Make sure that qemu gdbstub, like gdbserver, allows reading from and
writing to PROT_NONE pages.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 tests/tcg/multiarch/Makefile.target      |  9 +++++-
 tests/tcg/multiarch/gdbstub/prot-none.py | 22 ++++++++++++++
 tests/tcg/multiarch/prot-none.c          | 38 ++++++++++++++++++++++++
 3 files changed, 68 insertions(+), 1 deletion(-)
 create mode 100644 tests/tcg/multiarch/gdbstub/prot-none.py
 create mode 100644 tests/tcg/multiarch/prot-none.c

diff --git a/tests/tcg/multiarch/Makefile.target b/tests/tcg/multiarch/Makefile.target
index d31ba8d6ae4..315a2e13588 100644
--- a/tests/tcg/multiarch/Makefile.target
+++ b/tests/tcg/multiarch/Makefile.target
@@ -101,13 +101,20 @@ run-gdbstub-registers: sha512
 		--bin $< --test $(MULTIARCH_SRC)/gdbstub/registers.py, \
 	checking register enumeration)
 
+run-gdbstub-prot-none: prot-none
+	$(call run-test, $@, env PROT_NONE_PY=1 $(GDB_SCRIPT) \
+		--gdb $(GDB) \
+		--qemu $(QEMU) --qargs "$(QEMU_OPTS)" \
+		--bin $< --test $(MULTIARCH_SRC)/gdbstub/prot-none.py, \
+	accessing PROT_NONE memory)
+
 else
 run-gdbstub-%:
 	$(call skip-test, "gdbstub test $*", "need working gdb with $(patsubst -%,,$(TARGET_NAME)) support")
 endif
 EXTRA_RUNS += run-gdbstub-sha1 run-gdbstub-qxfer-auxv-read \
 	      run-gdbstub-proc-mappings run-gdbstub-thread-breakpoint \
-	      run-gdbstub-registers
+	      run-gdbstub-registers run-gdbstub-prot-none
 
 # ARM Compatible Semi Hosting Tests
 #
diff --git a/tests/tcg/multiarch/gdbstub/prot-none.py b/tests/tcg/multiarch/gdbstub/prot-none.py
new file mode 100644
index 00000000000..751e44d5b93
--- /dev/null
+++ b/tests/tcg/multiarch/gdbstub/prot-none.py
@@ -0,0 +1,22 @@
+"""Test that GDB can access PROT_NONE pages.
+
+This runs as a sourced script (via -x, via run-test.py).
+
+SPDX-License-Identifier: GPL-2.0-or-later
+"""
+from test_gdbstub import main, report
+
+
+def run_test():
+    """Run through the tests one by one"""
+    gdb.Breakpoint("break_here")
+    gdb.execute("continue")
+    val = int(gdb.parse_and_eval("*p"))
+    report(val == 42, "{} != 42".format(val))
+    gdb.execute("set *p = 24")
+    gdb.execute("continue")
+    exitcode = int(gdb.parse_and_eval("$_exitcode"))
+    report(exitcode == 0, "{} != 0".format(exitcode))
+
+
+main(run_test)
diff --git a/tests/tcg/multiarch/prot-none.c b/tests/tcg/multiarch/prot-none.c
new file mode 100644
index 00000000000..66e38065cf0
--- /dev/null
+++ b/tests/tcg/multiarch/prot-none.c
@@ -0,0 +1,38 @@
+/*
+ * Test that GDB can access PROT_NONE pages.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+#include <assert.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+void break_here(long *p)
+{
+}
+
+int main(void)
+{
+    long pagesize = sysconf(_SC_PAGESIZE);
+    int err;
+    long *p;
+
+    p = mmap(NULL, pagesize, PROT_READ | PROT_WRITE,
+             MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+    assert(p != MAP_FAILED);
+    *p = 42;
+
+    err = mprotect(p, pagesize, PROT_NONE);
+    assert(err == 0);
+
+    break_here(p);
+
+    err = mprotect(p, pagesize, PROT_READ);
+    assert(err == 0);
+    if (getenv("PROT_NONE_PY")) {
+        assert(*p == 24);
+    }
+
+    return EXIT_SUCCESS;
+}
-- 
2.43.0