tools/nolibc: add support for 32-bit s390

32-bit s390 is very close to the existing 64-bit implementation.

Some special handling is necessary as there is neither LLVM nor
QEMU support. Also the kernel itself can not build natively for 32-bit
s390, so instead the test program is executed with a 64-bit kernel.

Acked-by: Willy Tarreau <w@1wt.eu>
Link: https://lore.kernel.org/r/20250206-nolibc-s390-v2-2-991ad97e3d58@weissschuh.net
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>

Author: t-8ch

tools/include/nolibc/arch-s390.h

@@ -143,8 +143,13 @@
 void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector _start(void)
 {
 	__asm__ volatile (
+#ifdef __s390x__
 		"lgr	%r2, %r15\n"          /* save stack pointer to %r2, as arg1 of _start_c */
 		"aghi	%r15, -160\n"         /* allocate new stackframe                        */
+#else
+		"lr	%r2, %r15\n"
+		"ahi	%r15, -96\n"
+#endif
 		"xc	0(8,%r15), 0(%r15)\n" /* clear backchain                                */
 		"brasl	%r14, _start_c\n"     /* transfer to c runtime                          */
 	);

tools/include/nolibc/arch.h

@@ -29,7 +29,7 @@
 #include "arch-powerpc.h"
 #elif defined(__riscv)
 #include "arch-riscv.h"
-#elif defined(__s390x__)
+#elif defined(__s390x__) || defined(__s390__)
 #include "arch-s390.h"
 #elif defined(__loongarch__)
 #include "arch-loongarch.h"

tools/testing/selftests/nolibc/Makefile

@@ -72,6 +72,7 @@ IMAGE_riscv      = arch/riscv/boot/Image
 IMAGE_riscv32    = arch/riscv/boot/Image
 IMAGE_riscv64    = arch/riscv/boot/Image
 IMAGE_s390x      = arch/s390/boot/bzImage
+IMAGE_s390       = arch/s390/boot/bzImage
 IMAGE_loongarch  = arch/loongarch/boot/vmlinuz.efi
 IMAGE            = $(objtree)/$(IMAGE_$(XARCH))
 IMAGE_NAME       = $(notdir $(IMAGE))
@@ -91,6 +92,7 @@ DEFCONFIG_riscv      = defconfig
 DEFCONFIG_riscv32    = rv32_defconfig
 DEFCONFIG_riscv64    = defconfig
 DEFCONFIG_s390x      = defconfig
+DEFCONFIG_s390       = defconfig compat.config
 DEFCONFIG_loongarch  = defconfig
 DEFCONFIG            = $(DEFCONFIG_$(XARCH))
 
@@ -114,6 +116,7 @@ QEMU_ARCH_riscv      = riscv64
 QEMU_ARCH_riscv32    = riscv32
 QEMU_ARCH_riscv64    = riscv64
 QEMU_ARCH_s390x      = s390x
+QEMU_ARCH_s390       = s390x
 QEMU_ARCH_loongarch  = loongarch64
 QEMU_ARCH            = $(QEMU_ARCH_$(XARCH))
 
@@ -142,6 +145,7 @@ QEMU_ARGS_riscv      = -M virt -append "console=ttyS0 panic=-1 $(TEST:%=NOLIBC_T
 QEMU_ARGS_riscv32    = -M virt -append "console=ttyS0 panic=-1 $(TEST:%=NOLIBC_TEST=%)"
 QEMU_ARGS_riscv64    = -M virt -append "console=ttyS0 panic=-1 $(TEST:%=NOLIBC_TEST=%)"
 QEMU_ARGS_s390x      = -M s390-ccw-virtio -append "console=ttyS0 panic=-1 $(TEST:%=NOLIBC_TEST=%)"
+QEMU_ARGS_s390       = -M s390-ccw-virtio -append "console=ttyS0 panic=-1 $(TEST:%=NOLIBC_TEST=%)"
 QEMU_ARGS_loongarch  = -M virt -append "console=ttyS0,115200 panic=-1 $(TEST:%=NOLIBC_TEST=%)"
 QEMU_ARGS            = -m 1G $(QEMU_ARGS_$(XARCH)) $(QEMU_ARGS_BIOS) $(QEMU_ARGS_EXTRA)
 
@@ -160,6 +164,7 @@ CFLAGS_ppc = -m32 -mbig-endian -mno-vsx $(call cc-option,-mmultiple)
 CFLAGS_ppc64 = -m64 -mbig-endian -mno-vsx $(call cc-option,-mmultiple)
 CFLAGS_ppc64le = -m64 -mlittle-endian -mno-vsx $(call cc-option,-mabi=elfv2)
 CFLAGS_s390x = -m64
+CFLAGS_s390 = -m31
 CFLAGS_mips32le = -EL -mabi=32 -fPIC
 CFLAGS_mips32be = -EB -mabi=32
 CFLAGS_STACKPROTECTOR ?= $(call cc-option,-mstack-protector-guard=global $(call cc-option,-fstack-protector-all))

tools/testing/selftests/nolibc/run-tests.sh

@@ -23,7 +23,7 @@ all_archs=(
 	mips32le mips32be
 	ppc ppc64 ppc64le
 	riscv32 riscv64
-	s390x
+	s390x s390
 	loongarch
 )
 archs="${all_archs[@]}"
@@ -179,6 +179,10 @@ test_arch() {
 			exit 1
 	esac
 	printf '%-15s' "$arch:"
+	if [ "$arch" = "s390" ] && ([ "$llvm" = "1" ] || [ "$test_mode" = "user" ]); then
+		echo "Unsupported configuration"
+		return
+	fi
 
 	mkdir -p "$build_dir"
 	swallow_output "${MAKE[@]}" defconfig