Register a syscall filter callback in tests/tcg/plugins/sycall.c,
returns a specific value for a magic system call number, and check
it in tests/tcg/multiarch/test-plugin-syscall-filter.c.

Signed-off-by: Ziyang Zhang <functioner@sjtu.edu.cn>
Co-authored-by: Mingyuan Xia <xiamy@ultrarisc.com>
---
 tests/tcg/multiarch/Makefile.target           |  4 ++-
 .../multiarch/test-plugin-syscall-filter.c    | 35 +++++++++++++++++++
 tests/tcg/plugins/syscall.c                   | 19 ++++++++++
 3 files changed, 57 insertions(+), 1 deletion(-)
 create mode 100644 tests/tcg/multiarch/test-plugin-syscall-filter.c

diff --git a/tests/tcg/multiarch/Makefile.target b/tests/tcg/multiarch/Makefile.target
index f5b4d2b813..4005e3a8a9 100644
--- a/tests/tcg/multiarch/Makefile.target
+++ b/tests/tcg/multiarch/Makefile.target
@@ -202,8 +202,10 @@ run-plugin-test-plugin-mem-access-with-libmem.so: \
 	CHECK_PLUGIN_OUTPUT_COMMAND= \
 	$(SRC_PATH)/tests/tcg/multiarch/check-plugin-output.sh \
 	$(QEMU) $<
+run-plugin-test-plugin-syscall-filter-with-libsyscall.so:
 
-EXTRA_RUNS_WITH_PLUGIN += run-plugin-test-plugin-mem-access-with-libmem.so
+EXTRA_RUNS_WITH_PLUGIN += run-plugin-test-plugin-mem-access-with-libmem.so \
+			   			  run-plugin-test-plugin-syscall-filter-with-libsyscall.so
 endif
 
 # Update TESTS
diff --git a/tests/tcg/multiarch/test-plugin-syscall-filter.c b/tests/tcg/multiarch/test-plugin-syscall-filter.c
new file mode 100644
index 0000000000..caa2063a46
--- /dev/null
+++ b/tests/tcg/multiarch/test-plugin-syscall-filter.c
@@ -0,0 +1,35 @@
+/*
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ *
+ * This test attempts to execute a magic syscall. The syscall test plugin
+ * should intercept this and return an expected value.
+ */
+
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+int main(int argc, char *argv[])
+{
+    /*
+     * We cannot use a very large magic syscall number, because on some ISAs,
+     * QEMU will treat it as an illegal instruction and trigger a critical
+     * exception. For instance, on arm32, the syscall number cannot exceed
+     * ARM_NR_BASE (0xf0000), as can be seen in
+     * "linux-user/arm/cpu_loop.c:cpu_loop".
+     *
+     * Therefore, we pick 2048 because, as of now, no ISA in Linux uses this
+     * number. This is just a test case; replace this number as needed in the
+     * future.
+     *
+     * The corresponding syscall filter is implemented in
+     * "tests/tcg/plugins/syscall.c".
+     */
+    long ret = syscall(2048, 0x66CCFF);
+    if (ret != 0xFFCC66) {
+        fprintf(stderr, "Error: unexpected syscall return value %ld\n", ret);
+        return EXIT_FAILURE;
+    }
+    return EXIT_SUCCESS;
+}
diff --git a/tests/tcg/plugins/syscall.c b/tests/tcg/plugins/syscall.c
index 42801f5c86..e7d4e9b589 100644
--- a/tests/tcg/plugins/syscall.c
+++ b/tests/tcg/plugins/syscall.c
@@ -170,6 +170,24 @@ static void vcpu_syscall_ret(qemu_plugin_id_t id, unsigned int vcpu_idx,
     }
 }
 
+static bool vcpu_syscall_filter(qemu_plugin_id_t id, unsigned int vcpu_index,
+                                int64_t num, uint64_t a1, uint64_t a2,
+                                uint64_t a3, uint64_t a4, uint64_t a5,
+                                uint64_t a6, uint64_t a7, uint64_t a8,
+                                uint64_t *sysret)
+{
+    /* Special syscall to test the filter functionality. */
+    if (num == 2048 && a1 == 0x66CCFF) {
+        *sysret = 0xFFCC66;
+
+        if (!statistics) {
+            qemu_plugin_outs("magic syscall filtered, set magic return\n");
+        }
+        return true;
+    }
+    return false;
+}
+
 static void print_entry(gpointer val, gpointer user_data)
 {
     SyscallStats *entry = (SyscallStats *) val;
@@ -255,6 +273,7 @@ QEMU_PLUGIN_EXPORT int qemu_plugin_install(qemu_plugin_id_t id,
 
     qemu_plugin_register_vcpu_syscall_cb(id, vcpu_syscall);
     qemu_plugin_register_vcpu_syscall_ret_cb(id, vcpu_syscall_ret);
+    qemu_plugin_register_vcpu_syscall_filter_cb(id, vcpu_syscall_filter);
     qemu_plugin_register_atexit_cb(id, plugin_exit, NULL);
     return 0;
 }
-- 
2.34.1