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[debugger] Work around a debugger issue when using the interpreter #15451

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Merged
rolfbjarne merged 9 commits into from
Jul 15, 2022
Merged

[debugger] Work around a debugger issue when using the interpreter #15451

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d05066a
fix debugger
thaystg Jul 11, 2022
359ec53
Merge branch 'main' into thays_debug_workaround
thaystg Jul 11, 2022
610c6f2
Merge branch 'main' into thays_debug_workaround
mandel-macaque Jul 11, 2022
86ceac3
Hide output, add comment
rolfbjarne Jul 12, 2022
88a834b
We only need the workaround for .NET.
rolfbjarne Jul 12, 2022
7bd541b
Keep calling mono_debug_init if workaround is not in effect.
rolfbjarne Jul 12, 2022
2f8e7c6
Add an escape hatch.
rolfbjarne Jul 13, 2022
9b78d77
NULL-terminate the argc array.
rolfbjarne Jul 13, 2022
718494f
Add a dummy argument.
rolfbjarne Jul 14, 2022
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14 changes: 10 additions & 4 deletions runtime/monovm-bridge.m
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Original file line number Diff line number Diff line change
Expand Up @@ -69,9 +69,6 @@
DEBUG_LAUNCH_TIME_PRINT ("\tDebug init time");
#endif

if (xamarin_init_mono_debug)
mono_debug_init (MONO_DEBUG_FORMAT_MONO);

mono_install_assembly_preload_hook (xamarin_assembly_preload_hook, NULL);
mono_install_load_aot_data_hook (xamarin_load_aot_data, xamarin_free_aot_data, NULL);

Expand All @@ -85,7 +82,16 @@
mono_install_unhandled_exception_hook (xamarin_unhandled_exception_handler, NULL);
mono_install_ftnptr_eh_callback (xamarin_ftnptr_exception_handler);

mono_jit_init_version ("MonoTouch", "mobile");
const char *argc[] = {
"",
"--interp=-all"
};

if (xamarin_init_mono_debug)
mono_main (2, (char**)argc);

@rolfbjarne rolfbjarne Jul 11, 2022

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Could you explain runtime-wise why this works around the problem?

@thaystg thaystg Jul 11, 2022

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Yes, sure.
The issue on runtime side was that we are initializing interpreter before setting the debugger attributes. So when we execute this code: https://github.com/dotnet/runtime/blob/5529dc79e9f35d70e9d01318d31844984b860dd4/src/mono/mono/mini/interp/interp.c#L8121
mdb_optimizations was false, then we keep the default optimizations of the interpreter which was breaking the debugger experience.
In this workaround I'm passing --interp=-all in the parameters, so I'm disabling the interpreter optimizations and the debugger works well.

@rolfbjarne rolfbjarne Jul 11, 2022

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Is this only a problem in .NET 6? Or legacy mono as well? (i.e. mono/mono's 2020-02 branch)

@thaystg thaystg Jul 11, 2022 •
edited
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I'm almost sure that it's a problem only on .net 6, but I would ask someone to test to double check. It's really easy to reproduce:

public static void MethodMyMethod()
{
      var e2 = new Exception("hi thays");
      var e1 = e2;
      if (e1.Equals(e2))
	      Console.WriteLine("equals");
}

Adding a breakpoint on if statement and looking at locals, with the optimizations turned on we only see the content of variable e2, e1 is null.

@samhouts samhouts Jul 12, 2022

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Is this going to have implications for hot reload on .NET MAUI?

@thaystg thaystg Jul 12, 2022

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I don't think so. @lambdageek do you have any thoughts about this workaround?

else
mono_jit_init_version ("MonoTouch", "mobile");
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thaystg marked this conversation as resolved.

/*
As part of mono initialization a preload hook is added that overrides ours, so we need to re-instate it here.
This is wasteful, but there's no way to manipulate the preload hook list except by adding to it.
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