{-# LANGUAGE GADTs #-}
module GHC.Driver.GenerateCgIPEStub (generateCgIPEStub) where
import qualified Data.Map.Strict as Map
import Data.Maybe (mapMaybe, listToMaybe)
import GHC.Cmm
import GHC.Cmm.CLabel (CLabel)
import GHC.Cmm.Dataflow (Block, C, O)
import GHC.Cmm.Dataflow.Block (blockSplit, blockToList)
import GHC.Cmm.Dataflow.Collections (mapToList)
import GHC.Cmm.Dataflow.Label (Label)
import GHC.Cmm.Info.Build (emptySRT)
import GHC.Cmm.Pipeline (cmmPipeline)
import GHC.Data.Maybe (firstJusts)
import GHC.Data.Stream (Stream, liftIO)
import qualified GHC.Data.Stream as Stream
import GHC.Driver.Env (hsc_dflags, hsc_logger)
import GHC.Driver.Env.Types (HscEnv)
import GHC.Driver.Flags (GeneralFlag (Opt_InfoTableMap))
import GHC.Driver.Session (gopt, targetPlatform)
import GHC.Driver.Config.StgToCmm
import GHC.Driver.Config.Cmm
import GHC.Prelude
import GHC.Runtime.Heap.Layout (isStackRep)
import GHC.Settings (Platform, platformTablesNextToCode)
import GHC.StgToCmm.Monad (getCmm, initC, runC, initFCodeState)
import GHC.StgToCmm.Prof (initInfoTableProv)
import GHC.StgToCmm.Types (CmmCgInfos (..), ModuleLFInfos)
import GHC.Types.IPE (InfoTableProvMap (provInfoTables), IpeSourceLocation)
import GHC.Types.Name.Set (NonCaffySet)
import GHC.Types.Tickish (GenTickish (SourceNote))
import GHC.Unit.Types (Module)
import GHC.Utils.Misc
{-
Note [Stacktraces from Info Table Provenance Entries (IPE based stack unwinding)]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Stacktraces can be created from return frames as they are pushed to stack for every case scrutinee.
But to make them readable / meaningful, one needs to know the source location of each return frame.
Every return frame has a distinct info table and thus a distinct code pointer (for tables next to
code) or at least a distinct address itself. Info Table Provenance Entries (IPEs) are searchable by
this pointer and contain a source location.
The info table / info table code pointer to source location map is described in:
Note [Mapping Info Tables to Source Positions]
To be able to lookup IPEs for return frames one needs to emit them during compile time. This is done
by `generateCgIPEStub`.
This leads to the question: How to figure out the source location of a return frame?
While the lookup algorithms when tables-next-to-code is on/off differ in details, they have in
common that we want to lookup the `CmmNode.CmmTick` (containing a `SourceNote`) that is nearest
(before) the usage of the return frame's label. (Which label and label type is used differs between
these two use cases.)
With tables-next-to-code
~~~~~~~~~~~~~~~~~~~~~~~~
Let's consider this example:
```
Main.returnFrame_entry() { // [R2]
{ info_tbls: [(c18g,
label: block_c18g_info
rep: StackRep []
srt: Just GHC.CString.unpackCString#_closure),
(c18r,
label: Main.returnFrame_info
rep: HeapRep static { Fun {arity: 1 fun_type: ArgSpec 5} }
srt: Nothing)]
stack_info: arg_space: 8
}
{offset
[...]
c18u: // global
//tick src<Main.hs:(7,1)-(16,15)>
I64[Hp - 16] = sat_s16B_info;
P64[Hp] = _s16r::P64;
_c17j::P64 = Hp - 16;
//tick src<Main.hs:8:25-39>
I64[Sp - 8] = c18g;
R3 = _c17j::P64;
R2 = GHC.IO.Unsafe.unsafePerformIO_closure;
R1 = GHC.Base.$_closure;
Sp = Sp - 8;
call stg_ap_pp_fast(R3,
R2,
R1) returns to c18g, args: 8, res: 8, upd: 8;
```
The return frame `block_c18g_info` has the label `c18g` which is used in the call to `stg_ap_pp_fast`
(`returns to c18g`) as continuation (`cml_cont`). The source location we're after, is the nearest
`//tick` before the call (`//tick src<Main.hs:8:25-39>`).
In code the Cmm program is represented as a Hoopl graph. Hoopl distinguishes nodes by defining if they
are open or closed on entry (one can fallthrough to them from the previous instruction) and if they are
open or closed on exit (one can fallthrough from them to the next node).
