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https://github.com/cirosantilli/linux-kernel-module-cheat.git
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qemu: allow turning -O0 debug build on or off, use -O0 by default
OMG, I was wasting time in ARM all along!!!
This commit is contained in:
Ciro Santilli 六四事件 法轮功
67
README.adoc
67
README.adoc
@@ -9786,25 +9786,27 @@ This is of course trivial since they are just regular userland programs on the h
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./run --debug-vm
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....
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Then you could:
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....
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break edu_mmio_read
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run
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....
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And in QEMU:
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....
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./qemu_edu.sh
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....
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Or for a faster development loop:
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....
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./run --debug-vm-args '-ex "break edu_mmio_read" -ex "run"'
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./run --debug-vm-args '-ex "break qemu_add_opts" -ex "run"'
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....
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Our default emulator builds are optimized with `gcc -O2 -g`. To use `-O0` instead, build and run with:
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....
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./build-qemu --qemu-build-type debug --verbose
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./run --debug-vm
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./build-gem5 --gem5-build-type debug --verbose
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./run --debug-vm --emulator-gem5
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....
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The `--verbose` is optional, but shows clearly each GCC build command so that you can confirm what `--*-build-type` is doing.
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The build outputs are automatically stored in a different directories for optimized and debug builds, which prevents `debug` files from overwriting `opt` ones. Therefore, `--gem5-build-id` is not required:
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The price to pay for debuggability is high however: a Linux kernel boot was about 3x slower in QEMU and 14 times slower in gem5 debug compared to opt, see benchmarks at: xref:benchmark-linux-kernel-boot[xrefstyle=full]
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When in <<qemu-text-mode>>, using `--debug-vm` makes Ctrl-C not get passed to the QEMU guest anymore: it is instead captured by GDB itself, so allow breaking. So e.g. you won't be able to easily quit from a guest program like:
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....
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@@ -9828,19 +9830,28 @@ echo 'kernel.perf_event_paranoid=1' | sudo tee -a /etc/sysctl.conf
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sudo sysctl -p
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....
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Then use it as:
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Then use it with your content of interest, for example:
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....
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./run --debug-vm-rr
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./run --debug-vm-rr --userland userland/c/hello.c
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....
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Once you are left in the RR GDB shell, just continue:
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This will first run the program once until completion, and then restart the program at the very first instruction at `_start` and leave you in a GDB shell.
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From there, run the program until your point of interest, e.g.:
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....
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break qemu_add_opts
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continue
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....
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you can now reiably use reverse debugging commands such as `reverse-continue` and `reverse-next`!
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and you can now reiably use reverse debugging commands such as `reverse-continue`, `reverse-finish` and `reverse-next`!
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To restart debugging again after quitting `rr`, simlpy run on your host terminal:
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....
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rr replay
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....
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==== Debug gem5 Python scripts
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@@ -12158,25 +12169,7 @@ In order to use different build options, you might also want to use <<gem5-build
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==== gem5 debug build
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The `gem5.debug` executable has optimizations turned off unlike the default `gem5.opt`, and provides a much better <<debug-the-emulator,debug experience>>:
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....
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./build-gem5 --arch aarch64 --gem5-build-type debug
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./run --arch aarch64 --debug-vm --emulator gem5 --gem5-build-type debug
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....
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The build outputs are automatically stored in a different directory from other build types such as `.opt` build, which prevents `.debug` files from overwriting `.opt` ones.
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Therefore, `--gem5-build-id` is not required.
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The price to pay for debuggability is high however: a Linux kernel boot was about 14 times slower than opt at 71e927e63bda6507d5a528f22c78d65099bdf36f between the commands:
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....
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./run --arch aarch64 --eval 'm5 exit' --emulator gem5 --linux-build-id v4.16
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./run --arch aarch64 --eval 'm5 exit' --emulator gem5 --linux-build-id v4.16 --gem5-build-type debug
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....
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so you will likely only use this when it is unavoidable. This is also benchmarked at: xref:benchmark-linux-kernel-boot[xrefstyle=full]
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Explained at: xref:debug-the-emulator[xrefstyle=full].
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==== gem5 clang build
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@@ -26,14 +26,19 @@ class Main(common.BuildCliFunction):
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target_list = '{}-linux-user'.format(self.env['arch'])
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else:
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target_list = '{}-softmmu'.format(self.env['arch'])
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if self.env['qemu_build_type'] == 'debug':
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# https://stackoverflow.com/questions/4689136/debug-qemu-with-gdb
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build_type_cmd = ['--enable-debug', LF]
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else:
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build_type_cmd = []
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self.sh.run_cmd(
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[
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os.path.join(self.env['qemu_source_dir'], 'configure'), LF,
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'--enable-debug', LF,
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'--enable-trace-backends=simple', LF,
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'--target-list={}'.format(target_list), LF,
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'--enable-sdl', LF,
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] +
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build_type_cmd +
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self.sh.add_newlines(self.env['extra_config_args']),
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extra_paths=[self.env['ccache_dir']],
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cwd=build_dir
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24
common.py
24
common.py
@@ -144,6 +144,13 @@ for key in consts['emulator_short_to_long_dict']:
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consts['emulator_choices'].add(consts['emulator_short_to_long_dict'][key])
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consts['host_arch'] = platform.processor()
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consts['guest_lkmc_home'] = os.sep + consts['repo_short_id']
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consts['build_type_choices'] = [
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# -O2 -g
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'opt',
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# -O0 -g
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'debug'
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]
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consts['build_type_default'] = 'opt'
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class ExitLoop(Exception):
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pass
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@@ -325,7 +332,8 @@ Default: {}
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)
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self.add_argument(
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'--gem5-build-type',
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default='opt',
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choices=consts['build_type_choices'],
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default=consts['build_type_default'],
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help='gem5 build type, most often used for "debug" builds.'
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)
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self.add_argument(
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@@ -441,11 +449,16 @@ Use the docker download Ubuntu root filesystem instead of the default Buildroot
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# QEMU.
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self.add_argument(
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'-Q',
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'--qemu-build-id',
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default=consts['default_build_id'],
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help='QEMU build ID. Allows you to keep multiple separate QEMU builds.'
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)
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self.add_argument(
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'--qemu-build-type',
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choices=consts['build_type_choices'],
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default=consts['build_type_default'],
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help='QEMU build type, most often used for "debug" vs optimized builds.'
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)
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self.add_argument(
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'--qemu-which',
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choices=[consts['repo_short_id'], 'host'],
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@@ -743,7 +756,12 @@ Incompatible archs are skipped.
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env['linux_buildroot_build_dir'] = join(env['buildroot_build_build_dir'], 'linux-custom')
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# QEMU
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env['qemu_build_dir'] = join(env['out_dir'], 'qemu', env['qemu_build_id'])
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env['qemu_build_dir'] = join(
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env['out_dir'],
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'qemu',
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env['qemu_build_id'],
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env['qemu_build_type']
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)
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env['qemu_img_basename'] = 'qemu-img'
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env['qemu_img_executable'] = join(env['qemu_build_dir'], env['qemu_img_basename'])
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if env['userland'] is None:
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