kbuild: dummy-tools: pretend we understand -fpatchable-function-entry

Commit 0f71dcfb4aef ("powerpc/ftrace: Add support for
-fpatchable-function-entry") added a script to check for
-fpatchable-function-entry compiler support. The script expects compiler
to emit the section __patchable_function_entries and few nops after a
function entry.

If the compiler understands and emits the above,
CONFIG_ARCH_USING_PATCHABLE_FUNCTION_ENTRY is set.

So teach dummy-tools' gcc about this.

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

kbuild: dummy-tools: make MPROFILE_KERNEL checks work on BE

Commit 2eab791f940b ("kbuild: dummy-tools: support MPROFILE_KERNEL
checks for ppc") added support for ppc64le's checks for
-mprofile-kernel.

Now, commit aec0ba7472a7 ("powerpc/64: Use -mprofile-kernel for big
endian ELFv2 kernels") added support for -mprofile-kernel even on
big-endian ppc.

So lift the check in gcc-check-mprofile-kernel.sh to support big-endian too.

Fixes: aec0ba7472a7 ("powerpc/64: Use -mprofile-kernel for big endian ELFv2 kernels")
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

kbuild: dummy-tools: pretend we understand __LONG_DOUBLE_128__

There is a test in powerpc's Kconfig which checks __LONG_DOUBLE_128__
and sets CONFIG_PPC_LONG_DOUBLE_128 if it is understood by the compiler.

We currently don't handle it, so this results in PPC_LONG_DOUBLE_128 not
being in super-config generated by dummy-tools. So take this into
account in the gcc script and preprocess __LONG_DOUBLE_128__ as "1".

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

kbuild: dummy-tools: avoid tmpdir leak in dummy gcc

When passed -print-file-name=plugin, the dummy gcc script creates a
temporary directory that is never cleaned up. To avoid cluttering
$TMPDIR, instead use a static directory included in the source tree.

Fixes: 76426e238834 ("kbuild: add dummy toolchains to enable all cc-option etc. in Kconfig")
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

kbuild: dummy-tools: adjust to stricter stackprotector check

Commit 3fb0fdb3bbe7 ("x86/stackprotector/32: Make the canary into a regular
percpu variable") modified the stackprotector check on 32-bit x86 to check
if gcc supports using %fs as canary. Adjust dummy-tools gcc script to pass
this new test by returning "%fs" rather than "%gs" if it detects
-mstack-protector-guard-reg=fs on command line.

Fixes: 3fb0fdb3bbe7 ("x86/stackprotector/32: Make the canary into a regular percpu variable")
Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

kbuild: check the minimum assembler version in Kconfig

Documentation/process/changes.rst defines the minimum assembler version
(binutils version), but we have never checked it in the build time.

Kbuild never invokes 'as' directly because all assembly files in the
kernel tree are *.S, hence must be preprocessed. I do not expect
raw assembly source files (*.s) would be added to the kernel tree.

Therefore, we always use $(CC) as the assembler driver, and commit
aa824e0c962b ("kbuild: remove AS variable") removed 'AS'. However,
we are still interested in the version of the assembler acting behind.

As usual, the --version option prints the version string.

$ as --version | head -n 1
GNU assembler (GNU Binutils for Ubuntu) 2.35.1

But, we do not have $(AS). So, we can add the -Wa prefix so that
$(CC) passes --version down to the backing assembler.

$ gcc -Wa,--version | head -n 1
gcc: fatal error: no input files
compilation terminated.

OK, we need to input something to satisfy gcc.

$ gcc -Wa,--version -c -x assembler /dev/null -o /dev/null | head -n 1
GNU assembler (GNU Binutils for Ubuntu) 2.35.1

The combination of Clang and GNU assembler works in the same way:

$ clang -no-integrated-as -Wa,--version -c -x assembler /dev/null -o /dev/null | head -n 1
GNU assembler (GNU Binutils for Ubuntu) 2.35.1

Clang with the integrated assembler fails like this:

$ clang -integrated-as -Wa,--version -c -x assembler /dev/null -o /dev/null | head -n 1
clang: error: unsupported argument '--version' to option 'Wa,'

For the last case, checking the error message is fragile. If the
proposal for -Wa,--version support [1] is accepted, this may not be
even an error in the future.

