[clr-interp] Support for breakpoints and stepping

[matouskozak]

Summary

This PR adds debugger support for the CoreCLR interpreter, enabling IDE breakpoints and single-stepping functionality.

Key Changes

Breakpoint Support:

• Enable breakpoints in interpreter via INTOP_BREAKPOINT opcode injection
• Add IL offset 0 → IR offset 0 mapping for method entry breakpoints
• Refactor ApplyPatch/UnapplyPatch for interpreter code patches
• Add activation flag for interpreter patches (needed because opcode 0 is valid INTOP_RET)

Single-Stepping Support:

• Add InterpreterStepHelper class to encapsulate step setup logic
• Per-thread context bypass address/opcode fields for resuming past breakpoints
• Implement TrapInterpreterCodeStep for step-in/step-over/step-out
• Call OnMethodEnter from INTOP_DEBUG_METHOD_ENTER to notify debugger of method entry (needed for indirect calls)

Interpreter Compiler Changes:

• Add INTOP_DEBUG_SEQ_POINT for placing breakpoints at { as NOPs get collapsed.

Testing

• Verified IDE breakpoints work with interpreted code
• Single-stepping (step-in, step-over, step-out) functional
• No regressions to existing debugger support verified locally using diagnostictests

Notes/TODOs

• Stack walking workaround needs to be reverted once proper fix is in place
• m_interpActivated should be generalized to all patches (stop using opcode == 0 as "not active") [debugger] Replace PRDIsEmpty(opcode) activation check with explicit m_activated flag #124499
• s_interpOpLen / opcode name tables in executioncontrol.cpp are debug logging aids — TODO remove
• Long-term plan: Extract JIT-specific code into HardwareExecutionControl derived class, create InterpreterExecutionControl for interpreter support

---

[Copilot]

Pull request overview

This work-in-progress pull request adds support for managed debugger breakpoints in the CoreCLR interpreter. The changes extend the existing user breakpoint support (e.g., Debugger.Break()) to support IDE breakpoints and enable setting breakpoints when the program is stopped.

Changes:

• Adds interpreter single-step thread state flag and supporting methods
• Introduces new INTOP_SINGLESTEP opcode for step-over operations
• Implements InterpreterWalker to analyze interpreter bytecode for debugger stepping
• Modifies breakpoint execution logic to distinguish between IDE breakpoints and step-out breakpoints
• Enables JIT completion notifications for interpreter code
• Pre-inserts IL offset 0 entry in the IL-to-native map to support method entry breakpoints

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 11 comments.

Show a summary per file

File	Description
src/coreclr/vm/threads.h	Adds TSNC_InterpreterSingleStep thread state flag and related methods
src/coreclr/vm/jitinterface.cpp	Removes interpreter code exclusion from JITComplete notifications
src/coreclr/vm/interpexec.cpp	Implements breakpoint and single-step handling with opcode replacement
src/coreclr/vm/codeman.h	Adds IsInterpretedCode() helper method
src/coreclr/interpreter/intops.h	Adds helper functions to classify interpreter opcodes
src/coreclr/interpreter/inc/intops.def	Defines INTOP_SINGLESTEP opcode
src/coreclr/interpreter/compiler.cpp	Pre-inserts IL offset 0 mapping for method entry breakpoints
src/coreclr/debug/ee/interpreterwalker.h	Declares InterpreterWalker class for bytecode analysis
src/coreclr/debug/ee/interpreterwalker.cpp	Implements bytecode walker for debugger stepping operations
src/coreclr/debug/ee/functioninfo.cpp	Uses GetInterpreterCodeFromInterpreterPrecodeIfPresent for code address
src/coreclr/debug/ee/executioncontrol.h	Defines BreakpointInfo structure and GetBreakpointInfo method
src/coreclr/debug/ee/executioncontrol.cpp	Implements INTOP_SINGLESTEP patch support and breakpoint info retrieval
src/coreclr/debug/ee/controller.h	Includes interpreterwalker.h header
src/coreclr/debug/ee/controller.cpp	Implements TrapStep for interpreter using InterpreterWalker
src/coreclr/debug/ee/CMakeLists.txt	Adds interpreterwalker source files to build

[Copilot]

Pull request overview

Copilot reviewed 19 out of 19 changed files in this pull request and generated 9 comments.

[Copilot]

Pull request overview

Copilot reviewed 21 out of 21 changed files in this pull request and generated 8 comments.

[Copilot]

Pull request overview

Copilot reviewed 22 out of 22 changed files in this pull request and generated 2 comments.

Comments suppressed due to low confidence (1)

src/coreclr/debug/ee/controller.h:569

• DebuggerControllerPatch::IsActivated relies on m_interpActivated for interpreter patches to avoid treating opcode==0 as “not active”. However, there are activation paths where a patch can become logically active without going through InterpreterExecutionControl::ApplyPatch (e.g., when another patch already exists at the same address and activation is skipped by copying the opcode). In those cases, if the original opcode is 0 (INTOP_RET), IsActivated will still return false, breaking the invariants that bound patches are activated. Ensure m_interpActivated is set/cleared consistently for all interpreter patch activation/deactivation paths, not just ApplyPatch/UnapplyPatch.

    bool IsActivated()
    {
#ifdef FEATURE_INTERPRETER
        // m_interpActivated is set only by InterpreterExecutionControl::ApplyPatch
        if (m_interpActivated)
        {
            _ASSERTE(address != NULL);
            return TRUE;
        }
#endif // FEATURE_INTERPRETER

        // Patch is activate if we've stored a non-zero opcode
        // Note: this might be a problem as opcode 0 may be a valid opcode (see issue 366221).
        if( PRDIsEmpty(opcode) ) {
            return FALSE;
        }

        // Patch is active, so it must also be bound
        _ASSERTE( address != NULL );
        return TRUE;
    }

[Copilot]

Pull request overview

Copilot reviewed 21 out of 21 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 21 out of 21 changed files in this pull request and generated 2 comments.

[janvorli]

LGTM, thank you!