Re: [PATCH v3 3/3] tests/tcg: Add the PROT_NONE gdbstub test

["Alex Bennée" <alex.bennee@linaro.org>]

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

> 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          | 40 ++++++++++++++++++++++++
>  3 files changed, 70 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..f1f1dd82cbe
> --- /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 = gdb.parse_and_eval("*(char[2] *)q").string()

Better traceback:

  Breakpoint 1, break_here (q=0x400000802fff) at /home/alex/lsrc/qemu.git/tests/tcg/multiarch/prot-none.c:14
  14      }
  GDB Exception:
  Traceback (most recent call last):
    File "/home/alex/lsrc/qemu.git/tests/guest-debug/test_gdbstub.py", line 42, in main
      test()
    File "./tests/tcg/multiarch/gdbstub/prot-none.py", line 14, in run_test
      val = gdb.parse_and_eval("*(char[2] *)q").string()
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  gdb.MemoryError: Cannot access memory at address 0x400000802fff
  Python 3.11.2 (main, Mar 13 2023, 12:18:29) [GCC 12.2.0] on linux
  Type "help", "copyright", "credits" or "license" for more information.
  (InteractiveConsole)
  >>> 

> +    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)
> diff --git a/tests/tcg/multiarch/prot-none.c b/tests/tcg/multiarch/prot-none.c
> new file mode 100644
> index 00000000000..dc56aadb3c5
> --- /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;
> +}

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro