[v3,15/15] tests/acceptance: add reverse debugging test

From: Pavel Dovgalyuk <Pavel.Dovgaluk@gmail.com>

This is a test for GDB reverse debugging commands: reverse step and reverse continue.
Every test in this suite consists of two phases: record and replay.
Recording saves the execution of some instructions and makes an initial
VM snapshot to allow reverse execution.
Replay saves the order of the first instructions and then checks that they
are executed backwards in the correct order.
After that the execution is replayed to the end, and reverse continue
command is checked by setting several breakpoints, and asserting
that the execution is stopped at the last of them.

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
---
 MAINTAINERS                           |    1 
 tests/acceptance/reverse_debugging.py |  203 +++++++++++++++++++++++++++++++++
 2 files changed, 204 insertions(+)
 create mode 100644 tests/acceptance/reverse_debugging.py

Pavel Dovgalyuk <pavel.dovgalyuk@ispras.ru> writes:

> From: Pavel Dovgalyuk <Pavel.Dovgaluk@gmail.com>
>
> This is a test for GDB reverse debugging commands: reverse step and reverse continue.
> Every test in this suite consists of two phases: record and replay.
> Recording saves the execution of some instructions and makes an initial
> VM snapshot to allow reverse execution.
> Replay saves the order of the first instructions and then checks that they
> are executed backwards in the correct order.
> After that the execution is replayed to the end, and reverse continue
> command is checked by setting several breakpoints, and asserting
> that the execution is stopped at the last of them.
>
> Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
> ---
>  MAINTAINERS                           |    1 
>  tests/acceptance/reverse_debugging.py |  203 +++++++++++++++++++++++++++++++++
>  2 files changed, 204 insertions(+)
>  create mode 100644 tests/acceptance/reverse_debugging.py
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index e49af700c9..76450f1bdf 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -2644,6 +2644,7 @@ F: include/sysemu/replay.h
>  F: docs/replay.txt
>  F: stubs/replay.c
>  F: tests/acceptance/replay_kernel.py
> +F: tests/acceptance/reverse_debugging.py
>  F: qapi/replay.json
>  
>  IOVA Tree
> diff --git a/tests/acceptance/reverse_debugging.py b/tests/acceptance/reverse_debugging.py
> new file mode 100644
> index 0000000000..dda42e1c1a
> --- /dev/null
> +++ b/tests/acceptance/reverse_debugging.py
> @@ -0,0 +1,203 @@
> +# Reverse debugging test
> +#
> +# Copyright (c) 2020 ISP RAS
> +#
> +# Author:
> +#  Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
> +#
> +# This work is licensed under the terms of the GNU GPL, version 2 or
> +# later.  See the COPYING file in the top-level directory.
> +import os
> +import logging
> +
> +from avocado_qemu import BUILD_DIR
> +from avocado.utils import gdb
> +from avocado.utils import process
> +from avocado.utils.path import find_command
> +from boot_linux_console import LinuxKernelTest
> +
> +class ReverseDebugging(LinuxKernelTest):
> +    """
> +    Test GDB reverse debugging commands: reverse step and reverse continue.
> +    Recording saves the execution of some instructions and makes an initial
> +    VM snapshot to allow reverse execution.
> +    Replay saves the order of the first instructions and then checks that they
> +    are executed backwards in the correct order.
> +    After that the execution is replayed to the end, and reverse continue
> +    command is checked by setting several breakpoints, and asserting
> +    that the execution is stopped at the last of them.
> +    """
> +
> +    timeout = 10
> +    STEPS = 10
> +    endian_is_le = True
> +
> +    def run_vm(self, record, shift, args, replay_path, image_path):
> +        logger = logging.getLogger('replay')
> +        vm = self.get_vm()
> +        vm.set_console()
> +        if record:
> +            logger.info('recording the execution...')
> +            mode = 'record'
> +        else:
> +            logger.info('replaying the execution...')
> +            mode = 'replay'
> +            vm.add_args('-s', '-S')
> +        vm.add_args('-icount', 'shift=%s,rr=%s,rrfile=%s,rrsnapshot=init' %
> +                    (shift, mode, replay_path),
> +                    '-net', 'none')
> +        vm.add_args('-drive', 'file=%s,if=none' % image_path)
> +        if args:
> +            vm.add_args(*args)
> +        vm.launch()
> +        return vm
> +
> +    @staticmethod
> +    def get_reg_le(g, reg):
> +        res = g.cmd(b'p%x' % reg)
> +        num = 0
> +        for i in range(len(res))[-2::-2]:
> +            num = 0x100 * num + int(res[i:i + 2], 16)
> +        return num
> +
> +    @staticmethod
> +    def get_reg_be(g, reg):
> +        res = g.cmd(b'p%x' % reg)
> +        return int(res, 16)
> +
> +    def get_reg(self, g, reg):
> +        # value may be encoded in BE or LE order
> +        if self.endian_is_le:
> +            return self.get_reg_le(g, reg)
> +        else:
> +            return self.get_reg_be(g, reg)

These seem a little hacky. Can't we issue normal gdb commands. In the
SVE tests I use:

    frame = gdb.selected_frame()
    for i in range(0, 32):
        rname = "z%d" % (i)
        zreg = frame.read_register(rname)

which works with the symbolic name and doesn't need endian tricks to
sort it out.

