command line invocation of make is too
long. CROSS_COMPILE is helpful when a toolchain has a prefix of the
target triple, or is an absolute path outside of $PATH, but it's mostly
redundant for a given ARCH.
Instead, let's infer --target from SRCARCH, and move some flag handling into a
new file included from the top level Makefile.
Changes v5 -> v6:
* Use indirection as per Linus.
* Change hexagon triple to use -musl rather than -gnu. glibc doesn't
have support for hexagon, and hexagon-linux-musl is the triple we use
in CI.
https://github.com/ClangBuiltLinux/continuous-integration2/blob/d659897d1700894d67feb64fe28e298da399a287/generator.yml#L53
* Pick up Fangrui's RB.
* Reorder use of Env vars in documentation to use command line
parameters instead, for consistency.
Changes v4 -> v5:
* Include previously missing first patch!
Changes v3 -> v4:
* Remove the requirement that LLVM_IAS=1 be set, as per Masahiro.
* Remove the Documentation/ change from patch 2, as per Masahiro and
Nathan.
* Add Documentation/ change as patch 3, from Masahiro.
* Reword commit message of patch 2, as per Nathan.
* Change patch 2 oneline to refer to --target and CC=clang (not
CROSS_COMPILE).
* Carry Arnd's and Nathan's AB/RB/TB tags, confirmed ok on IRC+discord.
Changes v2 -> v3:
* Remove requirement that LLVM=1 be set. Instead, if building with just
CC=clang LLVM_IAS=1 instead of LLVM=1 LLVM_IAS=1, you should use
LD=ld.lld explicitly, or LD=aarch64-linux-gnu-ld. (As per Masahiro)
Example:
$ ARCH=arm64 make CC=clang LLVM_IAS=1 LD=ld.lld OBJCOPY=llvm-objcopy \
STRIP=llvm-strip -j72 defconfig all
(It's still preferable to use LLVM=1 IMO, but this is maximally
flexible.)
* Change oneliner from LLVM=1 to CC=clang.
* Update Docs slightly.
Changes v1 -> v2:
* patch 1/2 untouched.
* Fix typos in commit message as per Geert and Masahiro.
* Use SRCARCH instead of ARCH, simplifying x86 handling, as per
Masahiro. Add his sugguested by tag.
* change commit oneline from 'drop' to 'infer.'
* Add detail about explicit host --target and relationship of ARCH to
SRCARCH, as per Masahiro.
Nick Desaulniers (3):
Makefile: move initial clang flag handling into scripts/Makefile.clang
Makefile: infer --target from ARCH for CC=clang
Documentation/llvm: update CROSS_COMPILE inferencing
Documentation/kbuild/llvm.rst | 19 ++++++++++++++++++-
MAINTAINERS | 1 +
Makefile | 15 +--------------
scripts/Makefile.clang | 35 +++++++++++++++++++++++++++++++++++
4 files changed, 55 insertions(+), 15 deletions(-)
create mode 100644 scripts/Makefile.clang
base-commit: d7a86429dbc691bf540688fcc8542cc20246a85b
--
2.32.0.554.ge1b32706d8-goog
With some of the changes we'd like to make to CROSS_COMPILE, the initial
block of clang flag handling which controls things like the target triple,
whether or not to use the integrated assembler and how to find GAS,
and erroring on unknown warnings is becoming unwieldy. Move it into its
own file under scripts/.