Please refer to the paper "Hoopl: A Modular, Reusable Library for Dataflow Analysis and Transformation"
for a detailed explanation.
Here we use the fact, that calls (represented by `CmmNode.CmmCall`) are always closed on exit
(`CmmNode O C`, `O` means open, `C` closed). In other words, they are always at the end of a block.
So, given a stack represented info table (likely representing a return frame, but this isn't completely
sure as there are e.g. update frames, too) with it's label (`c18g` in the example above) and a `CmmGraph`:
- Look at the end of every block, if it's a `CmmNode.CmmCall` returning to the continuation with the
label of the return frame.
- If there's such a call, lookup the nearest `CmmNode.CmmTick` by traversing the middle part of the block
backwards (from end to beginning).
- Take the first `CmmNode.CmmTick` that contains a `Tickish.SourceNote` and return it's payload as
`IpeSourceLocation`. (There are other `Tickish` constructors like `ProfNote` or `HpcTick`, these are
ignored.)
Without tables-next-to-code
~~~~~~~~~~~~~~~~~~~~~~~~~~~
When tables-next-to-code is off, there is no return frame / continuation label in calls. The continuation (i.e. return
frame) is set in an explicit Cmm assignment. Thus the tick lookup algorithm has to be slightly different.
```
sat_s16G_entry() { // [R1]
{ info_tbls: [(c18O,
label: sat_s16G_info
rep: HeapRep { Thunk }
srt: Just _u18Z_srt)]
stack_info: arg_space: 0
}
{offset
c18O: // global
_s16G::P64 = R1;
if ((Sp + 8) - 40 < SpLim) (likely: False) goto c18P; else goto c18Q;
c18P: // global
R1 = _s16G::P64;
call (stg_gc_enter_1)(R1) args: 8, res: 0, upd: 8;
c18Q: // global
I64[Sp - 16] = stg_upd_frame_info;
P64[Sp - 8] = _s16G::P64;
//tick src<Main.hs:20:9-13>
I64[Sp - 24] = block_c18M_info;
R1 = GHC.Show.$fShow[]_closure;
P64[Sp - 32] = GHC.Show.$fShowChar_closure;
Sp = Sp - 32;
call stg_ap_p_fast(R1) args: 16, res: 8, upd: 24;
}
},
_blk_c18M() { // [R1]
{ info_tbls: [(c18M,
label: block_c18M_info
rep: StackRep []
srt: Just System.IO.print_closure)]
stack_info: arg_space: 0
}
{offset
c18M: // global
_s16F::P64 = R1;
R1 = System.IO.print_closure;
P64[Sp] = _s16F::P64;
call stg_ap_p_fast(R1) args: 32, res: 0, upd: 24;
}
},
```
In this example we have to lookup `//tick src<Main.hs:20:9-13>` for the return frame `c18M`.
Notice, that this cannot be done with the `Label` `c18M`, but with the `CLabel` `block_c18M_info`
(`label: block_c18M_info` is actually a `CLabel`).
The find the tick:
- Every `Block` is checked from top (first) to bottom (last) node for an assignment like
`I64[Sp - 24] = block_c18M_info;`. The lefthand side is actually ignored.
- If such an assignment is found the search is over, because the payload (content of
`Tickish.SourceNote`, represented as `IpeSourceLocation`) of last visited tick is always
remembered in a `Maybe`.
-}
generateCgIPEStub :: HscEnv -> Module -> InfoTableProvMap -> Stream IO CmmGroupSRTs (NonCaffySet, ModuleLFInfos) -> Stream IO CmmGroupSRTs CmmCgInfos
generateCgIPEStub hsc_env this_mod denv s = do
let dflags = hsc_dflags hsc_env
platform = targetPlatform dflags
logger = hsc_logger hsc_env
fstate = initFCodeState platform
cmm_cfg = initCmmConfig dflags
cgState <- liftIO initC
-- Collect info tables, but only if -finfo-table-map is enabled, otherwise labeledInfoTablesWithTickishes is empty.
