tests/tcg/s390x: Test modifying an EXECUTE target

QEMU correctly implements the tracking of EXECUTE target modifications
by storing the instruction text in env->ex_value and tb->cs_base, the
latter of which is used for lookups.

Still, EXECUTE is a tricky corner of the s390x emulation, which can
benefit from having a regression test.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-ID: <20241001145634.9786-1-iii@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

tests/tcg/s390x/Makefile.target

@@ -48,6 +48,7 @@ TESTS+=lae
 TESTS+=cvd
 TESTS+=cvb
 TESTS+=ts
+TESTS+=ex-smc
 
 cdsg: CFLAGS+=-pthread
 cdsg: LDFLAGS+=-pthread

tests/tcg/s390x/ex-smc.c

@@ -0,0 +1,57 @@
+/*
+ * Test modifying an EXECUTE target.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+#include <assert.h>
+#include <stdlib.h>
+
+/* Make sure we exercise the same EXECUTE instruction. */
+extern void execute(unsigned char *insn, unsigned char mask,
+                    unsigned long *r1_r5);
+asm(".globl execute\n"
+    "execute:\n"
+    "lg %r1,0(%r4)\n"
+    "lg %r5,8(%r4)\n"
+    "ex %r3,0(%r2)\n"
+    "stg %r5,8(%r4)\n"
+    "stg %r1,0(%r4)\n"
+    "br %r14\n");
+
+/* Define an RWX EXECUTE target. */
+extern unsigned char lgfi[];
+asm(".pushsection .rwx,\"awx\",@progbits\n"
+    ".globl lgfi\n"
+    "lgfi: lgfi %r0,0\n"
+    ".popsection\n");
+
+int main(void)
+{
+    unsigned long r1_r5[2];
+
+    /* Create an initial TB. */
+    r1_r5[0] = -1;
+    r1_r5[1] = -1;
+    execute(lgfi, 1 << 4, r1_r5);
+    assert(r1_r5[0] == 0);
+    assert(r1_r5[1] == -1);
+
+    /* Test changing the mask. */
+    execute(lgfi, 5 << 4, r1_r5);
+    assert(r1_r5[0] == 0);
+    assert(r1_r5[1] == 0);
+
+    /* Test changing the target. */
+    lgfi[5] = 42;
+    execute(lgfi, 5 << 4, r1_r5);
+    assert(r1_r5[0] == 0);
+    assert(r1_r5[1] == 42);
+
+    /* Test changing both the mask and the target. */
+    lgfi[5] = 24;
+    execute(lgfi, 1 << 4, r1_r5);
+    assert(r1_r5[0] == 24);
+    assert(r1_r5[1] == 42);
+
+    return EXIT_SUCCESS;
+}