tools/nolibc: add support for SuperH

Add support for SuperH/"sh" to nolibc.
Only sh4 is tested for now.

The startup code is special:

__nolibc_entrypoint_epilogue() calls __builtin_unreachable() which emits
a call to abort(). To make this work a function prologue is generated to
set up a GOT pointer which corrupts "sp".
__builtin_unreachable() is necessary for __attribute__((noreturn)).
Also depending on compiler flags (for example -fPIC) even more prologue
is generated.

Work around this by defining a nested function in asm.

Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70216
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Acked-by: Willy Tarreau <w@1wt.eu>
Acked-by: Rob Landley <rob@landley.net>
Acked-by: D. Jeff Dionne <jeff@coresemi.io>
Tested-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Link: https://lore.kernel.org/r/20250623-nolibc-sh-v2-3-0f5b4b303025@weissschuh.net

4 files changed, 173 insertions, 1 deletions

diff --git a/tools/include/nolibc/arch-sh.h b/tools/include/nolibc/arch-sh.h
new file mode 100644
index 000000000000..a96b8914607e
--- /dev/null
+++ b/tools/include/nolibc/arch-sh.h
@@ -0,0 +1,162 @@
+/* SPDX-License-Identifier: LGPL-2.1 OR MIT */
+/*
+ * SuperH specific definitions for NOLIBC
+ * Copyright (C) 2025 Thomas Weißschuh <linux@weissschuh.net>
+ */
+
+#ifndef _NOLIBC_ARCH_SH_H
+#define _NOLIBC_ARCH_SH_H
+
+#include "compiler.h"
+#include "crt.h"
+
+/*
+ * Syscalls for SuperH:
+ *   - registers are 32bit wide
+ *   - syscall number is passed in r3
+ *   - arguments are in r4, r5, r6, r7, r0, r1, r2
+ *   - the system call is performed by calling trapa #31
+ *   - syscall return value is in r0
+ */
+
+#define my_syscall0(num)                                                      \
+({                                                                            \
+	register long _num __asm__ ("r3") = (num);                            \
+	register long _ret __asm__ ("r0");                                    \
+									      \
+	__asm__ volatile (                                                    \
+		"trapa #31"                                                   \
+		: "=r"(_ret)                                                  \
+		: "r"(_num)                                                   \
+		: "memory", "cc"                                              \
+	);                                                                    \
+	_ret;                                                                 \
+})
+
+#define my_syscall1(num, arg1)                                                \
+({                                                                            \
+	register long _num __asm__ ("r3") = (num);                            \
+	register long _ret __asm__ ("r0");                                    \
+	register long _arg1 __asm__ ("r4") = (long)(arg1);                    \
+									      \
+	__asm__ volatile (                                                    \
+		"trapa #31"                                                   \
+		: "=r"(_ret)                                                  \
+		: "r"(_num), "r"(_arg1)                                       \
+		: "memory", "cc"                                              \
+	);                                                                    \
+	_ret;                                                                 \
+})
+
+#define my_syscall2(num, arg1, arg2)                                          \
+({                                                                            \
+	register long _num __asm__ ("r3") = (num);                            \
+	register long _ret __asm__ ("r0");                                    \
+	register long _arg1 __asm__ ("r4") = (long)(arg1);                    \
+	register long _arg2 __asm__ ("r5") = (long)(arg2);                    \
+									      \
+	__asm__ volatile (                                                    \
+		"trapa #31"                                                   \
+		: "=r"(_ret)                                                  \
+		: "r"(_num), "r"(_arg1), "r"(_arg2)                           \
+		: "memory", "cc"                                              \
+	);                                                                    \
+	_ret;                                                                 \
+})
+
+#define my_syscall3(num, arg1, arg2, arg3)                                    \
+({                                                                            \
+	register long _num __asm__ ("r3") = (num);                            \
+	register long _ret __asm__ ("r0");                                    \
+	register long _arg1 __asm__ ("r4") = (long)(arg1);                    \
+	register long _arg2 __asm__ ("r5") = (long)(arg2);                    \
+	register long _arg3 __asm__ ("r6") = (long)(arg3);                    \
+									      \
+	__asm__ volatile (                                                    \
+		"trapa #31"                                                   \
+		: "=r"(_ret)                                                  \
+		: "r"(_num), "r"(_arg1), "r"(_arg2), "r"(_arg3)               \
+		: "memory", "cc"                                              \
+	);                                                                    \
