MC: Fix fragment-in-BSS check #149721

MaskRay · 2025-07-20T16:44:13Z

Handle non-zero fill values for .fill and .org directives.
Restore the fragment type check
(5ee34ff removed a reachable
llvm_unreachable) to detect unintended API usage.

Remove virtual functions getVirtualSectionKind (added in
https://reviews.llvm.org/D78138) as they are unnecessary in diagnostics.
The a.out object file format has the BSS concept, which has been
inherited by COFF, XCOFF, Mach-O, and ELF object file formats.

Created using spr 1.3.5-bogner

llvmbot · 2025-07-20T16:44:47Z

@llvm/pr-subscribers-mc

@llvm/pr-subscribers-backend-arm

Author: Fangrui Song (MaskRay)

Changes

Replace getOrCreateDataFragment with getCurrentFragment, adding an assert to ensure CurFrag is either null or an FT_Data fragment.

Fix fragment-in-BSS check to handle non-zero fill values for .fill and .org directives.
Restore the fragment type check
(5ee34ff removed a reachable llvm_unreachable) to detect unintended API usage.

Remove virtual functions getVirtualSectionKind (added in
https://reviews.llvm.org/D78138) as they are unnecessary in diagnostics.
The a.out object file format has the BSS concept, which has been
inherited by COFF, XCOFF, Mach-O, and ELF object file formats.

The two changes are unrelated. Will land them separately.

Patch is 20.15 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/149721.diff

18 Files Affected:

(modified) llvm/include/llvm/MC/MCObjectStreamer.h (-3)
(modified) llvm/include/llvm/MC/MCSection.h (-2)
(modified) llvm/include/llvm/MC/MCSectionCOFF.h (-1)
(modified) llvm/include/llvm/MC/MCSectionELF.h (-1)
(modified) llvm/include/llvm/MC/MCStreamer.h (+4)
(modified) llvm/lib/MC/MCAssembler.cpp (+27-5)
(modified) llvm/lib/MC/MCObjectStreamer.cpp (+9-9)
(modified) llvm/lib/MC/MCParser/AsmParser.cpp (+2-3)
(modified) llvm/lib/MC/MCSection.cpp (-2)
(modified) llvm/lib/MC/MCSectionCOFF.cpp (-4)
(modified) llvm/lib/MC/MCSectionELF.cpp (-2)
(modified) llvm/lib/MC/MCWin64EH.cpp (+1-1)
(modified) llvm/lib/MC/MCWinCOFFStreamer.cpp (+5-5)
(modified) llvm/lib/MC/MCXCOFFStreamer.cpp (+1-1)
(modified) llvm/lib/Target/ARM/MCTargetDesc/ARMELFStreamer.cpp (+3-3)
(modified) llvm/lib/Target/Mips/MCTargetDesc/MipsTargetStreamer.cpp (+6-6)
(modified) llvm/test/MC/COFF/bss-text.s (+2-2)
(modified) llvm/test/MC/ELF/nobits-non-zero-value.s (+24-7)

diff --git a/llvm/include/llvm/MC/MCObjectStreamer.h b/llvm/include/llvm/MC/MCObjectStreamer.h
index 633334ee8a33f..429a1bb3321f6 100644
--- a/llvm/include/llvm/MC/MCObjectStreamer.h
+++ b/llvm/include/llvm/MC/MCObjectStreamer.h
@@ -72,9 +72,6 @@ class MCObjectStreamer : public MCStreamer {
   MCSymbol *emitCFILabel() override;
   void emitCFISections(bool EH, bool Debug) override;
 
-  // TODO: Change callers to use getCurrentFragment instead.
-  MCFragment *getOrCreateDataFragment() { return getCurrentFragment(); }
-
 protected:
   bool changeSectionImpl(MCSection *Section, uint32_t Subsection);
 
diff --git a/llvm/include/llvm/MC/MCSection.h b/llvm/include/llvm/MC/MCSection.h
index fe8c13d108c2c..72751f08e497b 100644
--- a/llvm/include/llvm/MC/MCSection.h
+++ b/llvm/include/llvm/MC/MCSection.h
@@ -179,8 +179,6 @@ class LLVM_ABI MCSection {
   /// Check whether this section is "virtual", that is has no actual object
   /// file contents.
   bool isVirtualSection() const { return IsVirtual; }
-
-  virtual StringRef getVirtualSectionKind() const;
 };
 
