/* ----------------------------------------------------------------------------- * * (c) The GHC Team, 1998-2004 * * Exception support * * This file is written in a subset of C--, extended with various * features specific to GHC. It is compiled by GHC directly. For the * syntax of .cmm files, see the parser in ghc/compiler/cmm/CmmParse.y. * * ---------------------------------------------------------------------------*/ #include "Cmm.h" #include "RaiseAsync.h" import CLOSURE ghczmprim_GHCziTypes_True_closure; /* ----------------------------------------------------------------------------- Exception Primitives A thread can request that asynchronous exceptions not be delivered ("masked") for the duration of an I/O computation. The primitives maskAsyncExceptions# :: IO a -> IO a and maskUninterruptible# :: IO a -> IO a are used for this purpose. During a masked section, asynchronous exceptions may be unmasked again temporarily: unmaskAsyncExceptions# :: IO a -> IO a Furthermore, asynchronous exceptions are masked automatically during the execution of an exception handler. All three of these primitives leave a continuation on the stack which reverts to the previous state (masked interruptible, masked non-interruptible, or unmasked) on exit. A thread which wants to raise an exception in another thread (using killThread#) must block until the target thread is ready to receive it. The action of unmasking exceptions in a thread will release all the threads waiting to deliver exceptions to that thread. NB. there's a bug in here. If a thread is inside an unsafePerformIO, and inside maskAsyncExceptions# (there is an unmaskAsyncExceptions_ret on the stack), and it is blocked in an interruptible operation, and it receives an exception, then the unsafePerformIO thunk will be updated with a stack object containing the unmaskAsyncExceptions_ret frame. Later, when someone else evaluates this thunk, the original masking state is not restored. -------------------------------------------------------------------------- */ INFO_TABLE_RET(stg_unmaskAsyncExceptionszh_ret, RET_SMALL, W_ info_ptr) /* explicit stack */ { unwind Sp = Sp + WDS(1); CInt r; P_ ret; ret = R1; StgTSO_flags(CurrentTSO) = %lobits32( TO_W_(StgTSO_flags(CurrentTSO)) & ~(TSO_BLOCKEX|TSO_INTERRUPTIBLE)); /* Eagerly raise a masked exception, if there is one */ if (StgTSO_blocked_exceptions(CurrentTSO) != END_TSO_QUEUE) { STK_CHK_P_LL (WDS(2), stg_unmaskAsyncExceptionszh_ret_info, R1); /* * We have to be very careful here, as in killThread#, since * we are about to raise an async exception in the current * thread, which might result in the thread being killed. */ Sp_adj(-2); Sp(1) = ret; Sp(0) = stg_ret_p_info; SAVE_THREAD_STATE(); (r) = ccall maybePerformBlockedException (MyCapability() "ptr", CurrentTSO "ptr"); if (r != 0::CInt) { if (StgTSO_what_next(CurrentTSO) == ThreadKilled::I16) { jump stg_threadFinished []; } else { LOAD_THREAD_STATE(); ASSERT(StgTSO_what_next(CurrentTSO) == ThreadRunGHC::I16); R1 = ret; jump %ENTRY_CODE(Sp(0)) [R1]; } } else { /* the thread might have been removed from the blocked_exception list by someone else in the meantime. Just restore the stack pointer and continue. */ Sp_adj(2); } } Sp_adj(1); R1 = ret; jump %ENTRY_CODE(Sp(0)) [R1]; } INFO_TABLE_RET(stg_maskAsyncExceptionszh_ret, RET_SMALL, W_ info_ptr) return (P_ ret) { StgTSO_flags(CurrentTSO) = %lobits32( TO_W_(StgTSO_flags(CurrentTSO)) | TSO_BLOCKEX | TSO_INTERRUPTIBLE ); return (ret); } INFO_TABLE_RET(stg_maskUninterruptiblezh_ret, RET_SMALL, W_ info_ptr) return (P_ ret) { StgTSO_flags(CurrentTSO) = %lobits32( (TO_W_(StgTSO_flags(CurrentTSO)) | TSO_BLOCKEX) & ~TSO_INTERRUPTIBLE ); return (ret); } stg_maskAsyncExceptionszh /* explicit stack */ { /* Args: R1 :: IO a */ STK_CHK_P_LL (WDS(1)/* worst case */, stg_maskAsyncExceptionszh, R1); if ((TO_W_(StgTSO_flags(CurrentTSO)) & TSO_BLOCKEX) == 0) { /* avoid growing the stack unnecessarily */ if (Sp(0) == stg_maskAsyncExceptionszh_ret_info) { Sp_adj(1); } else { Sp_adj(-1); Sp(0) = stg_unmaskAsyncExceptionszh_ret_info; } } else { if ((TO_W_(StgTSO_flags(CurrentTSO)) & TSO_INTERRUPTIBLE) == 0) { Sp_adj(-1); Sp(0) = stg_maskUninterruptiblezh_ret_info; } } StgTSO_flags(CurrentTSO) = %lobits32( TO_W_(StgTSO_flags(CurrentTSO)) | TSO_BLOCKEX | TSO_INTERRUPTIBLE); TICK_UNKNOWN_CALL(); TICK_SLOW_CALL_fast_v(); jump stg_ap_v_fast [R1]; } stg_maskUninterruptiblezh /* explicit stack */ { /* Args: R1 :: IO a */ STK_CHK_P_LL (WDS(1)/* worst case */, stg_maskUninterruptiblezh, R1); if ((TO_W_(StgTSO_flags(CurrentTSO)) & TSO_BLOCKEX) == 0) { /* avoid growing the stack unnecessarily */ if (Sp(0) == stg_maskUninterruptiblezh_ret_info) { Sp_adj(1); } else { Sp_adj(-1); Sp(0) = stg_unmaskAsyncExceptionszh_ret_info; } } else { if ((TO_W_(StgTSO_flags(CurrentTSO)) & TSO_INTERRUPTIBLE) != 0) { Sp_adj(-1); Sp(0) = stg_maskAsyncExceptionszh_ret_info; } } StgTSO_flags(CurrentTSO) = %lobits32( (TO_W_(StgTSO_flags(CurrentTSO)) | TSO_BLOCKEX) & ~TSO_INTERRUPTIBLE); TICK_UNKNOWN_CALL(); TICK_SLOW_CALL_fast_v(); jump stg_ap_v_fast [R1]; } stg_unmaskAsyncExceptionszh /* explicit stack */ { CInt r; W_ level; /* Args: R1 :: IO a */ P_ io; io = R1; STK_CHK_P_LL (WDS(4), stg_unmaskAsyncExceptionszh, io); /* 4 words: one for the unmask frame, 3 for setting up the * stack to call maybePerformBlockedException() below. */ /* If exceptions are already unmasked, there's nothing to do */ if ((TO_W_(StgTSO_flags(CurrentTSO)) & TSO_BLOCKEX) != 0) { /* avoid growing the stack unnecessarily */ if (Sp(0) == stg_unmaskAsyncExceptionszh_ret_info) { Sp_adj(1); } else { Sp_adj(-1); if ((TO_W_(StgTSO_flags(CurrentTSO)) & TSO_INTERRUPTIBLE) != 0) { Sp(0) = stg_maskAsyncExceptionszh_ret_info; } else { Sp(0) = stg_maskUninterruptiblezh_ret_info; } } StgTSO_flags(CurrentTSO) = %lobits32( TO_W_(StgTSO_flags(CurrentTSO)) & ~(TSO_BLOCKEX|TSO_INTERRUPTIBLE)); /* Eagerly raise a masked exception, if there is one */ if (StgTSO_blocked_exceptions(CurrentTSO) != END_TSO_QUEUE) { /* * We have to be very careful here, as in killThread#, since * we are about to raise an async exception in the current * thread, which might result in the thread being killed. * * Now, if we are to raise an exception in the current * thread, there might be an update frame above us on the * stack due to unsafePerformIO. Hence, the stack must * make sense, because it is about to be snapshotted into * an AP_STACK. */ Sp_adj(-3); Sp(2) = stg_ap_v_info; Sp(1) = io; Sp(0) = stg_enter_info; SAVE_THREAD_STATE(); (r) = ccall maybePerformBlockedException (MyCapability() "ptr", CurrentTSO "ptr"); if (r != 0::CInt) { if (StgTSO_what_next(CurrentTSO) == ThreadKilled::I16) { jump stg_threadFinished []; } else { LOAD_THREAD_STATE(); ASSERT(StgTSO_what_next(CurrentTSO) == ThreadRunGHC::I16); R1 = io; jump %ENTRY_CODE(Sp(0)) [R1]; } } else { /* we'll just call R1 directly, below */ Sp_adj(3); } } } TICK_UNKNOWN_CALL(); TICK_SLOW_CALL_fast_v(); R1 = io; jump stg_ap_v_fast [R1]; } stg_getMaskingStatezh () { /* args: none */ /* returns: 0 == unmasked, 1 == masked, non-interruptible, 2 == masked, interruptible */ return (((TO_W_(StgTSO_flags(CurrentTSO)) & TSO_BLOCKEX) != 0) + ((TO_W_(StgTSO_flags(CurrentTSO)) & TSO_INTERRUPTIBLE) != 0)); } stg_killThreadzh (P_ target, P_ exception) { W_ why_blocked; /* Needs 3 words because throwToSingleThreaded uses some stack */ STK_CHK_PP (WDS(3), stg_killThreadzh, target, exception); /* We call allocate in throwTo(), so better check for GC */ MAYBE_GC_PP (stg_killThreadzh, target, exception); /* * We might have killed ourselves. In which case, better be *very* * careful. If the exception killed us, then return to the scheduler. * If the exception went to a catch frame, we'll just continue from * the handler. */ if (target == CurrentTSO) { /* * So what should happen if a thread calls "throwTo self" inside * unsafePerformIO, and later the closure is evaluated by another * thread? Presumably it should behave as if throwTo just returned, * and then continue from there. See #3279, #3288. This is what * happens: on resumption, we will just jump to the next frame on * the stack, which is the return point for stg_killThreadzh. */ R1 = target; R2 = exception; jump stg_killMyself [R1,R2]; } else { W_ msg; ("ptr" msg) = ccall throwTo(MyCapability() "ptr", CurrentTSO "ptr", target "ptr", exception "ptr"); if (msg == NULL) { return (); } else { StgTSO_why_blocked(CurrentTSO) = BlockedOnMsgThrowTo; StgTSO_block_info(CurrentTSO) = msg; // we must block, and unlock the message before returning jump stg_block_throwto (target, exception); } } } /* * We must switch into low-level Cmm in order to raise an exception in * the current thread, hence this is in a separate proc with arguments * passed explicitly in R1 and R2. */ stg_killMyself { P_ target, exception; target = R1; exception = R2; SAVE_THREAD_STATE(); /* ToDo: what if the current thread is masking exceptions? */ ccall throwToSingleThreaded(MyCapability() "ptr", target "ptr", exception "ptr"); if (StgTSO_what_next(CurrentTSO) == ThreadKilled::I16) { jump stg_threadFinished []; } else { LOAD_THREAD_STATE(); ASSERT(StgTSO_what_next(CurrentTSO) == ThreadRunGHC::I16); jump %ENTRY_CODE(Sp(0)) []; } } /* ----------------------------------------------------------------------------- Catch frames -------------------------------------------------------------------------- */ /* Catch frames are very similar to update frames, but when entering * one we just pop the frame off the stack and perform the correct * kind of return to the activation record underneath us on the stack. */ #define CATCH_FRAME_FIELDS(w_,p_,info_ptr,p1,p2,exceptions_blocked,handler) \ w_ info_ptr, \ PROF_HDR_FIELDS(w_,p1,p2) \ w_ exceptions_blocked, \ p_ handler INFO_TABLE_RET(stg_catch_frame, CATCH_FRAME, CATCH_FRAME_FIELDS(W_,P_,info_ptr, p1, p2, exceptions_blocked,handler)) return (P_ ret) { return (ret); } /* ----------------------------------------------------------------------------- * The catch infotable * * This should be exactly the same as would be generated by this STG code * * catch = {x,h} \n {} -> catch#{x,h} * * It is used in deleteThread when reverting blackholes. * -------------------------------------------------------------------------- */ INFO_TABLE(stg_catch,2,0,FUN,"catch","catch") (P_ node) { jump stg_catchzh(StgClosure_payload(node,0),StgClosure_payload(node,1)); } stg_catchzh ( P_ io, /* :: IO a */ P_ handler /* :: Exception -> IO a */ ) { W_ exceptions_blocked; STK_CHK_GEN(); exceptions_blocked = TO_W_(StgTSO_flags(CurrentTSO)) & (TSO_BLOCKEX | TSO_INTERRUPTIBLE); TICK_CATCHF_PUSHED(); /* Apply R1 to the realworld token */ TICK_UNKNOWN_CALL(); TICK_SLOW_CALL_fast_v(); jump stg_ap_v_fast (CATCH_FRAME_FIELDS(,,stg_catch_frame_info, CCCS, 0, exceptions_blocked, handler)) (io); } /* ----------------------------------------------------------------------------- * The raise infotable * * This should be exactly the same as would be generated by this STG code * * raise = {err} \n {} -> raise#{err} * * It is used in stg_raisezh to update thunks on the update list * -------------------------------------------------------------------------- */ INFO_TABLE(stg_raise,1,0,THUNK_1_0,"raise","raise") { jump stg_raisezh(StgThunk_payload(R1,0)); } section "data" { no_break_on_exception: W_[1]; } INFO_TABLE_RET(stg_raise_ret, RET_SMALL, W_ info_ptr, P_ exception) return (P_ ret) { W_[no_break_on_exception] = 1; jump stg_raisezh (exception); } stg_raisezh /* explicit stack */ /* * args : R1 :: Exception * * Here we assume that the NativeNodeCall convention always puts the * first argument in R1 (which it does). We cannot use high-level cmm * due to all the LOAD_THREAD_STATE()/SAVE_THREAD_STATE() and stack * walking that happens in here. */ { W_ handler; W_ frame_type; W_ exception; exception = R1; #if defined(PROFILING) /* Debugging tool: on raising an exception, show where we are. */ /* ToDo: currently this is a hack. Would be much better if * the info was only displayed for an *uncaught* exception. */ if (RtsFlags_ProfFlags_showCCSOnException(RtsFlags) != 0::CBool) { SAVE_THREAD_STATE(); ccall fprintCCS_stderr(CCCS "ptr", exception "ptr", CurrentTSO "ptr"); LOAD_THREAD_STATE(); } #endif retry_pop_stack: SAVE_THREAD_STATE(); (frame_type) = ccall raiseExceptionHelper(BaseReg "ptr", CurrentTSO "ptr", exception "ptr"); LOAD_THREAD_STATE(); if (frame_type == ATOMICALLY_FRAME) { /* The exception has reached the edge of a memory transaction. Check that * the transaction is valid. If not then perhaps the exception should * not have been thrown: re-run the transaction. "trec" will either be * a top-level transaction running the atomic block, or a nested * transaction running an invariant check. In the latter case we * abort and de-allocate the top-level transaction that encloses it * as well (we could just abandon its transaction record, but this makes * sure it's marked as aborted and available for re-use). */ W_ trec, outer; W_ r; trec = StgTSO_trec(CurrentTSO); (r) = ccall stmValidateNestOfTransactions(MyCapability() "ptr", trec "ptr"); outer = StgTRecHeader_enclosing_trec(trec); ccall stmAbortTransaction(MyCapability() "ptr", trec "ptr"); ccall stmFreeAbortedTRec(MyCapability() "ptr", trec "ptr"); if (outer != NO_TREC) { ccall stmAbortTransaction(MyCapability() "ptr", outer "ptr"); ccall stmFreeAbortedTRec(MyCapability() "ptr", outer "ptr"); } StgTSO_trec(CurrentTSO) = NO_TREC; if (r != 0) { // Transaction was valid: continue searching for a catch frame Sp = Sp + SIZEOF_StgAtomicallyFrame; goto retry_pop_stack; } else { // Transaction was not valid: we retry the exception (otherwise continue // with a further call to raiseExceptionHelper) ("ptr" trec) = ccall stmStartTransaction(MyCapability() "ptr", NO_TREC "ptr"); StgTSO_trec(CurrentTSO) = trec; R1 = StgAtomicallyFrame_code(Sp); jump stg_ap_v_fast [R1]; } } // After stripping the stack, see whether we should break here for // GHCi (c.f. the -fbreak-on-exception flag). We do this after // stripping the stack for a reason: we'll be inspecting