Reviewed-by: Nathan Chancellor <[email protected]>
Signed-off-by: Nick Desaulniers <[email protected]>
---
MAINTAINERS | 1 +
Makefile | 15 +--------------
scripts/Makefile.clang | 14 ++++++++++++++
3 files changed, 16 insertions(+), 14 deletions(-)
create mode 100644 scripts/Makefile.clang
diff --git a/MAINTAINERS b/MAINTAINERS
index 19135a9d778e..3af8d39f43ef 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4501,6 +4501,7 @@ B: https://github.com/ClangBuiltLinux/linux/issues
C: irc://chat.freenode.net/clangbuiltlinux
F: Documentation/kbuild/llvm.rst
F: include/linux/compiler-clang.h
+F: scripts/Makefile.clang
F: scripts/clang-tools/
K: \b(?i:clang|llvm)\b
diff --git a/Makefile b/Makefile
index 6b555f64df06..444558e62cbc 100644
--- a/Makefile
+++ b/Makefile
@@ -586,20 +586,7 @@ endif
CC_VERSION_TEXT = $(subst $(pound),,$(shell $(CC) --version 2>/dev/null | head -n 1))
ifneq ($(findstring clang,$(CC_VERSION_TEXT)),)
-ifneq ($(CROSS_COMPILE),)
-CLANG_FLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%))
-endif
-ifeq ($(LLVM_IAS),1)
-CLANG_FLAGS += -integrated-as
-else
-CLANG_FLAGS += -no-integrated-as
-GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)elfedit))
-CLANG_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))
-endif
-CLANG_FLAGS += -Werror=unknown-warning-option
-KBUILD_CFLAGS += $(CLANG_FLAGS)
-KBUILD_AFLAGS += $(CLANG_FLAGS)
-export CLANG_FLAGS
+include $(srctree)/scripts/Makefile.clang
endif
# Include this also for config targets because some architectures need
diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang
new file mode 100644
index 000000000000..297932e973d4
--- /dev/null
+++ b/scripts/Makefile.clang
@@ -0,0 +1,14 @@
+ifneq ($(CROSS_COMPILE),)
+CLANG_FLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%))
+endif
+ifeq ($(LLVM_IAS),1)
+CLANG_FLAGS += -integrated-as
+else
+CLANG_FLAGS += -no-integrated-as
+GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)elfedit))
+CLANG_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))
+endif
+CLANG_FLAGS += -Werror=unknown-warning-option
+KBUILD_CFLAGS += $(CLANG_FLAGS)
+KBUILD_AFLAGS += $(CLANG_FLAGS)
+export CLANG_FLAGS
--
2.32.0.554.ge1b32706d8-goog
As noted by Masahiro, document how we can generally infer CROSS_COMPILE
(and the more specific details about --target and --prefix) based on
ARCH.
Change use of env vars to command line parameters.
Suggested-by: Masahiro Yamada <[email protected]>
Reviewed-by: Fangrui Song <[email protected]>
Signed-off-by: Nick Desaulniers <[email protected]>
---
Changes v5 -> v6:
* Pick up Fangrui's RB tag.
* Change use of env vars to command line parameters for consistency.
Documentation/kbuild/llvm.rst | 19 ++++++++++++++++++-
1 file changed, 18 insertions(+), 1 deletion(-)
diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst
index b18401d2ba82..f8a360958f4c 100644
--- a/Documentation/kbuild/llvm.rst
+++ b/Documentation/kbuild/llvm.rst
@@ -38,7 +38,7 @@ Cross Compiling
A single Clang compiler binary will typically contain all supported backends,
which can help simplify cross compiling. ::
- ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make CC=clang
+ make ARCH=arm64 CC=clang CROSS_COMPILE=aarch64-linux-gnu-
``CROSS_COMPILE`` is not used to prefix the Clang compiler binary, instead
``CROSS_COMPILE`` is used to set a command line flag: ``--target=<triple>``. For
@@ -63,6 +63,23 @@ They can be enabled individually. The full list of the parameters: ::
Currently, the integrated assembler is disabled by default. You can pass
``LLVM_IAS=1`` to enable it.
+Omitting CROSS_COMPILE
+----------------------
+
+As explained above, ``CROSS_COMPILE`` is used to set ``--target=<triple>``.
+
+Unless ``LLVM_IAS=1`` is specified, ``CROSS_COMPILE`` is also used to derive
+``--prefix=<path>`` to search for the GNU assembler and linker.
+
+If ``CROSS_COMPILE`` is not specified, the ``--target=<triple>`` is inferred
+from ``ARCH``.
+
+That means if you use only LLVM tools, ``CROSS_COMPILE`` becomes unnecessary.
+
+For example, to cross-compile the arm64 kernel::
+
+ make ARCH=arm64 LLVM=1 LLVM_IAS=1
+
Supported Architectures
-----------------------
--
2.32.0.554.ge1b32706d8-goog
On 8/2/2021 11:39 AM, 'Nick Desaulniers' via Clang Built Linux wrote:
> As noted by Masahiro, document how we can generally infer CROSS_COMPILE
> (and the more specific details about --target and --prefix) based on
> ARCH.