 // Represents a contiguous piece of code or data within a section. Its size is
diff --git a/llvm/include/llvm/MC/MCSectionCOFF.h b/llvm/include/llvm/MC/MCSectionCOFF.h
index 4472a128caa6b..f979413a3791e 100644
--- a/llvm/include/llvm/MC/MCSectionCOFF.h
+++ b/llvm/include/llvm/MC/MCSectionCOFF.h
@@ -82,7 +82,6 @@ class MCSectionCOFF final : public MCSection {
                             raw_ostream &OS,
                             uint32_t Subsection) const override;
   bool useCodeAlign() const override;
-  StringRef getVirtualSectionKind() const override;
 
   unsigned getOrAssignWinCFISectionID(unsigned *NextID) const {
     if (WinCFISectionID == ~0U)
diff --git a/llvm/include/llvm/MC/MCSectionELF.h b/llvm/include/llvm/MC/MCSectionELF.h
index f09d30591a3cf..a01f95f44c954 100644
--- a/llvm/include/llvm/MC/MCSectionELF.h
+++ b/llvm/include/llvm/MC/MCSectionELF.h
@@ -88,7 +88,6 @@ class MCSectionELF final : public MCSection {
                             raw_ostream &OS,
                             uint32_t Subsection) const override;
   bool useCodeAlign() const override;
-  StringRef getVirtualSectionKind() const override;
 
   bool isUnique() const { return UniqueID != NonUniqueID; }
   unsigned getUniqueID() const { return UniqueID; }
diff --git a/llvm/include/llvm/MC/MCStreamer.h b/llvm/include/llvm/MC/MCStreamer.h
index 0f87cf8f13a59..07566707424f9 100644
--- a/llvm/include/llvm/MC/MCStreamer.h
+++ b/llvm/include/llvm/MC/MCStreamer.h
@@ -427,8 +427,12 @@ class LLVM_ABI MCStreamer {
   }
 
   MCFragment *getCurrentFragment() const {
+    // Ensure consistency with the section stack.
     assert(!getCurrentSection().first ||
            CurFrag->getParent() == getCurrentSection().first);
+    // Ensure we eagerly allocate an empty fragment when adding fragment with a
+    // variable-size tail.
+    assert(!CurFrag || CurFrag->getKind() == MCFragment::FT_Data);
     return CurFrag;
   }
   /// Save the current and previous section on the section stack.
diff --git a/llvm/lib/MC/MCAssembler.cpp b/llvm/lib/MC/MCAssembler.cpp
index 674adc92257c9..9943d56d2deaa 100644
--- a/llvm/lib/MC/MCAssembler.cpp
+++ b/llvm/lib/MC/MCAssembler.cpp
@@ -567,15 +567,37 @@ void MCAssembler::writeSectionData(raw_ostream &OS,
     // not tracked for efficiency.
     auto Fn = [](char c) { return c != 0; };
     for (const MCFragment &F : *Sec) {
-      if (any_of(F.getContents(), Fn) || any_of(F.getVarContents(), Fn)) {
-        reportError(SMLoc(), Sec->getVirtualSectionKind() + " section '" +
-                                 Sec->getName() +
+      bool HasNonZero = false;
+      switch (F.getKind()) {
+      default:
+        reportFatalInternalError("BSS section '" + Sec->getName() +
+                                 "' contains invalid fragment");
+        break;
+      case MCFragment::FT_Data:
+      case MCFragment::FT_Relaxable:
+        HasNonZero =
+            any_of(F.getContents(), Fn) || any_of(F.getVarContents(), Fn);
+        break;
+      case MCFragment::FT_Align:
+        // Disallowed for API usage. AsmParser changes non-zero fill values to
+        // 0.
+        assert(F.getAlignFill() == 0 && "Invalid align in virtual section!");
+        break;
+      case MCFragment::FT_Fill:
+        HasNonZero = cast<MCFillFragment>(F).getValue() != 0;
+        break;
+      case MCFragment::FT_Org:
+        HasNonZero = cast<MCOrgFragment>(F).getValue() != 0;
+        break;
+      }
+      if (HasNonZero) {
+        reportError(SMLoc(), "BSS section '" + Sec->getName() +
                                  "' cannot have non-zero bytes");
         break;
       }
       if (F.getFixups().size() || F.getVarFixups().size()) {
-        reportError(SMLoc(), Sec->getVirtualSectionKind() + " section '" +
-                                 Sec->getName() + "' cannot have fixups");
+        reportError(SMLoc(),
+                    "BSS section '" + Sec->getName() + "' cannot have fixups");
         break;
       }
     }
diff --git a/llvm/lib/MC/MCObjectStreamer.cpp b/llvm/lib/MC/MCObjectStreamer.cpp
index 83e447abb7e06..4c99010700fc7 100644
--- a/llvm/lib/MC/MCObjectStreamer.cpp
+++ b/llvm/lib/MC/MCObjectStreamer.cpp
@@ -119,7 +119,7 @@ void MCObjectStreamer::emitCFISections(bool EH, bool Debug) {
 void MCObjectStreamer::emitValueImpl(const MCExpr *Value, unsigned Size,
                                      SMLoc Loc) {
   MCStreamer::emitValueImpl(Value, Size, Loc);
-  MCFragment *DF = getOrCreateDataFragment();
+  MCFragment *DF = getCurrentFragment();
 
