From: Ilya Leoshkevich <iii@linux.ibm.com>

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>
Message-Id: <20240129093410.3151-4-iii@linux.ibm.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 tests/tcg/multiarch/prot-none.c          | 40 ++++++++++++++++++++++++
 tests/tcg/multiarch/Makefile.target      |  9 +++++-
 tests/tcg/multiarch/gdbstub/prot-none.py | 36 +++++++++++++++++++++
 3 files changed, 84 insertions(+), 1 deletion(-)
 create mode 100644 tests/tcg/multiarch/prot-none.c
 create mode 100644 tests/tcg/multiarch/gdbstub/prot-none.py

diff --git a/tests/tcg/multiarch/prot-none.c b/tests/tcg/multiarch/prot-none.c
new file mode 100644
index 0000000000..dc56aadb3c
--- /dev/null
+++ b/tests/tcg/multiarch/prot-none.c
@@ -0,0 +1,40 @@
+/*
+ * Test that GDB can access PROT_NONE pages.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+#include <assert.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+void break_here(void *q)
+{
+}
+
+int main(void)
+{
+    long pagesize = sysconf(_SC_PAGESIZE);
+    void *p, *q;
+    int err;
+
+    p = mmap(NULL, pagesize * 2, PROT_READ | PROT_WRITE,
+             MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+    assert(p != MAP_FAILED);
+    q = p + pagesize - 1;
+    strcpy(q, "42");
+
+    err = mprotect(p, pagesize * 2, PROT_NONE);
+    assert(err == 0);
+
+    break_here(q);
+
+    err = mprotect(p, pagesize * 2, PROT_READ);
+    assert(err == 0);
+    if (getenv("PROT_NONE_PY")) {
+        assert(strcmp(q, "24") == 0);
+    }
+
+    return EXIT_SUCCESS;
+}
diff --git a/tests/tcg/multiarch/Makefile.target b/tests/tcg/multiarch/Makefile.target
index d31ba8d6ae..315a2e1358 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 0000000000..e829d3ebc5
--- /dev/null
+++ b/tests/tcg/multiarch/gdbstub/prot-none.py
@@ -0,0 +1,36 @@
+"""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
+"""
+import ctypes
+from test_gdbstub import main, report
+
+
+def probe_proc_self_mem():
+    buf = ctypes.create_string_buffer(b'aaa')
+    try:
+        with open("/proc/self/mem", "rb") as fp:
+            fp.seek(ctypes.addressof(buf))
+            return fp.read(3) == b'aaa'
+    except OSError:
+        return False
+
+
+def run_test():
+    """Run through the tests one by one"""
+    if not probe_proc_self_mem:
+        print("SKIP: /proc/self/mem is not usable")
+        exit(0)
+    gdb.Breakpoint("break_here")
+    gdb.execute("continue")
+    val = gdb.parse_and_eval("*(char[2] *)q").string()
+    report(val == "42", "{} == 42".format(val))
+    gdb.execute("set *(char[3] *)q = \"24\"")
+    gdb.execute("continue")
+    exitcode = int(gdb.parse_and_eval("$_exitcode"))
+    report(exitcode == 0, "{} == 0".format(exitcode))
+
+
+main(run_test)
-- 
2.34.1

On Tue, 2024-01-30 at 09:01 +1000, Richard Henderson wrote:
> From: Ilya Leoshkevich <iii@linux.ibm.com>
> 
> 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>
> Message-Id: <20240129093410.3151-4-iii@linux.ibm.com>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  tests/tcg/multiarch/prot-none.c          | 40
> ++++++++++++++++++++++++
>  tests/tcg/multiarch/Makefile.target      |  9 +++++-
>  tests/tcg/multiarch/gdbstub/prot-none.py | 36 +++++++++++++++++++++
>  3 files changed, 84 insertions(+), 1 deletion(-)
>  create mode 100644 tests/tcg/multiarch/prot-none.c
>  create mode 100644 tests/tcg/multiarch/gdbstub/prot-none.py

[...]

> diff --git a/tests/tcg/multiarch/gdbstub/prot-none.py
> b/tests/tcg/multiarch/gdbstub/prot-none.py
> new file mode 100644
> index 0000000000..e829d3ebc5
> --- /dev/null
> +++ b/tests/tcg/multiarch/gdbstub/prot-none.py
> @@ -0,0 +1,36 @@
> +"""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
> +"""
> +import ctypes
> +from test_gdbstub import main, report
> +
> +
> +def probe_proc_self_mem():
> +    buf = ctypes.create_string_buffer(b'aaa')
> +    try:
> +        with open("/proc/self/mem", "rb") as fp:
> +            fp.seek(ctypes.addressof(buf))
> +            return fp.read(3) == b'aaa'
> +    except OSError:
> +        return False
> +
> +
> +def run_test():
> +    """Run through the tests one by one"""
> +    if not probe_proc_self_mem:

I noticed that I made an embarrassing typo here: this should be
`not probe_proc_self_mem()`. I posted a v5 with the correction.

[...]