One easy way is to check if -integrated-as is present in the passed
arguments. We did not pass -integrated-as to CLANG_FLAGS before, but
we can make it explicit.

Nathan pointed out -integrated-as is the default for all of the
architectures/targets that the kernel cares about, but it goes
along with "explicit is better than implicit" policy. [2]

With all this in my mind, I implemented scripts/as-version.sh to
check the assembler version in Kconfig time.

$ scripts/as-version.sh gcc
GNU 23501
$ scripts/as-version.sh clang -no-integrated-as
GNU 23501
$ scripts/as-version.sh clang -integrated-as
LLVM 0

[1]: https://github.com/ClangBuiltLinux/linux/issues/1320
[2]: https://lore.kernel.org/linux-kbuild/20210307044253.v3h47ucq6ng25iay@archlinux-ax161/

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>

kbuild: dummy-tools: adjust to scripts/cc-version.sh

Commit aec6c60a01d3 ("kbuild: check the minimum compiler version in
Kconfig") changed how the script detects the compiler version.

Get 'make CROSS_COMPILE=scripts/dummy-tools/' back working again.

Fixes: aec6c60a01d3 ("kbuild: check the minimum compiler version in Kconfig")
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Acked-by: Miguel Ojeda <ojeda@kernel.org>

kbuild: dummy-tools: support MPROFILE_KERNEL checks for ppc

ppc64le checks for -mprofile-kernel to define MPROFILE_KERNEL Kconfig.
Kconfig calls arch/powerpc/tools/gcc-check-mprofile-kernel.sh for that
purpose. This script performs two checks:
1) build with -mprofile-kernel should contain "_mcount"
2) build with -mprofile-kernel with a function marked as "notrace"
should not produce "_mcount"

So support this in dummy-tools' gcc, so that we have MPROFILE_KERNEL
always true.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

kbuild: dummy-tools: fix inverted tests for gcc

There is a test in Kconfig which takes inverted value of a compiler
check:
* config CC_HAS_INT128
def_bool !$(cc-option,$(m64-flag) -D__SIZEOF_INT128__=0)

This results in CC_HAS_INT128 not being in super-config generated by
dummy-tools. So take this into account in the gcc script.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

kbuild: simplify GCC_PLUGINS enablement in dummy-tools/gcc

With commit 1e860048c53e ("gcc-plugins: simplify GCC plugin-dev
capability test") applied, this hunk can be way simplified because
now scripts/gcc-plugins/Kconfig only checks plugin-version.h

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

kbuild: add dummy toolchains to enable all cc-option etc. in Kconfig

Staring v4.18, Kconfig evaluates compiler capabilities, and hides CONFIG
options your compiler does not support. This works well if you configure
and build the kernel on the same host machine.

It is inconvenient if you prepare the .config that is carried to a
different build environment (typically this happens when you package
the kernel for distros) because using a different compiler potentially
produces different CONFIG options than the real build environment.
So, you probably want to make as many options visible as possible.
In other words, you need to create a super-set of CONFIG options that
cover any build environment. If some of the CONFIG options turned out
to be unsupported on the build machine, they are automatically disabled
by the nature of Kconfig.

However, it is not feasible to get a full-featured compiler for every
arch.

This issue was discussed here:

https://lkml.org/lkml/2019/12/9/620

Other than distros, savedefconfig is also a problem. Some arch sub-systems
periodically resync defconfig files. If you use a less-capable compiler
for savedefconfig, options that do not meet 'depends on $(cc-option,...)'
will be forcibly disabled. So, 'make defconfig && make savedefconfig'
may silently change the behavior.

This commit adds a set of dummy toolchains that pretend to support any
feature.

Most of compiler features are tested by cc-option, which simply checks
the exit code of $(CC). The dummy tools are shell scripts that always
exit with 0. So, $(cc-option, ...) is evaluated as 'y'.

There are more complicated checks such as:

scripts/gcc-x86_{32,64}-has-stack-protector.sh
scripts/gcc-plugin.sh
scripts/tools-support-relr.sh

scripts/dummy-tools/gcc passes all checks.

From the top directory of the source tree, you can do:

$ make CROSS_COMPILE=scripts/dummy-tools/ oldconfig

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Philipp Rudo <prudo@linux.ibm.com>
Tested-by: Jeremy Cline <jcline@redhat.com>