[PATCH v6 05/11] init: add nolibc build support

[Thomas Weißschuh]

Building userspace applications through the kbuild "userprogs" framework
requires a libc. Kernel toolchains often do not contain a libc.
In this case it is useful to use the nolibc library from the kernel tree.
Nolibc does not support all architectures and requires compiler flags.

Add a kconfig option, so users can know where it is available and provide a
variable for common options.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@xxxxxxxxxxxxx>
Reviewed-by: Nicolas Schier <n.schier@xxxxxx>
---
 MAINTAINERS          |  2 ++
 init/Kconfig         |  2 ++
 init/Kconfig.nolibc  | 16 ++++++++++++++++
 init/Makefile.nolibc | 13 +++++++++++++
 4 files changed, 33 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 2fb1c75afd16..be4f6242b3fc 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -18960,6 +18960,8 @@ M:	Willy Tarreau <w@xxxxxx>
 M:	Thomas Weißschuh <linux@xxxxxxxxxxxxxx>
 S:	Maintained
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/nolibc/linux-nolibc.git
+F:	init/Kconfig.nolibc
+F:	init/Makefile.nolibc
 F:	tools/include/nolibc/
 F:	tools/testing/selftests/nolibc/
 
diff --git a/init/Kconfig b/init/Kconfig
index 3bb92a3f6cc1..c37d9227ba72 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -106,6 +106,8 @@ config CC_CAN_LINK
 	default $(cc_can_link_user,$(m64-flag)) if 64BIT
 	default $(cc_can_link_user,$(m32-flag))
 
+source "init/Kconfig.nolibc"
+
 # Fixed in GCC 14, 13.3, 12.4 and 11.5
 # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113921
 config GCC_ASM_GOTO_OUTPUT_BROKEN
diff --git a/init/Kconfig.nolibc b/init/Kconfig.nolibc
new file mode 100644
index 000000000000..07488ef18f4f
--- /dev/null
+++ b/init/Kconfig.nolibc
@@ -0,0 +1,16 @@
+# SPDX-License-Identifier: GPL-2.0
+
+config ARCH_HAS_NOLIBC
+	bool
+	default y if ARM
+	default y if ARM64
+	default y if LOONGARCH
+	default y if M68K
+	default y if MIPS
+	default y if PPC
+	default y if RISCV
+	default y if S390
+	default y if SPARC
+	default y if SUPERH
+	default y if UML_X86
+	default y if X86
diff --git a/init/Makefile.nolibc b/init/Makefile.nolibc
new file mode 100644
index 000000000000..dacc78ab4c81
--- /dev/null
+++ b/init/Makefile.nolibc
@@ -0,0 +1,13 @@
+# SPDX-License-Identifier: GPL-2.0
+# Compiler flags, which are necessary to build userspace applications with the
+# in-kernel libc "nolibc".
+
+ifeq ($(and $(CONFIG_ARCH_HAS_NOLIBC),$(CONFIG_HEADERS_INSTALL)),y)
+
+NOLIBC_USERCFLAGS := -nostdlib -nostdinc -static -ffreestanding \
+		     -fno-asynchronous-unwind-tables -fno-stack-protector \
+		     -I$(objtree)/usr/include -I$(srctree)/tools/include/nolibc/
+
+NOLIBC_USERLDFLAGS := -nostdlib -nostdinc -static
+
+endif # CONFIG_ARCH_HAS_NOLIBC && CONFIG_HEADERS_INSTALL

-- 
2.53.0