diff options
| -rw-r--r-- | compiler/GHC/Platform.hs | 62 | ||||
| -rw-r--r-- | compiler/GHC/Unit/State.hs | 40 | ||||
| -rw-r--r-- | includes/Cmm.h | 4 | ||||
| -rw-r--r-- | includes/rts/Constants.h | 2 |
4 files changed, 79 insertions, 29 deletions
diff --git a/compiler/GHC/Platform.hs b/compiler/GHC/Platform.hs index 5ce843046b..b3ab1b4020 100644 --- a/compiler/GHC/Platform.hs +++ b/compiler/GHC/Platform.hs @@ -1,11 +1,10 @@ {-# LANGUAGE ScopedTypeVariables #-} +{-# LANGUAGE LambdaCase #-} -- | Platform description module GHC.Platform ( Platform (..) - , platformConstants , PlatformWordSize(..) - , PlatformConstants(..) , platformArch , platformOS , ArchOS(..) @@ -33,6 +32,10 @@ module GHC.Platform , PlatformMisc(..) , SseVersion (..) , BmiVersion (..) + -- * Platform constants + , PlatformConstants(..) + , lookupPlatformConstants + , platformConstants -- * Shared libraries , platformSOName , platformHsSOName @@ -51,6 +54,7 @@ import GHC.Utils.Panic.Plain import Data.Word import Data.Int import System.FilePath +import System.Directory -- | Platform description -- @@ -249,3 +253,57 @@ platformSOExt platform OSDarwin -> "dylib" OSMinGW32 -> "dll" _ -> "so" + +-- Note [Platform constants] +-- ~~~~~~~~~~~~~~~~~~~~~~~~~ +-- +-- The RTS is partly written in C, hence we use an external C compiler to build +-- it. Thus GHC must somehow retrieve some information about the produced code +-- (sizes of types, offsets of struct fields, etc.) to produce compatible code. +-- +-- This is the role of utils/deriveConstants utility: it produces a C +-- source, compiles it with the same toolchain that will be used to build the +-- RTS, and finally retrieves the constants from the built artefact. We can't +-- directly run the produced program because we may be cross-compiling. +-- +-- These constants are then stored in DerivedConstants.h header file that is +-- bundled with the RTS unit. This file is directly imported by Cmm codes and it +-- is also read by GHC. deriveConstants also produces the Haskell definition of +-- the PlatformConstants datatype and the Haskell parser for the +-- DerivedConstants.h file. +-- +-- For quite some time, constants used by GHC were globally installed in +-- ${libdir}/platformConstants but now GHC reads the DerivedConstants.h header +-- bundled with the RTS unit. GHC detects when it builds the RTS unit itself and +-- in this case it loads the header from the include-dirs passed on the +-- command-line. +-- +-- Note that GHC doesn't parse every "#define SOME_CONSTANT 123" individually. +-- Instead there is a single #define that contains all the constants useful to +-- GHC in a comma separated list: +-- +-- #define HS_CONSTANTS "123,45,..." +-- +-- Note that GHC mustn't directly import DerivedConstants.h as these constants +-- are only valid for a specific target platform and we want GHC to be target +-- agnostic. +-- + + +-- | Try to locate "DerivedConstants.h" file in the given dirs and to parse the +-- PlatformConstants from it. +-- +-- See Note [Platform constants] +lookupPlatformConstants :: [FilePath] -> IO (Maybe PlatformConstants) +lookupPlatformConstants include_dirs = find_constants include_dirs + where + try_parse d = do + let p = d </> "DerivedConstants.h" + doesFileExist p >>= \case + True -> Just <$> parseConstantsHeader p + False -> return Nothing + + find_constants [] = return Nothing + find_constants (x:xs) = try_parse x >>= \case + Nothing -> find_constants xs + Just c -> return (Just c) diff --git a/compiler/GHC/Unit/State.hs b/compiler/GHC/Unit/State.hs index 4a1cd29b25..fe4796d1fc 100644 --- a/compiler/GHC/Unit/State.hs +++ b/compiler/GHC/Unit/State.hs @@ -77,7 +77,6 @@ import GHC.Driver.Session import GHC.Platform import GHC.Platform.Ways -import GHC.Platform.Constants import GHC.Unit.Database import GHC.Unit.Info @@ -596,29 +595,22 @@ initUnits logger dflags cached_dbs = do (homeUnitInstanceOf_ dflags) (homeUnitInstantiations_ dflags) - -- try to find platform constants - mconstants <- do - let - try_parse d = do - let p = d </> "DerivedConstants.h" - doesFileExist p >>= \case - True -> Just <$> parseConstantsHeader p - False -> return Nothing - - find_constants [] = return Nothing - find_constants (x:xs) = try_parse x >>= \case - Nothing -> find_constants xs - Just c -> return (Just c) - - if homeUnitId_ dflags == rtsUnitId - then do - -- we're building the RTS! Try to find the header in its includes - find_constants (includePathsGlobal (includePaths dflags)) - else - -- try to find the platform constants in the RTS unit - case lookupUnitId unit_state rtsUnitId of - Nothing -> return Nothing - Just info -> find_constants (fmap ST.unpack (unitIncludeDirs info)) + -- Try to find platform constants + -- + -- See Note [Platform constants] in GHC.Platform + mconstants <- if homeUnitId_ dflags == rtsUnitId + then do + -- we're building the RTS! Lookup DerivedConstants.h in the include paths + lookupPlatformConstants (includePathsGlobal (includePaths dflags)) + else + -- lookup the DerivedConstants.h header bundled with the RTS unit. We + -- don't fail if we can't find the RTS unit as it can be a valid (but + -- uncommon) case, e.g. building a C utility program (not depending on the + -- RTS) before building the RTS. In any case, we will fail later on if we + -- really need to use the platform constants but they have not been loaded. + case lookupUnitId unit_state rtsUnitId of + Nothing -> return Nothing + Just info -> lookupPlatformConstants (fmap ST.unpack (unitIncludeDirs info)) return (dbs,unit_state,home_unit,mconstants) diff --git a/includes/Cmm.h b/includes/Cmm.h index 84c6fca125..b1b8680e99 100644 --- a/includes/Cmm.h +++ b/includes/Cmm.h @@ -20,8 +20,8 @@ * StgTSO_what_next(CurrentTSO) = x * * where the StgTSO_what_next() macro is automatically generated by - * mkDerivedConstants.c. If you need to access a field that doesn't - * already have a macro, edit that file (it's pretty self-explanatory). + * utils/deriveConstants. If you need to access a field that doesn't + * already have a macro, edit that program (it's pretty self-explanatory). * * -------------------------------------------------------------------------- */ diff --git a/includes/rts/Constants.h b/includes/rts/Constants.h index 043099bd1a..9cbe47752e 100644 --- a/includes/rts/Constants.h +++ b/includes/rts/Constants.h @@ -10,7 +10,7 @@ * * Constants which are derived automatically from other definitions in * the system (eg. structure sizes) are generated into the file - * DerivedConstants.h by a C program (mkDerivedConstantsHdr). + * DerivedConstants.h by a C program (utils/deriveConstants). * * To understand the structure of the RTS headers, see the wiki: * https://gitlab.haskell.org/ghc/ghc/wikis/commentary/source-tree/includes |