>
> Change use of env vars to command line parameters.
>
> Suggested-by: Masahiro Yamada <[email protected]>
> Reviewed-by: Fangrui Song <[email protected]>
> Signed-off-by: Nick Desaulniers <[email protected]>
Thanks for the update, I think this is much easier for non-CBL folks to
understand.
Reviewed-by: Nathan Chancellor <[email protected]>
> ---
> Changes v5 -> v6:
> * Pick up Fangrui's RB tag.
> * Change use of env vars to command line parameters for consistency.
>
> Documentation/kbuild/llvm.rst | 19 ++++++++++++++++++-
> 1 file changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst
> index b18401d2ba82..f8a360958f4c 100644
> --- a/Documentation/kbuild/llvm.rst
> +++ b/Documentation/kbuild/llvm.rst
> @@ -38,7 +38,7 @@ Cross Compiling
> A single Clang compiler binary will typically contain all supported backends,
> which can help simplify cross compiling. ::
>
> - ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make CC=clang
> + make ARCH=arm64 CC=clang CROSS_COMPILE=aarch64-linux-gnu-
>
> ``CROSS_COMPILE`` is not used to prefix the Clang compiler binary, instead
> ``CROSS_COMPILE`` is used to set a command line flag: ``--target=<triple>``. For
> @@ -63,6 +63,23 @@ They can be enabled individually. The full list of the parameters: ::
> Currently, the integrated assembler is disabled by default. You can pass
> ``LLVM_IAS=1`` to enable it.
>
> +Omitting CROSS_COMPILE
> +----------------------
> +
> +As explained above, ``CROSS_COMPILE`` is used to set ``--target=<triple>``.
> +
> +Unless ``LLVM_IAS=1`` is specified, ``CROSS_COMPILE`` is also used to derive
> +``--prefix=<path>`` to search for the GNU assembler and linker.
> +
> +If ``CROSS_COMPILE`` is not specified, the ``--target=<triple>`` is inferred
> +from ``ARCH``.
> +
> +That means if you use only LLVM tools, ``CROSS_COMPILE`` becomes unnecessary.
> +
> +For example, to cross-compile the arm64 kernel::
> +
> + make ARCH=arm64 LLVM=1 LLVM_IAS=1
> +
> Supported Architectures
> -----------------------
>
>
On Mon, Aug 2, 2021 at 11:39 AM Nick Desaulniers
<[email protected]> wrote:
>
> With some of the changes we'd like to make to CROSS_COMPILE, the initial
> block of clang flag handling which controls things like the target triple,
> whether or not to use the integrated assembler and how to find GAS,
> and erroring on unknown warnings is becoming unwieldy. Move it into its
> own file under scripts/.
>
> Reviewed-by: Nathan Chancellor <[email protected]>
> Signed-off-by: Nick Desaulniers <[email protected]>
> ---
> MAINTAINERS | 1 +
> Makefile | 15 +--------------
> scripts/Makefile.clang | 14 ++++++++++++++
> 3 files changed, 16 insertions(+), 14 deletions(-)
> create mode 100644 scripts/Makefile.clang
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 19135a9d778e..3af8d39f43ef 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -4501,6 +4501,7 @@ B: https://github.com/ClangBuiltLinux/linux/issues
> C: irc://chat.freenode.net/clangbuiltlinux
> F: Documentation/kbuild/llvm.rst
> F: include/linux/compiler-clang.h
> +F: scripts/Makefile.clang
> F: scripts/clang-tools/
> K: \b(?i:clang|llvm)\b
>
> diff --git a/Makefile b/Makefile
> index 6b555f64df06..444558e62cbc 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -586,20 +586,7 @@ endif
> CC_VERSION_TEXT = $(subst $(pound),,$(shell $(CC) --version 2>/dev/null | head -n 1))
>
> ifneq ($(findstring clang,$(CC_VERSION_TEXT)),)
> -ifneq ($(CROSS_COMPILE),)
> -CLANG_FLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%))
> -endif
> -ifeq ($(LLVM_IAS),1)
> -CLANG_FLAGS += -integrated-as
> -else
> -CLANG_FLAGS += -no-integrated-as
> -GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)elfedit))
> -CLANG_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))
> -endif
> -CLANG_FLAGS += -Werror=unknown-warning-option
> -KBUILD_CFLAGS += $(CLANG_FLAGS)
> -KBUILD_AFLAGS += $(CLANG_FLAGS)
> -export CLANG_FLAGS
> +include $(srctree)/scripts/Makefile.clang
> endif
>
> # Include this also for config targets because some architectures need
> diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang
> new file mode 100644
> index 000000000000..297932e973d4
> --- /dev/null
> +++ b/scripts/Makefile.clang
> @@ -0,0 +1,14 @@
> +ifneq ($(CROSS_COMPILE),)
> +CLANG_FLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%))
> +endif
> +ifeq ($(LLVM_IAS),1)
> +CLANG_FLAGS += -integrated-as
-i* options are for includes. -fintegrated-as is the canonical spelling.
