Ben Gamari pushed to branch wip/loop-backtrace at Glasgow Haskell Compiler / GHC Commits: b709d077 by Ben Gamari at 2026-06-21T17:01:08-04:00 Throw nontermination exceptions via `throw` This ensures that the exception that results gets the usual backtrace annotations. This is a first step to #21878. - - - - - 9 changed files: - + changelog.d/builtin-exception-backtraces - libraries/ghc-internal/include/RtsIfaceSymbols.h - libraries/ghc-internal/src/GHC/Internal/Control/Exception/Base.hs - rts/Prelude.h - rts/RtsStartup.c - rts/Schedule.c - rts/include/rts/RtsToHsIface.h - testsuite/tests/rts/LoopBacktrace.stderr - testsuite/tests/rts/T2783.stderr Changes: ===================================== changelog.d/builtin-exception-backtraces ===================================== @@ -0,0 +1,10 @@ +section: rts +synopsis: Non-termination exceptions now have backtrace annotations +issues: #21878 +mrs: !16158 +description: { + The `NonTermination` exception (manifesting in printed exception output as + `<<loop>>`) now include `Backtrace` `ExceptionAnnotations`, like exceptions + thrown from user-written Haskell. +} + ===================================== libraries/ghc-internal/include/RtsIfaceSymbols.h ===================================== @@ -20,7 +20,7 @@ CLOSURE(GHCziInternalziIOziException, blockedIndefinitelyOnSTM_closure) CLOSURE(GHCziInternalziIOziException, cannotCompactFunction_closure) CLOSURE(GHCziInternalziIOziException, cannotCompactPinned_closure) CLOSURE(GHCziInternalziIOziException, cannotCompactMutable_closure) -CLOSURE(GHCziInternalziControlziExceptionziBase, nonTermination_closure) +CLOSURE(GHCziInternalziControlziExceptionziBase, nonTerminationError_closure) CLOSURE(GHCziInternalziControlziExceptionziBase, nestedAtomically_closure) CLOSURE(GHCziInternalziControlziExceptionziBase, noMatchingContinuationPrompt_closure) #if defined(mingw32_HOST_OS) ===================================== libraries/ghc-internal/src/GHC/Internal/Control/Exception/Base.hs ===================================== @@ -108,7 +108,9 @@ module GHC.Internal.Control.Exception.Base ( impossibleError, impossibleConstraintError, nonExhaustiveGuardsError, patError, noMethodBindingError, typeError, - nonTermination, nestedAtomically, noMatchingContinuationPrompt, + nonTermination, nonTerminationError, + nestedAtomically, + noMatchingContinuationPrompt, ) where import GHC.Internal.Base ( @@ -448,6 +450,9 @@ impossibleConstraintError s = errorWithoutStackTrace (unpackCStringUtf8# s) -- GHC's RTS calls this +nonTerminationError :: IO () +nonTerminationError = throwIO NonTermination + nonTermination :: SomeException nonTermination = toException NonTermination ===================================== rts/Prelude.h ===================================== @@ -58,7 +58,7 @@ extern StgClosure ZCMain_main_closure; #define cannotCompactFunction_closure ghc_hs_iface->cannotCompactFunction_closure #define cannotCompactPinned_closure ghc_hs_iface->cannotCompactPinned_closure #define cannotCompactMutable_closure ghc_hs_iface->cannotCompactMutable_closure -#define nonTermination_closure ghc_hs_iface->nonTermination_closure +#define nonTerminationError_closure ghc_hs_iface->nonTerminationError_closure #define nestedAtomically_closure ghc_hs_iface->nestedAtomically_closure #define absentSumFieldError_closure ghc_hs_iface->absentSumFieldError_closure #define underflowException_closure ghc_hs_iface->underflowException_closure ===================================== rts/RtsStartup.c ===================================== @@ -193,7 +193,7 @@ static void initBuiltinGcRoots(void) getStablePtr((StgPtr)heapOverflow_closure); getStablePtr((StgPtr)unpackCString_closure); getStablePtr((StgPtr)blockedIndefinitelyOnMVar_closure); - getStablePtr((StgPtr)nonTermination_closure); + getStablePtr((StgPtr)nonTerminationError_closure); getStablePtr((StgPtr)blockedIndefinitelyOnSTM_closure); getStablePtr((StgPtr)allocationLimitExceeded_closure); getStablePtr((StgPtr)cannotCompactFunction_closure); ===================================== rts/Schedule.c ===================================== @@ -3276,6 +3276,17 @@ findAtomicallyFrameHelper (Capability *cap, StgTSO *tso) } } +static void throwNontermination(Capability *cap, StgTSO *tso) { + StgStack *stack = tso->stackobj; + stack->sp -= 3; + stack->sp[0] = (W_)&stg_enter_info; + stack->sp[1] = (W_)nonTerminationError_closure; + stack->sp[2] = (W_)&stg_ap_v_info; + tso->why_blocked = NotBlocked; + appendToRunQueue(cap,tso); +} + + /* ----------------------------------------------------------------------------- resurrectThreads is called after garbage collection on the list of threads found to be garbage. Each of these threads will be woken @@ -3313,8 +3324,7 @@ resurrectThreads (StgTSO *threads) (StgClosure *)blockedIndefinitelyOnMVar_closure); break; case BlockedOnBlackHole: - throwToSingleThreaded(cap, tso, - (StgClosure *)nonTermination_closure); + throwNontermination(cap, tso); break; case BlockedOnSTM: throwToSingleThreaded(cap, tso, ===================================== rts/include/rts/RtsToHsIface.h ===================================== @@ -25,7 +25,7 @@ typedef struct { StgClosure *cannotCompactFunction_closure; // GHC.Internal.IO.Exception.cannotCompactFunction_closure StgClosure *cannotCompactPinned_closure; // GHC.Internal.IO.Exception.cannotCompactPinned_closure StgClosure *cannotCompactMutable_closure; // GHC.Internal.IO.Exception.cannotCompactMutable_closure - StgClosure *nonTermination_closure; // GHC.Internal.Control.Exception.Base.nonTermination_closure + StgClosure *nonTerminationError_closure; // GHC.Internal.Control.Exception.Base.nonTerminationError_closure StgClosure *nestedAtomically_closure; // GHC.Internal.Control.Exception.Base.nestedAtomically_closure StgClosure *noMatchingContinuationPrompt_closure; // GHC.Internal.Control.Exception.Base.noMatchingContinuationPrompt_closure StgClosure *blockedOnBadFD_closure; // GHC.Internal.Event.Thread.blockedOnBadFD_closure ===================================== testsuite/tests/rts/LoopBacktrace.stderr ===================================== @@ -3,19 +3,19 @@ LoopBacktrace: Uncaught exception ghc-internal:GHC.Internal.Control.Exception.Ba <<loop>> IPE backtrace: - Cmm$rts/StgStartup.cmm. (:) - Cmm$rts/Exception.cmm. (:) - GHC.Internal.Base.thenIO (libraries/ghc-internal/src/GHC/Internal/Base.hs:2336:1-72) - GHC.Internal.IO.Handle.Text. (:) - GHC.Internal.Show. (:) - Main.x (LoopBacktrace.hs:6:1-9) - Cmm$rts/Updates.cmm. (:) - GHC.Num.Integer. (:) - Cmm$rts/HeapStackCheck.cmm. (:) - GHC.Internal.IO.throwIO (libraries/ghc-internal/src/GHC/Internal/IO.hs:285:36) - GHC.Internal.Exception.bindIO (libraries/ghc-internal/src/GHC/Internal/Base.hs:2333:1-76) - GHC.Internal.Exception.Backtrace.bindIO (libraries/ghc-internal/src/GHC/Internal/Base.hs:2333:1-76) - GHC.Internal.Exception.Backtrace.$ (libraries/ghc-internal/src/GHC/Internal/Base.hs:2267:1-9) + GHC.Internal.Exception.Backtrace.collectBacktraces' (libraries/ghc-internal/src/GHC/Internal/Exception/Backtrace.hs:(179,1)-(202,25)) + GHC.Internal.Exception.Backtrace.collectBacktraces (libraries/ghc-internal/src/GHC/Internal/Exception/Backtrace.hs:174:39-56) + GHC.Internal.Exception.toExceptionWithBacktrace (libraries/ghc-internal/src/GHC/Internal/Exception.hs:(179,26)-(181,53)) + GHC.Internal.IO.throwIO (libraries/ghc-internal/src/GHC/Internal/IO.hs:293:36) + Cmm$rts/HeapStackCheck.cmm. (:) + GHC.Internal.Bignum.Integer.integerAdd (libraries/ghc-internal/src/GHC/Internal/Bignum/Integer.hs:(547,1)-(571,52)) + Cmm$rts/Updates.cmm. (:) + Main.x (LoopBacktrace.hs:6:1-9) + GHC.Internal.Show.show (libraries/ghc-internal/src/GHC/Internal/Show.hs:497:10-21) + GHC.Internal.IO.Handle.Text.hPutStr' (libraries/ghc-internal/src/GHC/Internal/IO/Handle/Text.hs:667:29-37) + GHC.Internal.Base.thenIO (libraries/ghc-internal/src/GHC/Internal/Base.hs:2337:1-72) + Cmm$rts/Exception.cmm. (:) + Cmm$rts/StgStartup.cmm. (:) HasCallStack backtrace: - throwIO, called at libraries/ghc-internal/src/GHC/Internal/Control/Exception/Base.hs:446:23 in ghc-internal:GHC.Internal.Control.Exception.Base + throwIO, called at libraries/ghc-internal/src/GHC/Internal/Control/Exception/Base.hs:452:23 in ghc-internal:GHC.Internal.Control.Exception.Base ===================================== testsuite/tests/rts/T2783.stderr ===================================== @@ -1,3 +1,7 @@ T2783: Uncaught exception ghc-internal:GHC.Internal.Control.Exception.Base.NonTermination: <<loop>> + +HasCallStack backtrace: + throwIO, called at libraries/ghc-internal/src/GHC/Internal/Control/Exception/Base.hs:452:23 in ghc-internal:GHC.Internal.Control.Exception.Base + View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/b709d07758de0315cfa9022662305b67... -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/b709d07758de0315cfa9022662305b67... You're receiving this email because of your account on gitlab.haskell.org.