   MCDwarfLineEntry::make(this, getCurrentSectionOnly());
 
@@ -168,7 +168,7 @@ void MCObjectStreamer::emitLabel(MCSymbol *Symbol, SMLoc Loc) {
   // If there is a current fragment, mark the symbol as pointing into it.
   // Otherwise queue the label and set its fragment pointer when we emit the
   // next fragment.
-  MCFragment *F = getOrCreateDataFragment();
+  MCFragment *F = getCurrentFragment();
   Symbol->setFragment(F);
   Symbol->setOffset(F->getContents().size());
 
@@ -202,7 +202,7 @@ void MCObjectStreamer::emitULEB128Value(const MCExpr *Value) {
     emitULEB128IntValue(IntValue);
     return;
   }
-  auto *F = getOrCreateDataFragment();
+  auto *F = getCurrentFragment();
   F->makeLEB(false, Value);
   newFragment();
 }
@@ -213,7 +213,7 @@ void MCObjectStreamer::emitSLEB128Value(const MCExpr *Value) {
     emitSLEB128IntValue(IntValue);
     return;
   }
-  auto *F = getOrCreateDataFragment();
+  auto *F = getCurrentFragment();
   F->makeLEB(true, Value);
   newFragment();
 }
@@ -312,7 +312,7 @@ void MCObjectStreamer::emitInstruction(const MCInst &Inst,
 
 void MCObjectStreamer::emitInstToData(const MCInst &Inst,
                                       const MCSubtargetInfo &STI) {
-  MCFragment *F = getOrCreateDataFragment();
+  MCFragment *F = getCurrentFragment();
 
   // Append the instruction to the data fragment.
   size_t FixupStartIndex = F->getFixups().size();
@@ -344,7 +344,7 @@ void MCObjectStreamer::emitInstToData(const MCInst &Inst,
 
 void MCObjectStreamer::emitInstToFragment(const MCInst &Inst,
                                           const MCSubtargetInfo &STI) {
-  auto *F = getOrCreateDataFragment();
+  auto *F = getCurrentFragment();
   SmallVector<char, 16> Data;
   SmallVector<MCFixup, 1> Fixups;
   getAssembler().getEmitter().encodeInstruction(Inst, Data, Fixups, STI);
@@ -417,7 +417,7 @@ void MCObjectStreamer::emitDwarfAdvanceLineAddr(int64_t LineDelta,
     return;
   }
 
-  auto *F = getOrCreateDataFragment();
+  auto *F = getCurrentFragment();
   F->Kind = MCFragment::FT_Dwarf;
   F->setDwarfAddrDelta(buildSymbolDiff(*this, Label, LastLabel, SMLoc()));
   F->setDwarfLineDelta(LineDelta);
@@ -449,7 +449,7 @@ void MCObjectStreamer::emitDwarfLineEndEntry(MCSection *Section,
 void MCObjectStreamer::emitDwarfAdvanceFrameAddr(const MCSymbol *LastLabel,
                                                  const MCSymbol *Label,
                                                  SMLoc Loc) {
-  auto *F = getOrCreateDataFragment();
+  auto *F = getCurrentFragment();
   F->Kind = MCFragment::FT_DwarfFrame;
   F->setDwarfAddrDelta(buildSymbolDiff(*this, Label, LastLabel, Loc));
   newFragment();
@@ -511,7 +511,7 @@ void MCObjectStreamer::emitCVFileChecksumOffsetDirective(unsigned FileNo) {
 
 void MCObjectStreamer::emitBytes(StringRef Data) {
   MCDwarfLineEntry::make(this, getCurrentSectionOnly());
-  MCFragment *DF = getOrCreateDataFragment();
+  MCFragment *DF = getCurrentFragment();
   DF->appendContents(ArrayRef(Data.data(), Data.size()));
 }
 
diff --git a/llvm/lib/MC/MCParser/AsmParser.cpp b/llvm/lib/MC/MCParser/AsmParser.cpp
index 77bf84364c5a3..6f07bd553bba0 100644
--- a/llvm/lib/MC/MCParser/AsmParser.cpp
+++ b/llvm/lib/MC/MCParser/AsmParser.cpp
@@ -3406,9 +3406,8 @@ bool AsmParser::parseDirectiveAlign(bool IsPow2, uint8_t ValueSize) {
 
