Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC Commits: 2433e91d by Cheng Shao at 2026-01-09T20:24:43-05:00 compiler: change sectionProtection to take SectionType argument This commit changes `sectionProtection` to only take `SectionType` argument instead of whole `Section`, since it doesn't need the Cmm section content anyway, and it can then be called in parts of NCG where we only have a `SectionType` in scope. - - - - - e5926fbe by Cheng Shao at 2026-01-09T20:24:43-05:00 compiler: change isInitOrFiniSection to take SectionType argument This commit changes `isInitOrFiniSection` to only take `SectionType` argument instead of whole `Section`, since it doesn't need the Cmm section content anyway, and it can then be called in parts of NCG where we only have a `SectionType` in scope. Also marks it as exported. - - - - - 244d57d7 by Cheng Shao at 2026-01-09T20:24:43-05:00 compiler: fix split sections on windows This patch fixes split sections on windows by emitting the right COMDAT section header in NCG, see added comment for more explanation. Fix #26696 #26494. ------------------------- Metric Decrease: LargeRecord T9675 size_hello_artifact size_hello_artifact_gzip size_hello_unicode size_hello_unicode_gzip Metric Increase: T13035 ------------------------- Co-authored-by: Codex <codex@openai.com> - - - - - 8 changed files: - compiler/GHC/Cmm.hs - compiler/GHC/Cmm/InitFini.hs - compiler/GHC/CmmToAsm/AArch64/Ppr.hs - compiler/GHC/CmmToAsm/Ppr.hs - compiler/GHC/CmmToAsm/Wasm/FromCmm.hs - compiler/GHC/CmmToAsm/X86/Ppr.hs - compiler/GHC/CmmToC.hs - compiler/GHC/CmmToLlvm/Data.hs Changes: ===================================== compiler/GHC/Cmm.hs ===================================== @@ -278,8 +278,8 @@ data SectionProtection deriving (Eq) -- | Should a data in this section be considered constant at runtime -sectionProtection :: Section -> SectionProtection -sectionProtection (Section t _) = case t of +sectionProtection :: SectionType -> SectionProtection +sectionProtection t = case t of Text -> ReadOnlySection ReadOnlyData -> ReadOnlySection RelocatableReadOnlyData -> WriteProtectedSection ===================================== compiler/GHC/Cmm/InitFini.hs ===================================== @@ -2,6 +2,7 @@ module GHC.Cmm.InitFini ( InitOrFini(..) , isInitOrFiniArray + , isInitOrFiniSection ) where import GHC.Prelude @@ -63,8 +64,8 @@ finalizer CmmDecl will be emitted per module. data InitOrFini = IsInitArray | IsFiniArray isInitOrFiniArray :: RawCmmDecl -> Maybe (InitOrFini, [CLabel]) -isInitOrFiniArray (CmmData sect (CmmStaticsRaw _ lits)) - | Just initOrFini <- isInitOrFiniSection sect +isInitOrFiniArray (CmmData (Section t _) (CmmStaticsRaw _ lits)) + | Just initOrFini <- isInitOrFiniSection t = Just (initOrFini, map get_label lits) where get_label :: CmmStatic -> CLabel @@ -72,7 +73,7 @@ isInitOrFiniArray (CmmData sect (CmmStaticsRaw _ lits)) get_label static = pprPanic "isInitOrFiniArray: invalid entry" (ppr static) isInitOrFiniArray _ = Nothing -isInitOrFiniSection :: Section -> Maybe InitOrFini -isInitOrFiniSection (Section InitArray _) = Just IsInitArray -isInitOrFiniSection (Section FiniArray _) = Just IsFiniArray +isInitOrFiniSection :: SectionType -> Maybe InitOrFini +isInitOrFiniSection InitArray = Just IsInitArray +isInitOrFiniSection FiniArray = Just IsFiniArray isInitOrFiniSection _ = Nothing ===================================== compiler/GHC/CmmToAsm/AArch64/Ppr.hs ===================================== @@ -19,6 +19,7 @@ import GHC.Cmm.Dataflow.Label import GHC.Cmm.BlockId import GHC.Cmm.CLabel +import GHC.Cmm.InitFini import GHC.Types.Unique ( pprUniqueAlways, getUnique ) import GHC.Platform @@ -28,9 +29,7 @@ import GHC.Utils.Panic pprNatCmmDecl :: IsDoc doc => NCGConfig -> NatCmmDecl RawCmmStatics Instr -> doc pprNatCmmDecl config (CmmData section dats) = - let platform = ncgPlatform config - in - pprSectionAlign config section $$ pprDatas platform dats + pprSectionAlign config section $$ pprDatas config dats pprNatCmmDecl config proc@(CmmProc top_info lbl _ (ListGraph blocks)) = let platform = ncgPlatform config @@ -91,9 +90,20 @@ pprAlignForSection _platform _seg -- .balign 8 -- pprSectionAlign :: IsDoc doc => NCGConfig -> Section -> doc -pprSectionAlign config sec@(Section seg _) = +pprSectionAlign config sec@(Section seg suffix) = line (pprSectionHeader config sec) + $$ coffSplitSectionComdatKey $$ pprAlignForSection (ncgPlatform config) seg + where + platform = ncgPlatform config + -- See Note [Split sections on COFF objects] + coffSplitSectionComdatKey + | OSMinGW32 <- platformOS platform + , ncgSplitSections config + , Nothing <- isInitOrFiniSection seg + = line (pprCOFFComdatKey platform suffix <> colon) + | otherwise + = empty -- | Output the ELF .size directive. pprSizeDecl :: IsDoc doc => Platform -> CLabel -> doc @@ -136,20 +146,26 @@ pprBasicBlock platform with_dwarf info_env (BasicBlock blockid instrs) (l@LOCATION{} : _) -> pprInstr platform l _other -> empty -pprDatas :: IsDoc doc => Platform -> RawCmmStatics -> doc +pprDatas :: IsDoc doc => NCGConfig -> RawCmmStatics -> doc -- See Note [emit-time elimination of static indirections] in "GHC.Cmm.CLabel". -pprDatas platform (CmmStaticsRaw alias [CmmStaticLit (CmmLabel lbl), CmmStaticLit ind, _, _]) +pprDatas config (CmmStaticsRaw alias [CmmStaticLit (CmmLabel lbl), CmmStaticLit ind, _, _]) | lbl == mkIndStaticInfoLabel , let labelInd (CmmLabelOff l _) = Just l labelInd (CmmLabel l) = Just l labelInd _ = Nothing , Just ind' <- labelInd ind , alias `mayRedirectTo` ind' + -- See Note [Split sections on COFF objects] + , not $ platformOS platform == OSMinGW32 && ncgSplitSections config = pprGloblDecl platform alias $$ line (text ".equiv" <+> pprAsmLabel platform alias <> comma <> pprAsmLabel platform ind') + where + platform = ncgPlatform config -pprDatas platform (CmmStaticsRaw lbl dats) +pprDatas config (CmmStaticsRaw lbl dats) = vcat (pprLabel platform lbl : map (pprData platform) dats) + where + platform = ncgPlatform config pprData :: IsDoc doc => Platform -> CmmStatic -> doc pprData _platform (CmmString str) = line (pprString str) ===================================== compiler/GHC/CmmToAsm/Ppr.hs ===================================== @@ -1,4 +1,5 @@ {-# LANGUAGE MagicHash #-} +{-# LANGUAGE MultiWayIf #-} ----------------------------------------------------------------------------- -- @@ -14,6 +15,7 @@ module GHC.CmmToAsm.Ppr ( pprASCII, pprString, pprFileEmbed, + pprCOFFComdatKey, pprSectionHeader ) @@ -23,6 +25,7 @@ import GHC.Prelude import GHC.Utils.Asm import GHC.Cmm.CLabel +import GHC.Cmm.InitFini import GHC.Cmm import GHC.CmmToAsm.Config import GHC.Utils.Outputable as SDoc @@ -220,8 +223,8 @@ pprGNUSectionHeader config t suffix = | otherwise -> text ".rodata" RelocatableReadOnlyData | OSMinGW32 <- platformOS platform -- Concept does not exist on Windows, - -- So map these to R/O data. - -> text ".rdata$rel.ro" + -- So map these to data. + -> text ".data" | otherwise -> text ".data.rel.ro" UninitialisedData -> text ".bss" InitArray @@ -240,24 +243,79 @@ pprGNUSectionHeader config t suffix = | OSMinGW32 <- platformOS platform -> text ".rdata" | otherwise -> text ".ipe" - flags = case t of - Text - | OSMinGW32 <- platformOS platform, splitSections - -> text ",\"xr\"" - | splitSections - -> text ",\"ax\"," <> sectionType platform "progbits" - CString - | OSMinGW32 <- platformOS platform - -> empty - | otherwise -> text ",\"aMS\"," <> sectionType platform "progbits" <> text ",1" - IPE - | OSMinGW32 <- platformOS platform - -> empty - | otherwise -> text ",\"a\"," <> sectionType platform "progbits" - _ -> empty + flags + -- See + -- https://github.com/llvm/llvm-project/blob/llvmorg-21.1.8/lld/COFF/Chunks.cpp... + -- and https://llvm.org/docs/Extensions.html#section-directive. + -- LLD COFF backend gc-sections only work on COMDAT sections so + -- we need to mark it as a COMDAT section. You can use clang64 + -- toolchain to compile small examples with + -- `-ffunction-sections -fdata-sections -S` to see these section + -- headers in the wild. Also see Note [Split sections on COFF objects] + -- below. + | OSMinGW32 <- platformOS platform, + splitSections = + if + | Just _ <- isInitOrFiniSection t -> text ",\"dw\"" + | otherwise -> + let coff_section_flags + | Text <- t = "xr" + | UninitialisedData <- t = "bw" + | ReadOnlySection <- sectionProtection t = "dr" + | otherwise = "dw" + in hcat + [ text ",\"", + text coff_section_flags, + text "\",one_only,", + pprCOFFComdatKey platform suffix + ] + | otherwise = + case t of + Text + | splitSections + -> text ",\"ax\"," <> sectionType platform "progbits" + CString + | OSMinGW32 <- platformOS platform + -> empty + | otherwise -> text ",\"aMS\"," <> sectionType platform "progbits" <> text ",1" + IPE + | OSMinGW32 <- platformOS platform + -> empty + | otherwise -> text ",\"a\"," <> sectionType platform "progbits" + _ -> empty {-# SPECIALIZE pprGNUSectionHeader :: NCGConfig -> SectionType -> CLabel -> SDoc #-} {-# SPECIALIZE pprGNUSectionHeader :: NCGConfig -> SectionType -> CLabel -> HLine #-} -- see Note [SPECIALIZE to HDoc] in GHC.Utils.Outputable +-- | Note [Split sections on COFF objects] +-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +-- +-- On Windows/COFF, LLD's gc-sections only works on COMDAT sections, +-- so we mark split sections as COMDAT and need to provide a unique +-- "key" symbol. +-- +-- Important: We must not use a dot-prefixed local label (e.g. +-- @.L...@) as the COMDAT key symbol, because LLVM's COFF assembler +-- treats dot-prefixed COMDAT key symbols specially and forces them to +-- have value 0 (the beginning of the section). That breaks +-- @tablesNextToCode@, where the info label is intentionally placed +-- after the info table data (at a non-zero offset). +-- +-- Therefore we generate a non-dot-prefixed key symbol derived from +-- the section suffix, and (see arch-specific 'pprSectionAlign') we +-- emit a label definition for it at the beginning of the section. +-- +-- ctor/dtor sections are specially treated; they must be emitted as +-- regular data sections, otherwise LLD will drop them. +-- +-- Note that we must not emit .equiv directives for COMDAT sections in +-- COFF objects, they seriously confuse LLD and we end up with access +-- violations at runtimes. +pprCOFFComdatKey :: IsLine doc => Platform -> CLabel -> doc +pprCOFFComdatKey platform suffix = + text "__ghc_coff_comdat_" <> pprAsmLabel platform suffix +{-# SPECIALIZE pprCOFFComdatKey :: Platform -> CLabel -> SDoc #-} +{-# SPECIALIZE pprCOFFComdatKey :: Platform -> CLabel -> HLine #-} -- see Note [SPECIALIZE to HDoc] in GHC.Utils.Outputable + -- XCOFF doesn't support relocating label-differences, so we place all -- RO sections into .text[PR] sections pprXcoffSectionHeader :: IsLine doc => SectionType -> doc ===================================== compiler/GHC/CmmToAsm/Wasm/FromCmm.hs ===================================== @@ -107,7 +107,7 @@ symKindFromCLabel lbl -- | Calculate a data section's kind, see haddock docs of -- 'DataSectionKind' for more explanation. dataSectionKindFromCmmSection :: Section -> DataSectionKind -dataSectionKindFromCmmSection s = case sectionProtection s of +dataSectionKindFromCmmSection (Section t _) = case sectionProtection t of ReadWriteSection -> SectionData _ -> SectionROData ===================================== compiler/GHC/CmmToAsm/X86/Ppr.hs ===================================== @@ -31,6 +31,7 @@ import GHC.Cmm hiding (topInfoTable) import GHC.Cmm.Dataflow.Label import GHC.Cmm.BlockId import GHC.Cmm.CLabel +import GHC.Cmm.InitFini import GHC.Cmm.DebugBlock (pprUnwindTable) import GHC.Types.Basic (Alignment, mkAlignment, alignmentBytes) @@ -195,8 +196,12 @@ pprDatas config (_, CmmStaticsRaw alias [CmmStaticLit (CmmLabel lbl), CmmStaticL labelInd _ = Nothing , Just ind' <- labelInd ind , alias `mayRedirectTo` ind' + -- See Note [Split sections on COFF objects] + , not $ platformOS platform == OSMinGW32 && ncgSplitSections config = pprGloblDecl (ncgPlatform config) alias $$ line (text ".equiv" <+> pprAsmLabel (ncgPlatform config) alias <> comma <> pprAsmLabel (ncgPlatform config) ind') + where + platform = ncgPlatform config pprDatas config (align, (CmmStaticsRaw lbl dats)) = vcat (pprAlign platform align : pprLabel platform lbl : map (pprData config) dats) @@ -526,9 +531,20 @@ pprAddr platform (AddrBaseIndex base index displacement) -- | Print section header and appropriate alignment for that section. pprSectionAlign :: IsDoc doc => NCGConfig -> Section -> doc -pprSectionAlign config sec@(Section seg _) = +pprSectionAlign config sec@(Section seg suffix) = line (pprSectionHeader config sec) $$ + coffSplitSectionComdatKey $$ pprAlignForSection (ncgPlatform config) seg + where + platform = ncgPlatform config + -- See Note [Split sections on COFF objects] + coffSplitSectionComdatKey + | OSMinGW32 <- platformOS platform + , ncgSplitSections config + , Nothing <- isInitOrFiniSection seg + = line (pprCOFFComdatKey platform suffix <> colon) + | otherwise + = empty -- | Print appropriate alignment for the given section type. pprAlignForSection :: IsDoc doc => Platform -> SectionType -> doc ===================================== compiler/GHC/CmmToC.hs ===================================== @@ -121,7 +121,7 @@ pprTop platform = \case pprDataExterns platform lits $$ pprWordArray platform (isSecConstant section) lbl lits where - isSecConstant section = case sectionProtection section of + isSecConstant (Section t _) = case sectionProtection t of ReadOnlySection -> True WriteProtectedSection -> True _ -> False ===================================== compiler/GHC/CmmToLlvm/Data.hs ===================================== @@ -75,7 +75,7 @@ genLlvmData (sect, statics) IsFiniArray -> fsLit "llvm.global_dtors" in genGlobalLabelArray var clbls -genLlvmData (sec, CmmStaticsRaw lbl xs) = do +genLlvmData (sec@(Section t _), CmmStaticsRaw lbl xs) = do label <- strCLabel_llvm lbl static <- mapM genData xs lmsec <- llvmSection sec @@ -92,7 +92,7 @@ genLlvmData (sec, CmmStaticsRaw lbl xs) = do then Just 2 else Just 1 Section Data _ -> Just $ platformWordSizeInBytes platform _ -> Nothing - const = if sectionProtection sec == ReadOnlySection + const = if sectionProtection t == ReadOnlySection then Constant else Global varDef = LMGlobalVar label tyAlias link lmsec align const globDef = LMGlobal varDef struct View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/641ec3f01974dff9dfd756f3f049979... -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/641ec3f01974dff9dfd756f3f049979... 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