Since -fintegrated-as is the default (for most llvm/lib/Target/
targets and the ones clang builds actually support),
it can even be deleted.
> +else
> +CLANG_FLAGS += -no-integrated-as
> +GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)elfedit))
> +CLANG_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))
> +endif
> +CLANG_FLAGS += -Werror=unknown-warning-option
> +KBUILD_CFLAGS += $(CLANG_FLAGS)
> +KBUILD_AFLAGS += $(CLANG_FLAGS)
> +export CLANG_FLAGS
> --
> 2.32.0.554.ge1b32706d8-goog
>
On Mon, Aug 2, 2021 at 2:06 PM Fāng-ruì Sòng <[email protected]> wrote:
>
> On Mon, Aug 2, 2021 at 11:39 AM Nick Desaulniers
> <[email protected]> wrote:
> > diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang
> > new file mode 100644
> > index 000000000000..297932e973d4
> > --- /dev/null
> > +++ b/scripts/Makefile.clang
> > @@ -0,0 +1,14 @@
> > +ifneq ($(CROSS_COMPILE),)
> > +CLANG_FLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%))
> > +endif
> > +ifeq ($(LLVM_IAS),1)
> > +CLANG_FLAGS += -integrated-as
>
> -i* options are for includes. -fintegrated-as is the canonical spelling.
> Since -fintegrated-as is the default (for most llvm/lib/Target/
> targets and the ones clang builds actually support),
> it can even be deleted.
It was made explicit by Masahiro in
git.kernel.org/linus/ba64beb17493a4bfec563100c86a462a15926f24
So I don't think we need to go back to the implicit default.
It's definitely nicer to use groupings rather than these raw prefixed
flags IMO. If you sent a patch for that I would approve of it.
Otherwise we don't really need to change this as this is how it's
worked in LLVM for as long as we've been able to build the kernel with
LLVM.
--
Thanks,
~Nick Desaulniers
On Tue, Aug 3, 2021 at 3:39 AM 'Nick Desaulniers' via Clang Built
Linux <[email protected]> wrote:
>
> As noted by Masahiro, document how we can generally infer CROSS_COMPILE
> (and the more specific details about --target and --prefix) based on
> ARCH.
>
> Change use of env vars to command line parameters.
>
> Suggested-by: Masahiro Yamada <[email protected]>
> Reviewed-by: Fangrui Song <[email protected]>
> Signed-off-by: Nick Desaulniers <[email protected]>
> ---
> Changes v5 -> v6:
> * Pick up Fangrui's RB tag.
> * Change use of env vars to command line parameters for consistency.
>
> Documentation/kbuild/llvm.rst | 19 ++++++++++++++++++-
> 1 file changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst
> index b18401d2ba82..f8a360958f4c 100644
> --- a/Documentation/kbuild/llvm.rst
> +++ b/Documentation/kbuild/llvm.rst
> @@ -38,7 +38,7 @@ Cross Compiling
> A single Clang compiler binary will typically contain all supported backends,
> which can help simplify cross compiling. ::
>
> - ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make CC=clang
> + make ARCH=arm64 CC=clang CROSS_COMPILE=aarch64-linux-gnu-
>
> ``CROSS_COMPILE`` is not used to prefix the Clang compiler binary, instead
> ``CROSS_COMPILE`` is used to set a command line flag: ``--target=<triple>``. For
> @@ -63,6 +63,23 @@ They can be enabled individually. The full list of the parameters: ::
> Currently, the integrated assembler is disabled by default. You can pass
> ``LLVM_IAS=1`` to enable it.