+	_ret;                                                                 \
+})
+
+#define my_syscall4(num, arg1, arg2, arg3, arg4)                              \
+({                                                                            \
+	register long _num __asm__ ("r3") = (num);                            \
+	register long _ret __asm__ ("r0");                                    \
+	register long _arg1 __asm__ ("r4") = (long)(arg1);                    \
+	register long _arg2 __asm__ ("r5") = (long)(arg2);                    \
+	register long _arg3 __asm__ ("r6") = (long)(arg3);                    \
+	register long _arg4 __asm__ ("r7") = (long)(arg4);                    \
+									      \
+	__asm__ volatile (                                                    \
+		"trapa #31"                                                   \
+		: "=r"(_ret)                                                  \
+		: "r"(_num), "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4)   \
+		: "memory", "cc"                                              \
+	);                                                                    \
+	_ret;                                                                 \
+})
+
+#define my_syscall5(num, arg1, arg2, arg3, arg4, arg5)                        \
+({                                                                            \
+	register long _num __asm__ ("r3") = (num);                            \
+	register long _ret __asm__ ("r0");                                    \
+	register long _arg1 __asm__ ("r4") = (long)(arg1);                    \
+	register long _arg2 __asm__ ("r5") = (long)(arg2);                    \
+	register long _arg3 __asm__ ("r6") = (long)(arg3);                    \
+	register long _arg4 __asm__ ("r7") = (long)(arg4);                    \
+	register long _arg5 __asm__ ("r0") = (long)(arg5);                    \
+									      \
+	__asm__ volatile (                                                    \
+		"trapa #31"                                                   \
+		: "=r"(_ret)                                                  \
+		: "r"(_num), "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4),  \
+		  "r"(_arg5)                                                  \
+		: "memory", "cc"                                              \
+	);                                                                    \
+	_ret;                                                                 \
+})
+
+#define my_syscall6(num, arg1, arg2, arg3, arg4, arg5, arg6)                  \
+({                                                                            \
+	register long _num __asm__ ("r3") = (num);                            \
+	register long _ret __asm__ ("r0");                                    \
+	register long _arg1 __asm__ ("r4") = (long)(arg1);                    \
+	register long _arg2 __asm__ ("r5") = (long)(arg2);                    \
+	register long _arg3 __asm__ ("r6") = (long)(arg3);                    \
+	register long _arg4 __asm__ ("r7") = (long)(arg4);                    \
+	register long _arg5 __asm__ ("r0") = (long)(arg5);                    \
+	register long _arg6 __asm__ ("r1") = (long)(arg6);                    \
+									      \
+	__asm__ volatile (                                                    \
+		"trapa #31"                                                   \
+		: "=r"(_ret)                                                  \
+		: "r"(_num), "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4),  \
+		  "r"(_arg5), "r"(_arg6)                                      \
+		: "memory", "cc"                                              \
+	);                                                                    \
+	_ret;                                                                 \
+})
+
+/* startup code */
+void _start_wrapper(void);
+void __attribute__((weak,noreturn)) __nolibc_entrypoint __no_stack_protector _start_wrapper(void)
+{
+	__asm__ volatile (
+		".global _start\n"           /* The C function will have a prologue,         */
+		".type _start, @function\n"  /* corrupting "sp"                              */
+		".weak _start\n"
+		"_start:\n"
+
+		"mov sp, r4\n"               /* save argc pointer to r4, as arg1 of _start_c */
+		"bsr _start_c\n"             /* transfer to c runtime                        */
+		"nop\n"                      /* delay slot                                   */
+
+		".size _start, .-_start\n"
+	);
+	__nolibc_entrypoint_epilogue();
+}
+
+#endif /* _NOLIBC_ARCH_SH_H */
diff --git a/tools/include/nolibc/arch.h b/tools/include/nolibc/arch.h
index db69537c71d8..426c89198135 100644
--- a/tools/include/nolibc/arch.h
+++ b/tools/include/nolibc/arch.h
@@ -35,6 +35,8 @@
 #include "arch-sparc.h"
 #elif defined(__m68k__)
 #include "arch-m68k.h"
+#elif defined(__sh__)
+#include "arch-sh.h"
 #else
 #error Unsupported Architecture
 #endif
diff --git a/tools/testing/selftests/nolibc/Makefile.nolibc b/tools/testing/selftests/nolibc/Makefile.nolibc
index 450d6add864c..cc5ee6c67586 100644
--- a/tools/testing/selftests/nolibc/Makefile.nolibc
+++ b/tools/testing/selftests/nolibc/Makefile.nolibc
@@ -62,6 +62,7 @@ ARCH_riscv64     = riscv
 ARCH_s390x       = s390
 ARCH_sparc32     = sparc
 ARCH_sparc64     = sparc
+ARCH_sh4         = sh
 ARCH            := $(or $(ARCH_$(XARCH)),$(XARCH))
 
