Rodrigo Mesquita pushed to branch wip/romes/step-out-5 at Glasgow Haskell Compiler / GHC Commits: 20668d60 by Rodrigo Mesquita at 2025-06-19T13:12:21+01:00 debugger: Implement step-out feature Implements support for stepping-out of a function (aka breaking right after returning from a function) in the interactive debugger. It also introduces a GHCi command :stepout to step-out of a function being debugged in the interpreter. The feature is described as: Stop at the first breakpoint immediately after returning from the current function scope. Known limitations: because a function tail-call does not push a stack frame, if step-out is used inside of a function that was tail-called, execution will not be returned to its caller, but rather its caller's first non-tail caller. On the other hand, it means the debugger follows the more realistic execution of the program. In the following example: .. code-block:: none f = do a b <--- (1) set breakpoint then step in here c b = do ... d <--- (2) step-into this tail call d = do ... something <--- (3) step-out here ... Stepping-out will stop execution at the `c` invokation in `f`, rather than stopping at `b`. The key idea is simple: When step-out is enabled, traverse the runtime stack until a continuation BCO is found -- and enable the breakpoint heading that BCO explicitly using its tick-index. The details are specified in `Note [Debugger: Step-out]` in `rts/Interpreter.c`. Since PUSH_ALTS BCOs (representing case continuations) were never headed by a breakpoint (unlike the case alternatives they push), we introduced the BRK_ALTS instruction to allow the debugger to set a case continuation to stop at the breakpoint heading the alternative that is taken. This is further described in `Note [Debugger: BRK_ALTS]`. Fixes #26042 - - - - - 8f0a3a46 by Rodrigo Mesquita at 2025-06-19T13:12:21+01:00 debugger: Filter step-out stops by SrcSpan To implement step-out, the RTS looks for the first continuation frame on the stack and explicitly enables its entry breakpoint. However, some continuations will be contained in the function from which step-out was initiated (trivial example is a case expression). Similarly to steplocal, we will filter the breakpoints at which the RTS yields to the debugger based on the SrcSpan. When doing step-out, only stop if the breakpoint is /not/ contained in the function from which we initiated it. This is especially relevant in monadic statements such as IO which is compiled to a long chain of case expressions. See Note [Debugger: Filtering step-out stops] - - - - - 44 changed files: - compiler/GHC/ByteCode/Asm.hs - compiler/GHC/ByteCode/Instr.hs - compiler/GHC/Driver/Config.hs - compiler/GHC/Runtime/Eval.hs - compiler/GHC/Runtime/Eval/Types.hs - compiler/GHC/StgToByteCode.hs - docs/users_guide/ghci.rst - ghc/GHCi/UI.hs - libraries/ghc-heap/GHC/Exts/Heap/Closures.hs - libraries/ghc-heap/GHC/Exts/Heap/FFIClosures_ProfilingDisabled.hsc - libraries/ghc-heap/GHC/Exts/Heap/FFIClosures_ProfilingEnabled.hsc - libraries/ghc-heap/tests/parse_tso_flags.hs - libraries/ghci/GHCi/Debugger.hs - libraries/ghci/GHCi/Message.hs - libraries/ghci/GHCi/Run.hs - rts/Disassembler.c - rts/Interpreter.c - rts/Interpreter.h - rts/RtsSymbols.c - rts/StgMiscClosures.cmm - rts/include/rts/Bytecodes.h - rts/include/rts/Constants.h - rts/include/rts/storage/Closures.h - + testsuite/tests/ghci.debugger/scripts/T26042b.hs - + testsuite/tests/ghci.debugger/scripts/T26042b.script - + testsuite/tests/ghci.debugger/scripts/T26042b.stdout - + testsuite/tests/ghci.debugger/scripts/T26042c.hs - + testsuite/tests/ghci.debugger/scripts/T26042c.script - + testsuite/tests/ghci.debugger/scripts/T26042c.stdout - + testsuite/tests/ghci.debugger/scripts/T26042d.hs - + testsuite/tests/ghci.debugger/scripts/T26042d.script - + testsuite/tests/ghci.debugger/scripts/T26042d.stdout - + testsuite/tests/ghci.debugger/scripts/T26042e.hs - + testsuite/tests/ghci.debugger/scripts/T26042e.script - + testsuite/tests/ghci.debugger/scripts/T26042e.stdout - + testsuite/tests/ghci.debugger/scripts/T26042f.hs - + testsuite/tests/ghci.debugger/scripts/T26042f.script - + testsuite/tests/ghci.debugger/scripts/T26042f1.stderr - + testsuite/tests/ghci.debugger/scripts/T26042f1.stdout - + testsuite/tests/ghci.debugger/scripts/T26042f2.stdout - + testsuite/tests/ghci.debugger/scripts/T26042g.hs - + testsuite/tests/ghci.debugger/scripts/T26042g.script - + testsuite/tests/ghci.debugger/scripts/T26042g.stdout - testsuite/tests/ghci.debugger/scripts/all.T The diff was not included because it is too large. View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/5df3c3fcec5b08ce8bd90ebed02be5d... -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/5df3c3fcec5b08ce8bd90ebed02be5d... You're receiving this email because of your account on gitlab.haskell.org.