>
> +Omitting CROSS_COMPILE
> +----------------------
> +
> +As explained above, ``CROSS_COMPILE`` is used to set ``--target=<triple>``.
> +
> +Unless ``LLVM_IAS=1`` is specified, ``CROSS_COMPILE`` is also used to derive
> +``--prefix=<path>`` to search for the GNU assembler and linker.
Is there any place where we rely on --prefix
to search for the linker?
In general, the compiler stops after generating an object
since it is passed with the -c option.
The linking stage is separated.
In the old days, VDSO was an exceptional case
where $(CC) was used as the linker driver, but
commit fe00e50b2db8c60e4ec90befad1f5bab8ca2c800 fixed it.
> +
> +If ``CROSS_COMPILE`` is not specified, the ``--target=<triple>`` is inferred
> +from ``ARCH``.
> +
> +That means if you use only LLVM tools, ``CROSS_COMPILE`` becomes unnecessary.
> +
> +For example, to cross-compile the arm64 kernel::
> +
> + make ARCH=arm64 LLVM=1 LLVM_IAS=1
> +
> Supported Architectures
> -----------------------
>
> --
> 2.32.0.554.ge1b32706d8-goog
>
> --
> You received this message because you are subscribed to the Google Groups "Clang Built Linux" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to [email protected].
> To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/20210802183910.1802120-4-ndesaulniers%40google.com.
--
Best Regards
Masahiro Yamada
On Tue, Aug 3, 2021 at 6:06 AM 'Fāng-ruì Sòng' via Clang Built Linux
<[email protected]> wrote:
>
> On Mon, Aug 2, 2021 at 11:39 AM Nick Desaulniers
> <[email protected]> wrote:
> >
> > With some of the changes we'd like to make to CROSS_COMPILE, the initial
> > block of clang flag handling which controls things like the target triple,
> > whether or not to use the integrated assembler and how to find GAS,
> > and erroring on unknown warnings is becoming unwieldy. Move it into its
> > own file under scripts/.
> >
> > Reviewed-by: Nathan Chancellor <[email protected]>
> > Signed-off-by: Nick Desaulniers <[email protected]>
> > ---
> > MAINTAINERS | 1 +
> > Makefile | 15 +--------------
> > scripts/Makefile.clang | 14 ++++++++++++++
> > 3 files changed, 16 insertions(+), 14 deletions(-)
> > create mode 100644 scripts/Makefile.clang
> >
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index 19135a9d778e..3af8d39f43ef 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -4501,6 +4501,7 @@ B: https://github.com/ClangBuiltLinux/linux/issues
> > C: irc://chat.freenode.net/clangbuiltlinux
> > F: Documentation/kbuild/llvm.rst
> > F: include/linux/compiler-clang.h
> > +F: scripts/Makefile.clang
> > F: scripts/clang-tools/
> > K: \b(?i:clang|llvm)\b
> >
> > diff --git a/Makefile b/Makefile
> > index 6b555f64df06..444558e62cbc 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -586,20 +586,7 @@ endif
> > CC_VERSION_TEXT = $(subst $(pound),,$(shell $(CC) --version 2>/dev/null | head -n 1))
> >
> > ifneq ($(findstring clang,$(CC_VERSION_TEXT)),)
> > -ifneq ($(CROSS_COMPILE),)
> > -CLANG_FLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%))
> > -endif
> > -ifeq ($(LLVM_IAS),1)
> > -CLANG_FLAGS += -integrated-as
> > -else
> > -CLANG_FLAGS += -no-integrated-as
> > -GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)elfedit))
> > -CLANG_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))
> > -endif
> > -CLANG_FLAGS += -Werror=unknown-warning-option
> > -KBUILD_CFLAGS += $(CLANG_FLAGS)
> > -KBUILD_AFLAGS += $(CLANG_FLAGS)
> > -export CLANG_FLAGS
> > +include $(srctree)/scripts/Makefile.clang
> > endif
> >
> > # Include this also for config targets because some architectures need
> > diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang
> > new file mode 100644
> > index 000000000000..297932e973d4
> > --- /dev/null
> > +++ b/scripts/Makefile.clang
> > @@ -0,0 +1,14 @@
> > +ifneq ($(CROSS_COMPILE),)
> > +CLANG_FLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%))
> > +endif
> > +ifeq ($(LLVM_IAS),1)
> > +CLANG_FLAGS += -integrated-as
>
> -i* options are for includes. -fintegrated-as is the canonical spelling.
If -fintegrated-as is preferred to -integrated-as,
please send a patch.
(on top of this series)
Thanks.
> Since -fintegrated-as is the default (for most llvm/lib/Target/
> targets and the ones clang builds actually support),
> it can even be deleted.
>
> > +else
> > +CLANG_FLAGS += -no-integrated-as
> > +GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)elfedit))
> > +CLANG_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))
> > +endif
> > +CLANG_FLAGS += -Werror=unknown-warning-option
> > +KBUILD_CFLAGS += $(CLANG_FLAGS)
> > +KBUILD_AFLAGS += $(CLANG_FLAGS)
> > +export CLANG_FLAGS
> > --
> > 2.32.0.554.ge1b32706d8-goog
> >
>
> --
> You received this message because you are subscribed to the Google Groups "Clang Built Linux" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to [email protected].
> To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/CAFP8O3Jc%3DiwzAQojgBZZzdT8iVBY9TO6GLTq%2B0vkXoo6L5JJ-A%40mail.gmail.com.
--
Best Regards
Masahiro Yamada
On Thu, Aug 5, 2021 at 6:58 AM Masahiro Yamada <[email protected]> wrote:
>
> On Tue, Aug 3, 2021 at 3:39 AM 'Nick Desaulniers' via Clang Built
> Linux <[email protected]> wrote:
> > diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst
> > index b18401d2ba82..f8a360958f4c 100644
> > --- a/Documentation/kbuild/llvm.rst
> > +++ b/Documentation/kbuild/llvm.rst
> > @@ -63,6 +63,23 @@ They can be enabled individually. The full list of the parameters: ::
> > Currently, the integrated assembler is disabled by default. You can pass
> > ``LLVM_IAS=1`` to enable it.
> >
> > +Omitting CROSS_COMPILE
> > +----------------------
> > +
> > +As explained above, ``CROSS_COMPILE`` is used to set ``--target=<triple>``.
> > +
> > +Unless ``LLVM_IAS=1`` is specified, ``CROSS_COMPILE`` is also used to derive
> > +``--prefix=<path>`` to search for the GNU assembler and linker.
>
>
> Is there any place where we rely on --prefix
> to search for the linker?
>
> In general, the compiler stops after generating an object
> since it is passed with the -c option.
> The linking stage is separated.
>
> In the old days, VDSO was an exceptional case
> where $(CC) was used as the linker driver, but
> commit fe00e50b2db8c60e4ec90befad1f5bab8ca2c800 fixed it.
See my previous reply to Fangrui.
https://lore.kernel.org/lkml/CAKwvOdnK=SUm1_--tcLRO3LVeXd_2Srfv2tsZCUW0uXXa1W_pg@mail.gmail.com/
To be more specific, I believe this is still a problem for ppc vdso.
https://github.com/ClangBuiltLinux/linux/issues/774
I had sent patches for that, but binutils 2.26 would crash (IIUC,
newer GNU binutils are ok). See this thread:
https://lore.kernel.org/lkml/[email protected]/
So "we'd prefer the linker was used as the driver, but there's at
least one place I know of in the tree where that's not currently the
case."
--
Thanks,
~Nick Desaulniers
On Thu, Aug 5, 2021 at 11:27 AM Nick Desaulniers
<[email protected]> wrote:
>
> On Thu, Aug 5, 2021 at 6:58 AM Masahiro Yamada <[email protected]> wrote:
> >
> > On Tue, Aug 3, 2021 at 3:39 AM 'Nick Desaulniers' via Clang Built
> > Linux <[email protected]> wrote:
> > > diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst
> > > index b18401d2ba82..f8a360958f4c 100644
> > > --- a/Documentation/kbuild/llvm.rst
> > > +++ b/Documentation/kbuild/llvm.rst
> > > @@ -63,6 +63,23 @@ They can be enabled individually. The full list of the parameters: ::
> > > Currently, the integrated assembler is disabled by default. You can pass
> > > ``LLVM_IAS=1`` to enable it.