> +
> +    def get_pc(self, g):
> +        return self.get_reg(g, self.REG_PC)
> +
> +    def check_pc(self, g, addr):
> +        pc = self.get_pc(g)
> +        if pc != addr:
> +            self.fail('Invalid PC (read %x instead of %x)' % (pc, addr))
> +
> +    @staticmethod
> +    def gdb_step(g):
> +        g.cmd(b's', b'T05thread:01;')
> +
> +    @staticmethod
> +    def gdb_bstep(g):
> +        g.cmd(b'bs', b'T05thread:01;')

Hmm so these are packet commands? Can't we access via the python API? Clebber?

> +
> +    @staticmethod
> +    def vm_get_icount(vm):
> +        return vm.qmp('query-replay')['return']['icount']
> +
> +    def reverse_debugging(self, shift=7, args=None):
> +        logger = logging.getLogger('replay')
> +
> +        # create qcow2 for snapshots
> +        logger.info('creating qcow2 image for VM snapshots')
> +        image_path = os.path.join(self.workdir, 'disk.qcow2')
> +        qemu_img = os.path.join(BUILD_DIR, 'qemu-img')
> +        if not os.path.exists(qemu_img):
> +            qemu_img = find_command('qemu-img', False)
> +        if qemu_img is False:
> +            self.cancel('Could not find "qemu-img", which is required to '
> +                        'create the temporary qcow2 image')
> +        cmd = '%s create -f qcow2 %s 128M' % (qemu_img, image_path)
> +        process.run(cmd)
> +
> +        replay_path = os.path.join(self.workdir, 'replay.bin')
> +
> +        # record the log
> +        vm = self.run_vm(True, shift, args, replay_path, image_path)
> +        while self.vm_get_icount(vm) <= self.STEPS:
> +            pass
> +        last_icount = self.vm_get_icount(vm)
> +        vm.shutdown()
> +
> +        logger.info("recorded log with %s+ steps" % last_icount)
> +
> +        # replay and run debug commands
> +        vm = self.run_vm(False, shift, args, replay_path, image_path)
> +        logger.info('connecting to gdbstub')
> +        g = gdb.GDBRemote('127.0.0.1', 1234, False, False)
> +        g.connect()
> +        r = g.cmd(b'qSupported')
> +        if b'qXfer:features:read+' in r:
> +            g.cmd(b'qXfer:features:read:target.xml:0,ffb')
> +        if b'ReverseStep+' not in r:
> +            self.fail('Reverse step is not supported by QEMU')
> +        if b'ReverseContinue+' not in r:
> +            self.fail('Reverse continue is not supported by QEMU')
> +
> +        logger.info('stepping forward')
> +        steps = []
> +        # record first instruction addresses
> +        for _ in range(self.STEPS):
> +            pc = self.get_pc(g)
> +            logger.info('saving position %x' % pc)
> +            steps.append(pc)
> +            self.gdb_step(g)
> +
> +        # visit the recorded instruction in reverse order
> +        logger.info('stepping backward')
> +        for addr in steps[::-1]:
> +            self.gdb_bstep(g)
> +            self.check_pc(g, addr)
> +            logger.info('found position %x' % addr)
> +
> +        logger.info('seeking to the end (icount %s)' % (last_icount - 1))
> +        vm.qmp('replay-break', icount=last_icount - 1)
> +        # continue - will return after pausing
> +        g.cmd(b'c', b'T02thread:01;')
> +
> +        logger.info('setting breakpoints')
> +        for addr in steps:
> +            # hardware breakpoint at addr with len=1
> +            g.cmd(b'Z1,%x,1' % addr, b'OK')
> +
> +        logger.info('running reverse continue to reach %x' % steps[-1])
> +        # reverse continue - will return after stopping at the breakpoint
> +        g.cmd(b'bc', b'T05thread:01;')
> +
> +        # assume that none of the first instructions is executed again
> +        # breaking the order of the breakpoints
> +        self.check_pc(g, steps[-1])
> +        logger.info('successfully reached %x' % steps[-1])
> +
> +        logger.info('exitting gdb and qemu')
> +        vm.shutdown()
> +
> +class ReverseDebugging_X86_64(ReverseDebugging):
> +    REG_PC = 0x10
> +    REG_CS = 0x12
> +    def get_pc(self, g):
> +        return self.get_reg_le(g, self.REG_PC) \
> +            + self.get_reg_le(g, self.REG_CS) * 0x10
> +
> +    def test_x86_64_pc(self):
> +        """
> +        :avocado: tags=arch:x86_64
> +        :avocado: tags=machine:pc
> +        """
> +        # start with BIOS only
> +        self.reverse_debugging()
> +
> +class ReverseDebugging_AArch64(ReverseDebugging):
> +    REG_PC = 32
> +
> +    def test_aarch64_virt(self):
> +        """
> +        :avocado: tags=arch:aarch64
> +        :avocado: tags=machine:virt
> +        :avocado: tags=cpu:cortex-a53
> +        """
> +        kernel_url = ('https://archives.fedoraproject.org/pub/archive/fedora'
> +                      '/linux/releases/29/Everything/aarch64/os/images/pxeboot'
> +                      '/vmlinuz')
> +        kernel_hash = '8c73e469fc6ea06a58dc83a628fc695b693b8493'
> +        kernel_path = self.fetch_asset(kernel_url, asset_hash=kernel_hash)
> +
> +        self.reverse_debugging(
> +            args=('-kernel', kernel_path, '-cpu', 'cortex-a53'))

Quibbles aside it's excellent to have a test that exercises the
functionality.