let collectFun = if gopt Opt_InfoTableMap dflags then collect platform else collectNothing
(labeledInfoTablesWithTickishes, (nonCaffySet, moduleLFInfos)) <- Stream.mapAccumL_ collectFun [] s
-- Yield Cmm for Info Table Provenance Entries (IPEs)
let denv' = denv {provInfoTables = Map.fromList (map (\(_, i, t) -> (cit_lbl i, t)) labeledInfoTablesWithTickishes)}
((ipeStub, ipeCmmGroup), _) = runC (initStgToCmmConfig dflags this_mod) fstate cgState $ getCmm (initInfoTableProv (map sndOf3 labeledInfoTablesWithTickishes) denv')
(_, ipeCmmGroupSRTs) <- liftIO $ cmmPipeline logger cmm_cfg (emptySRT this_mod) ipeCmmGroup
Stream.yield ipeCmmGroupSRTs
return CmmCgInfos {cgNonCafs = nonCaffySet, cgLFInfos = moduleLFInfos, cgIPEStub = ipeStub}
where
collect :: Platform -> [(Label, CmmInfoTable, Maybe IpeSourceLocation)] -> CmmGroupSRTs -> IO ([(Label, CmmInfoTable, Maybe IpeSourceLocation)], CmmGroupSRTs)
collect platform acc cmmGroupSRTs = do
let labelsToInfoTables = collectInfoTables cmmGroupSRTs
labelsToInfoTablesToTickishes = map (\(l, i) -> (l, i, lookupEstimatedTick platform cmmGroupSRTs l i)) labelsToInfoTables
return (acc ++ labelsToInfoTablesToTickishes, cmmGroupSRTs)
collectNothing :: [a] -> CmmGroupSRTs -> IO ([a], CmmGroupSRTs)
collectNothing _ cmmGroupSRTs = pure ([], cmmGroupSRTs)
collectInfoTables :: CmmGroupSRTs -> [(Label, CmmInfoTable)]
collectInfoTables cmmGroup = concat $ mapMaybe extractInfoTables cmmGroup
extractInfoTables :: GenCmmDecl RawCmmStatics CmmTopInfo CmmGraph -> Maybe [(Label, CmmInfoTable)]
extractInfoTables (CmmProc h _ _ _) = Just $ mapToList (info_tbls h)
extractInfoTables _ = Nothing
lookupEstimatedTick :: Platform -> CmmGroupSRTs -> Label -> CmmInfoTable -> Maybe IpeSourceLocation
lookupEstimatedTick platform cmmGroup infoTableLabel infoTable = do
-- All return frame info tables are stack represented, though not all stack represented info
-- tables have to be return frames.
if (isStackRep . cit_rep) infoTable
then do
let findFun =
if platformTablesNextToCode platform
then findCmmTickishWithTNTC infoTableLabel
else findCmmTickishSansTNTC (cit_lbl infoTable)
blocks = concatMap toBlockList (graphs cmmGroup)
firstJusts $ map findFun blocks
else Nothing
graphs :: CmmGroupSRTs -> [CmmGraph]
graphs = foldl' go []
where
go :: [CmmGraph] -> GenCmmDecl d h CmmGraph -> [CmmGraph]
go acc (CmmProc _ _ _ g) = g : acc
go acc _ = acc
findCmmTickishWithTNTC :: Label -> Block CmmNode C C -> Maybe IpeSourceLocation
findCmmTickishWithTNTC label block = do
let (_, middleBlock, endBlock) = blockSplit block
isCallWithReturnFrameLabel endBlock label
lastTickInBlock middleBlock
where
isCallWithReturnFrameLabel :: CmmNode O C -> Label -> Maybe ()
isCallWithReturnFrameLabel (CmmCall _ (Just l) _ _ _ _) clabel | l == clabel = Just ()
isCallWithReturnFrameLabel _ _ = Nothing
lastTickInBlock block =
listToMaybe $
mapMaybe maybeTick $ (reverse . blockToList) block
maybeTick :: CmmNode O O -> Maybe IpeSourceLocation
maybeTick (CmmTick (SourceNote span name)) = Just (span, name)
maybeTick _ = Nothing
findCmmTickishSansTNTC :: CLabel -> Block CmmNode C C -> Maybe IpeSourceLocation
findCmmTickishSansTNTC cLabel block = do
let (_, middleBlock, _) = blockSplit block
find cLabel (blockToList middleBlock) Nothing
where
find :: CLabel -> [CmmNode O O] -> Maybe IpeSourceLocation -> Maybe IpeSourceLocation
find label (b : blocks) lastTick = case b of
(CmmStore _ (CmmLit (CmmLabel l)) _) -> if label == l then lastTick else find label blocks lastTick
(CmmTick (SourceNote span name)) -> find label blocks $ Just (span, name)
_ -> find label blocks lastTick
find _ [] _ = Nothing