diff options
| -rw-r--r-- | compiler/GHC/Core/Make.hs | 25 | ||||
| -rw-r--r-- | libraries/ghc-prim/GHC/Prim/Exception.hs | 3 | ||||
| -rw-r--r-- | rts/Prelude.h | 10 | ||||
| -rw-r--r-- | rts/RtsStartup.c | 6 |
4 files changed, 41 insertions, 3 deletions
diff --git a/compiler/GHC/Core/Make.hs b/compiler/GHC/Core/Make.hs index f002637556..9f9e92e9f8 100644 --- a/compiler/GHC/Core/Make.hs +++ b/compiler/GHC/Core/Make.hs @@ -824,7 +824,9 @@ tYPE_ERROR_ID = mkRuntimeErrorId typeErrorName -- argument would require allocating a thunk. -- -- 4. it can't be CAFFY because that would mean making some non-CAFFY --- definitions that use unboxed sums CAFFY in unarise. +-- definitions that use unboxed sums CAFFY in unarise. We work around +-- this by declaring the absentSumFieldError as non-CAFfy, as described +-- in Note [Wired-in exceptions are not CAFfy]. -- -- Getting this wrong causes hard-to-debug runtime issues, see #15038. -- @@ -858,6 +860,21 @@ tYPE_ERROR_ID = mkRuntimeErrorId typeErrorName -- error. That's why it is OK for it to be un-catchable. -- +-- Note [Wired-in exceptions are not CAFfy] +-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +-- mkExceptionId claims that all exceptions are not CAFfy, despite the fact +-- that their closures' code may in fact contain CAF references. We get away +-- with this lie because the RTS ensures that all exception closures are +-- considered live by the GC by creating StablePtrs during initialization. +-- The lie is necessary to avoid unduly growing SRTs as these exceptions are +-- sufficiently common to warrant special treatment. +-- +-- At some point we could consider removing this optimisation as it is quite +-- fragile, but we do want to be careful to avoid adding undue cost. Unboxed +-- sums in particular are intended to be used in performance-critical contexts. +-- +-- See #15038, #21141. + absentSumFieldErrorName = mkWiredInIdName gHC_PRIM_PANIC @@ -899,6 +916,9 @@ rAISE_UNDERFLOW_ID = mkExceptionId raiseUnderflowName rAISE_DIVZERO_ID = mkExceptionId raiseDivZeroName -- | Exception with type \"forall a. a\" +-- +-- Any exceptions added via this function needs to be added to +-- the RTS's initBuiltinGcRoots() function. mkExceptionId :: Name -> Id mkExceptionId name = mkVanillaGlobalWithInfo name @@ -906,7 +926,8 @@ mkExceptionId name (vanillaIdInfo `setStrictnessInfo` mkClosedStrictSig [] botDiv `setCprInfo` mkCprSig 0 botCpr `setArityInfo` 0 - `setCafInfo` NoCafRefs) -- #15038 + `setCafInfo` NoCafRefs) + -- See Note [Wired-in exceptions are not CAFfy] mkRuntimeErrorId :: Name -> Id -- Error function diff --git a/libraries/ghc-prim/GHC/Prim/Exception.hs b/libraries/ghc-prim/GHC/Prim/Exception.hs index 592d597f44..0b9e9c165c 100644 --- a/libraries/ghc-prim/GHC/Prim/Exception.hs +++ b/libraries/ghc-prim/GHC/Prim/Exception.hs @@ -20,13 +20,14 @@ default () -- Double and Integer aren't available yet -- Note [Arithmetic exceptions] -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ --- -- ghc-prim provides several functions to raise arithmetic exceptions -- (raiseDivZero, raiseUnderflow, raiseOverflow) that are wired-in the RTS. -- These exceptions are meant to be used by the package implementing arbitrary -- precision numbers (Natural,Integer). It can't depend on `base` package to -- raise exceptions in a normal way because it would create a dependency -- cycle (base <-> bignum package). See #14664 +-- +-- See also: Note [Wired-in exceptions are not CAFfy] in GHC.Core.Make. foreign import prim "stg_raiseOverflowzh" raiseOverflow# :: State# RealWorld -> (# State# RealWorld, (# #) #) foreign import prim "stg_raiseUnderflowzh" raiseUnderflow# :: State# RealWorld -> (# State# RealWorld, (# #) #) diff --git a/rts/Prelude.h b/rts/Prelude.h index d2511b2fc3..5f1e070e33 100644 --- a/rts/Prelude.h +++ b/rts/Prelude.h @@ -19,6 +19,12 @@ #define PRELUDE_CLOSURE(i) extern StgClosure DLL_IMPORT_DATA_VARNAME(i) #endif +/* See Note [Wired-in exceptions are not CAFfy] in GHC.Core.Make. */ +PRELUDE_CLOSURE(ghczmprim_GHCziPrimziPanic_absentSumFieldError_closure); +PRELUDE_CLOSURE(ghczmprim_GHCziPrimziException_raiseUnderflow_closure); +PRELUDE_CLOSURE(ghczmprim_GHCziPrimziException_raiseOverflow_closure); +PRELUDE_CLOSURE(ghczmprim_GHCziPrimziException_raiseDivZZero_closure); + /* Define canonical names so we can abstract away from the actual * modules these names are defined in. */ @@ -111,6 +117,10 @@ PRELUDE_INFO(base_GHCziStable_StablePtr_con_info); #define nonTermination_closure DLL_IMPORT_DATA_REF(base_ControlziExceptionziBase_nonTermination_closure) #define nestedAtomically_closure DLL_IMPORT_DATA_REF(base_ControlziExceptionziBase_nestedAtomically_closure) #define doubleReadException DLL_IMPORT_DATA_REF(base_GHCziIOPort_doubleReadException_closure) +#define absentSumFieldError_closure DLL_IMPORT_DATA_REF(ghczmprim_GHCziPrimziPanic_absentSumFieldError_closure) +#define raiseUnderflowException_closure DLL_IMPORT_DATA_REF(ghczmprim_GHCziPrimziException_raiseUnderflow_closure) +#define raiseOverflowException_closure DLL_IMPORT_DATA_REF(ghczmprim_GHCziPrimziException_raiseOverflow_closure) +#define raiseDivZeroException_closure DLL_IMPORT_DATA_REF(ghczmprim_GHCziPrimziException_raiseDivZZero_closure) #define blockedOnBadFD_closure DLL_IMPORT_DATA_REF(base_GHCziEventziThread_blockedOnBadFD_closure) diff --git a/rts/RtsStartup.c b/rts/RtsStartup.c index d64f87cf7e..649489d1e3 100644 --- a/rts/RtsStartup.c +++ b/rts/RtsStartup.c @@ -213,6 +213,12 @@ static void initBuiltinGcRoots(void) #else getStablePtr((StgPtr)processRemoteCompletion_closure); #endif + + /* See Note [Wired-in exceptions are not CAFfy] in GHC.Core.Make. */ + getStablePtr((StgPtr)absentSumFieldError_closure); + getStablePtr((StgPtr)raiseUnderflowException_closure); + getStablePtr((StgPtr)raiseOverflowException_closure); + getStablePtr((StgPtr)raiseDivZeroException_closure); } void |