> > >
> > > +Omitting CROSS_COMPILE
> > > +----------------------
> > > +
> > > +As explained above, ``CROSS_COMPILE`` is used to set ``--target=<triple>``.
> > > +
> > > +Unless ``LLVM_IAS=1`` is specified, ``CROSS_COMPILE`` is also used to derive
> > > +``--prefix=<path>`` to search for the GNU assembler and linker.
> >
> >
> > Is there any place where we rely on --prefix
> > to search for the linker?
> >
> > In general, the compiler stops after generating an object
> > since it is passed with the -c option.
> > The linking stage is separated.
> >
> > In the old days, VDSO was an exceptional case
> > where $(CC) was used as the linker driver, but
> > commit fe00e50b2db8c60e4ec90befad1f5bab8ca2c800 fixed it.
>
> See my previous reply to Fangrui.
> https://lore.kernel.org/lkml/CAKwvOdnK=SUm1_--tcLRO3LVeXd_2Srfv2tsZCUW0uXXa1W_pg@mail.gmail.com/
>
> To be more specific, I believe this is still a problem for ppc vdso.
> https://github.com/ClangBuiltLinux/linux/issues/774
>
> I had sent patches for that, but binutils 2.26 would crash (IIUC,
> newer GNU binutils are ok). See this thread:
> https://lore.kernel.org/lkml/[email protected]/
>
> So "we'd prefer the linker was used as the driver, but there's at
> least one place I know of in the tree where that's not currently the
> case."
Also, I think the CC_CAN_LINK functionality also fits the bill.
https://github.com/ClangBuiltLinux/linux/issues/1290
--
Thanks,
~Nick Desaulniers
On Fri, Aug 6, 2021 at 3:29 AM Nick Desaulniers <[email protected]> wrote:
>
> On Thu, Aug 5, 2021 at 11:27 AM Nick Desaulniers
> <[email protected]> wrote:
> >
> > On Thu, Aug 5, 2021 at 6:58 AM Masahiro Yamada <[email protected]> wrote:
> > >
> > > On Tue, Aug 3, 2021 at 3:39 AM 'Nick Desaulniers' via Clang Built
> > > Linux <[email protected]> wrote:
> > > > diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst
> > > > index b18401d2ba82..f8a360958f4c 100644
> > > > --- a/Documentation/kbuild/llvm.rst
> > > > +++ b/Documentation/kbuild/llvm.rst
> > > > @@ -63,6 +63,23 @@ They can be enabled individually. The full list of the parameters: ::
> > > > Currently, the integrated assembler is disabled by default. You can pass
> > > > ``LLVM_IAS=1`` to enable it.
> > > >
> > > > +Omitting CROSS_COMPILE
> > > > +----------------------
> > > > +
> > > > +As explained above, ``CROSS_COMPILE`` is used to set ``--target=<triple>``.
> > > > +
> > > > +Unless ``LLVM_IAS=1`` is specified, ``CROSS_COMPILE`` is also used to derive
> > > > +``--prefix=<path>`` to search for the GNU assembler and linker.
> > >
> > >
> > > Is there any place where we rely on --prefix
> > > to search for the linker?
> > >
> > > In general, the compiler stops after generating an object
> > > since it is passed with the -c option.
> > > The linking stage is separated.
> > >
> > > In the old days, VDSO was an exceptional case
> > > where $(CC) was used as the linker driver, but
> > > commit fe00e50b2db8c60e4ec90befad1f5bab8ca2c800 fixed it.
> >
> > See my previous reply to Fangrui.
> > https://lore.kernel.org/lkml/CAKwvOdnK=SUm1_--tcLRO3LVeXd_2Srfv2tsZCUW0uXXa1W_pg@mail.gmail.com/
> >
> > To be more specific, I believe this is still a problem for ppc vdso.