values in // GHCi, and it helps if all the thunks under evaluation have // already been updated with the exception, rather than being left // as blackholes. if (W_[no_break_on_exception] != 0) { W_[no_break_on_exception] = 0; } else { if (TO_W_(CInt[rts_stop_on_exception]) != 0) { W_ ioAction; // we don't want any further exceptions to be caught, // until GHCi is ready to handle them. This prevents // deadlock if an exception is raised in InteractiveUI, // for exmplae. Perhaps the stop_on_exception flag should // be per-thread. CInt[rts_stop_on_exception] = 0; ("ptr" ioAction) = ccall deRefStablePtr (W_[rts_breakpoint_io_action] "ptr"); Sp = Sp - WDS(9); Sp(8) = exception; Sp(7) = stg_raise_ret_info; Sp(6) = exception; Sp(5) = ghczmprim_GHCziTypes_True_closure; // True <=> a breakpoint Sp(4) = stg_ap_ppv_info; Sp(3) = 0; Sp(2) = stg_ap_n_info; Sp(1) = 0; R1 = ioAction; jump RET_LBL(stg_ap_n) [R1]; } } if (frame_type == STOP_FRAME) { /* * We've stripped the entire stack, the thread is now dead. * We will leave the stack in a GC'able state, see the stg_stop_thread * entry code in StgStartup.cmm. */ W_ stack; stack = StgTSO_stackobj(CurrentTSO); Sp = stack + OFFSET_StgStack_stack + WDS(TO_W_(StgStack_stack_size(stack))) - WDS(2); Sp(1) = exception; /* save the exception */ Sp(0) = stg_enter_info; /* so that GC can traverse this stack */ StgTSO_what_next(CurrentTSO) = ThreadKilled::I16; SAVE_THREAD_STATE(); /* inline! */ jump stg_threadFinished []; } /* Ok, Sp points to the enclosing CATCH_FRAME or CATCH_STM_FRAME. * Pop everything down to and including this frame, update Su, * push R1, and enter the handler. */ if (frame_type == CATCH_FRAME) { handler = StgCatchFrame_handler(Sp); } else { handler = StgCatchSTMFrame_handler(Sp); } /* Restore the masked/unmasked state for asynchronous exceptions * at the CATCH_FRAME. * * If exceptions were unmasked, arrange that they are unmasked * again after executing the handler by pushing an * unmaskAsyncExceptions_ret stack frame. * * If we've reached an STM catch frame then roll back the nested * transaction we were using. */ W_ frame; frame = Sp; if (frame_type == CATCH_FRAME) { Sp = Sp + SIZEOF_StgCatchFrame; if ((StgCatchFrame_exceptions_blocked(frame) & TSO_BLOCKEX) == 0) { Sp_adj(-1); Sp(0) = stg_unmaskAsyncExceptionszh_ret_info; } /* Ensure that async exceptions are masked when running the handler. */ StgTSO_flags(CurrentTSO) = %lobits32( TO_W_(StgTSO_flags(CurrentTSO)) | TSO_BLOCKEX | TSO_INTERRUPTIBLE); /* The interruptible state is inherited from the context of the * catch frame, but note that TSO_INTERRUPTIBLE is only meaningful * if TSO_BLOCKEX is set. (we got this wrong earlier, and #4988 * was a symptom of the bug). */ if ((StgCatchFrame_exceptions_blocked(frame) & (TSO_BLOCKEX | TSO_INTERRUPTIBLE)) == TSO_BLOCKEX) { StgTSO_flags(CurrentTSO) = %lobits32( TO_W_(StgTSO_flags(CurrentTSO)) & ~TSO_INTERRUPTIBLE); } } else /* CATCH_STM_FRAME */ { W_ trec, outer; trec = StgTSO_trec(CurrentTSO); outer = StgTRecHeader_enclosing_trec(trec); ccall stmAbortTransaction(MyCapability() "ptr", trec "ptr"); ccall stmFreeAbortedTRec(MyCapability() "ptr", trec "ptr"); StgTSO_trec(CurrentTSO) = outer; Sp = Sp + SIZEOF_StgCatchSTMFrame; } /* Call the handler, passing the exception value and a realworld * token as arguments. */ Sp_adj(-1); Sp(0) = exception; R1 = handler; Sp_adj(-1); TICK_UNKNOWN_CALL(); TICK_SLOW_CALL_fast_pv(); jump RET_LBL(stg_ap_pv) [R1]; } stg_raiseIOzh (P_ exception) { jump stg_raisezh (exception); }