tests/tcg: enable basic testing for aarch64_be-linux-user

We didn't notice breakage of aarch64_be because we don't have any TCG
tests for it. However while the existing aarch64 compiler can target
big-endian builds no one packages a BE libc. Instead we bang some
rocks together to do the most basic of hello world with a nostdlib
syscall test.

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20241023113406.1284676-14-alex.bennee@linaro.org>

configure

@@ -1418,6 +1418,7 @@ probe_target_compiler() {
   target_arch=${1%%-*}
   case $target_arch in
     aarch64) container_hosts="x86_64 aarch64" ;;
+    aarch64_be) container_hosts="x86_64 aarch64" ;;
     alpha) container_hosts=x86_64 ;;
     arm) container_hosts="x86_64 aarch64" ;;
     hexagon) container_hosts=x86_64 ;;
@@ -1447,6 +1448,10 @@ probe_target_compiler() {
     case $target_arch in
       # debian-all-test-cross architectures
 
+      aarch64_be)
+        container_image=debian-all-test-cross
+        container_cross_prefix=aarch64-linux-gnu-
+        ;;
       hppa|m68k|mips|riscv64|sparc64)
         container_image=debian-all-test-cross
         ;;

tests/tcg/Makefile.target

@@ -103,9 +103,14 @@ ifeq ($(filter %-softmmu, $(TARGET)),)
 # then the target. If there are common tests shared between
 # sub-targets (e.g. ARM & AArch64) then it is up to
 # $(TARGET_NAME)/Makefile.target to include the common parent
-# architecture in its VPATH.
+# architecture in its VPATH. However some targets are so minimal we
+# can't even build the multiarch tests.
+ifneq ($(filter $(TARGET_NAME),aarch64_be),)
+-include $(SRC_PATH)/tests/tcg/$(TARGET_NAME)/Makefile.target
+else
 -include $(SRC_PATH)/tests/tcg/multiarch/Makefile.target
 -include $(SRC_PATH)/tests/tcg/$(TARGET_NAME)/Makefile.target
+endif
 
 # Add the common build options
 CFLAGS+=-Wall -Werror -O0 -g -fno-strict-aliasing

tests/tcg/aarch64_be/Makefile.target

@@ -0,0 +1,17 @@
+# -*- Mode: makefile -*-
+#
+# A super basic AArch64 BE makefile. As we don't have any big-endian
+# libc available the best we can do is a basic Hello World.
+
+AARCH64BE_SRC=$(SRC_PATH)/tests/tcg/aarch64_be
+VPATH += $(AARCH64BE_SRC)
+
+AARCH64BE_TEST_SRCS=$(notdir $(wildcard $(AARCH64BE_SRC)/*.c))
+AARCH64BE_TESTS=$(AARCH64BE_TEST_SRCS:.c=)
+#MULTIARCH_TESTS = $(MULTIARCH_SRCS:.c=)
+
+# We need to specify big-endian cflags
+CFLAGS +=-mbig-endian -ffreestanding
+LDFLAGS +=-nostdlib
+
+TESTS += $(AARCH64BE_TESTS)

tests/tcg/aarch64_be/hello.c

@@ -0,0 +1,35 @@
+/*
+ * Non-libc syscall hello world for Aarch64 BE
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#define __NR_write 64
+#define __NR_exit 93
+
+int write(int fd, char *buf, int len)
+{
+    register int x0 __asm__("x0") = fd;
+    register char *x1 __asm__("x1") = buf;
+    register int x2 __asm__("x2") = len;
+    register int x8 __asm__("x8") = __NR_write;
+
+    asm volatile("svc #0" : : "r"(x0), "r"(x1), "r"(x2), "r"(x8));
+
+    return len;
+}
+
+void exit(int ret)
+{
+    register int x0 __asm__("x0") = ret;
+    register int x8 __asm__("x8") = __NR_exit;
+
+    asm volatile("svc #0" : : "r"(x0), "r"(x8));
+    __builtin_unreachable();
+}
+
+void _start(void)
+{
+    write(1, "Hello World\n", 12);
+    exit(0);
+}