> > https://github.com/ClangBuiltLinux/linux/issues/774
> >
> > I had sent patches for that, but binutils 2.26 would crash (IIUC,
> > newer GNU binutils are ok). See this thread:
> > https://lore.kernel.org/lkml/[email protected]/
> >
> > So "we'd prefer the linker was used as the driver, but there's at
> > least one place I know of in the tree where that's not currently the
> > case."
>
> Also, I think the CC_CAN_LINK functionality also fits the bill.
> https://github.com/ClangBuiltLinux/linux/issues/1290
> --
> Thanks,
> ~Nick Desaulniers
Ah, this is it.
Thanks.
--
Best Regards
Masahiro Yamada
On Tue, Aug 3, 2021 at 3:39 AM Nick Desaulniers <[email protected]> wrote:
>
> We get constant feedback that the command line invocation of make is too
> long. CROSS_COMPILE is helpful when a toolchain has a prefix of the
> target triple, or is an absolute path outside of $PATH, but it's mostly
> redundant for a given ARCH.
>
> Instead, let's infer --target from SRCARCH, and move some flag handling into a
> new file included from the top level Makefile.
Series, applied to linux-kbuild.
Thanks.
> Changes v5 -> v6:
> * Use indirection as per Linus.
> * Change hexagon triple to use -musl rather than -gnu. glibc doesn't
> have support for hexagon, and hexagon-linux-musl is the triple we use
> in CI.
> https://github.com/ClangBuiltLinux/continuous-integration2/blob/d659897d1700894d67feb64fe28e298da399a287/generator.yml#L53
> * Pick up Fangrui's RB.
> * Reorder use of Env vars in documentation to use command line
> parameters instead, for consistency.
>
> Changes v4 -> v5:
> * Include previously missing first patch!
>
> Changes v3 -> v4:
> * Remove the requirement that LLVM_IAS=1 be set, as per Masahiro.
> * Remove the Documentation/ change from patch 2, as per Masahiro and
> Nathan.
> * Add Documentation/ change as patch 3, from Masahiro.
> * Reword commit message of patch 2, as per Nathan.
> * Change patch 2 oneline to refer to --target and CC=clang (not
> CROSS_COMPILE).
> * Carry Arnd's and Nathan's AB/RB/TB tags, confirmed ok on IRC+discord.
>
> Changes v2 -> v3:
> * Remove requirement that LLVM=1 be set. Instead, if building with just
> CC=clang LLVM_IAS=1 instead of LLVM=1 LLVM_IAS=1, you should use
> LD=ld.lld explicitly, or LD=aarch64-linux-gnu-ld. (As per Masahiro)
> Example:
>
> $ ARCH=arm64 make CC=clang LLVM_IAS=1 LD=ld.lld OBJCOPY=llvm-objcopy \
> STRIP=llvm-strip -j72 defconfig all
>
> (It's still preferable to use LLVM=1 IMO, but this is maximally
> flexible.)
> * Change oneliner from LLVM=1 to CC=clang.
> * Update Docs slightly.
>
> Changes v1 -> v2:
> * patch 1/2 untouched.
> * Fix typos in commit message as per Geert and Masahiro.
> * Use SRCARCH instead of ARCH, simplifying x86 handling, as per
> Masahiro. Add his sugguested by tag.
> * change commit oneline from 'drop' to 'infer.'
> * Add detail about explicit host --target and relationship of ARCH to
> SRCARCH, as per Masahiro.
>
> Nick Desaulniers (3):
> Makefile: move initial clang flag handling into scripts/Makefile.clang
> Makefile: infer --target from ARCH for CC=clang
> Documentation/llvm: update CROSS_COMPILE inferencing
>
> Documentation/kbuild/llvm.rst | 19 ++++++++++++++++++-
> MAINTAINERS | 1 +
> Makefile | 15 +--------------
> scripts/Makefile.clang | 35 +++++++++++++++++++++++++++++++++++
> 4 files changed, 55 insertions(+), 15 deletions(-)
> create mode 100644 scripts/Makefile.clang
>
>
> base-commit: d7a86429dbc691bf540688fcc8542cc20246a85b
> --
> 2.32.0.554.ge1b32706d8-goog
>
--
Best Regards
Masahiro Yamada