 # kernel image names by architecture
@@ -89,6 +90,7 @@ IMAGE_loongarch  = arch/loongarch/boot/vmlinuz.efi
 IMAGE_sparc32    = arch/sparc/boot/image
 IMAGE_sparc64    = arch/sparc/boot/image
 IMAGE_m68k       = vmlinux
+IMAGE_sh4        = arch/sh/boot/zImage
 IMAGE            = $(objtree)/$(IMAGE_$(XARCH))
 IMAGE_NAME       = $(notdir $(IMAGE))
 
@@ -117,11 +119,13 @@ DEFCONFIG_loongarch  = defconfig
 DEFCONFIG_sparc32    = sparc32_defconfig
 DEFCONFIG_sparc64    = sparc64_defconfig
 DEFCONFIG_m68k       = virt_defconfig
+DEFCONFIG_sh4        = rts7751r2dplus_defconfig
 DEFCONFIG            = $(DEFCONFIG_$(XARCH))
 
 EXTRACONFIG_arm       = -e CONFIG_NAMESPACES
 EXTRACONFIG_armthumb  = -e CONFIG_NAMESPACES
 EXTRACONFIG_m68k      = -e CONFIG_BLK_DEV_INITRD
+EXTRACONFIG_sh4       = -e CONFIG_BLK_DEV_INITRD -e CONFIG_CMDLINE_FROM_BOOTLOADER
 EXTRACONFIG           = $(EXTRACONFIG_$(XARCH))
 
 # optional tests to run (default = all)
@@ -152,6 +156,7 @@ QEMU_ARCH_loongarch  = loongarch64
 QEMU_ARCH_sparc32    = sparc
 QEMU_ARCH_sparc64    = sparc64
 QEMU_ARCH_m68k       = m68k
+QEMU_ARCH_sh4        = sh4
 QEMU_ARCH            = $(QEMU_ARCH_$(XARCH))
 
 QEMU_ARCH_USER_ppc64le = ppc64le
@@ -191,6 +196,7 @@ QEMU_ARGS_loongarch  = -M virt -append "console=ttyS0,115200 panic=-1 $(TEST:%=N
 QEMU_ARGS_sparc32    = -M SS-5 -m 256M -append "console=ttyS0,115200 panic=-1 $(TEST:%=NOLIBC_TEST=%)"
 QEMU_ARGS_sparc64    = -M sun4u -append "console=ttyS0,115200 panic=-1 $(TEST:%=NOLIBC_TEST=%)"
 QEMU_ARGS_m68k       = -M virt -append "console=ttyGF0,115200 panic=-1 $(TEST:%=NOLIBC_TEST=%)"
+QEMU_ARGS_sh4        = -M r2d -serial file:/dev/stdout -append "console=ttySC1,115200 panic=-1 $(TEST:%=NOLIBC_TEST=%)"
 QEMU_ARGS            = -m 1G $(QEMU_ARGS_$(XARCH)) $(QEMU_ARGS_BIOS) $(QEMU_ARGS_EXTRA)
 
 # OUTPUT is only set when run from the main makefile, otherwise
@@ -218,6 +224,7 @@ CFLAGS_mipsn32be = -EB -mabi=n32 -march=mips64r6
 CFLAGS_mips64le = -EL -mabi=64 -march=mips64r6
 CFLAGS_mips64be = -EB -mabi=64 -march=mips64r2
 CFLAGS_sparc32 = $(call cc-option,-m32)
+CFLAGS_sh4 = -ml -m4
 ifeq ($(origin XARCH),command line)
 CFLAGS_XARCH = $(CFLAGS_$(XARCH))
 endif
diff --git a/tools/testing/selftests/nolibc/run-tests.sh b/tools/testing/selftests/nolibc/run-tests.sh
index fc8351994566..43eb30be316a 100755
--- a/tools/testing/selftests/nolibc/run-tests.sh
+++ b/tools/testing/selftests/nolibc/run-tests.sh
@@ -27,6 +27,7 @@ all_archs=(
 	loongarch
 	sparc32 sparc64
 	m68k
+	sh4
 )
 archs="${all_archs[@]}"
 
@@ -187,7 +188,7 @@ test_arch() {
 		echo "Unsupported configuration"
 		return
 	fi
-	if [ "$arch" = "m68k" ] && [ "$llvm" = "1" ]; then
+	if [ "$arch" = "m68k" -o "$arch" = "sh4" ] && [ "$llvm" = "1" ]; then
 		echo "Unsupported configuration"
 		return
 	fi