   if (HasFillExpr && FillExpr != 0 && Section->isVirtualSection()) {
     ReturnVal |=
-        Warning(FillExprLoc, "ignoring non-zero fill value in " +
-                                 Section->getVirtualSectionKind() +
-                                 " section '" + Section->getName() + "'");
+        Warning(FillExprLoc, "ignoring non-zero fill value in BSS section '" +
+                                 Section->getName() + "'");
     FillExpr = 0;
   }
 
diff --git a/llvm/lib/MC/MCSection.cpp b/llvm/lib/MC/MCSection.cpp
index 93671450c0c2f..251412d99efbf 100644
--- a/llvm/lib/MC/MCSection.cpp
+++ b/llvm/lib/MC/MCSection.cpp
@@ -34,8 +34,6 @@ MCSymbol *MCSection::getEndSymbol(MCContext &Ctx) {
 
 bool MCSection::hasEnded() const { return End && End->isInSection(); }
 
-StringRef MCSection::getVirtualSectionKind() const { return "virtual"; }
-
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
 LLVM_DUMP_METHOD void MCSection::dump(
     DenseMap<const MCFragment *, SmallVector<const MCSymbol *, 0>> *FragToSyms)
diff --git a/llvm/lib/MC/MCSectionCOFF.cpp b/llvm/lib/MC/MCSectionCOFF.cpp
index 94e29ce27d881..5bf14735eda9b 100644
--- a/llvm/lib/MC/MCSectionCOFF.cpp
+++ b/llvm/lib/MC/MCSectionCOFF.cpp
@@ -115,7 +115,3 @@ void MCSectionCOFF::printSwitchToSection(const MCAsmInfo &MAI, const Triple &T,
 }
 
 bool MCSectionCOFF::useCodeAlign() const { return isText(); }
-
-StringRef MCSectionCOFF::getVirtualSectionKind() const {
-  return "IMAGE_SCN_CNT_UNINITIALIZED_DATA";
-}
diff --git a/llvm/lib/MC/MCSectionELF.cpp b/llvm/lib/MC/MCSectionELF.cpp
index 299fe40706e3a..ef33f9c314579 100644
--- a/llvm/lib/MC/MCSectionELF.cpp
+++ b/llvm/lib/MC/MCSectionELF.cpp
@@ -215,5 +215,3 @@ void MCSectionELF::printSwitchToSection(const MCAsmInfo &MAI, const Triple &T,
 bool MCSectionELF::useCodeAlign() const {
   return getFlags() & ELF::SHF_EXECINSTR;
 }
-
-StringRef MCSectionELF::getVirtualSectionKind() const { return "SHT_NOBITS"; }
diff --git a/llvm/lib/MC/MCWin64EH.cpp b/llvm/lib/MC/MCWin64EH.cpp
index e8b26bf291ee4..a1c049aaed9cb 100644
--- a/llvm/lib/MC/MCWin64EH.cpp
+++ b/llvm/lib/MC/MCWin64EH.cpp
@@ -318,7 +318,7 @@ static void EmitUnwindInfo(MCStreamer &streamer, WinEH::FrameInfo *info) {
 
   // Emit the epilog instructions.
   if (EnableUnwindV2) {
-    MCFragment *DF = OS->getOrCreateDataFragment();
+    MCFragment *DF = OS->getCurrentFragment();
 
     bool IsLast = true;
     for (const auto &Epilog : llvm::reverse(info->EpilogMap)) {
diff --git a/llvm/lib/MC/MCWinCOFFStreamer.cpp b/llvm/lib/MC/MCWinCOFFStreamer.cpp
index 3398775df3f91..370280eb87cfd 100644
--- a/llvm/lib/MC/MCWinCOFFStreamer.cpp
+++ b/llvm/lib/MC/MCWinCOFFStreamer.cpp
@@ -278,7 +278,7 @@ void MCWinCOFFStreamer::emitCOFFSymbolIndex(MCSymbol const *Symbol) {
 
 void MCWinCOFFStreamer::emitCOFFSectionIndex(const MCSymbol *Symbol) {
   visitUsedSymbol(*Symbol);
-  MCFragment *DF = getOrCreateDataFragment();
+  MCFragment *DF = getCurrentFragment();
   const MCSymbolRefExpr *SRE = MCSymbolRefExpr::create(Symbol, getContext());
   MCFixup Fixup = MCFixup::create(DF->getContents().size(), SRE, FK_SecRel_2);
   DF->addFixup(Fixup);
@@ -288,7 +288,7 @@ void MCWinCOFFStreamer::emitCOFFSectionIndex(const MCSymbol *Symbol) {
 void MCWinCOFFStreamer::emitCOFFSecRel32(const MCSymbol *Symbol,
                                          uint64_t Offset) {
   visitUsedSymbol(*Symbol);
-  MCFragment *DF = getOrCreateDataFragment();
+  MCFragment *DF = getCurrentFragment();
   // Create Symbol A for the relocation relative reference.
   const MCExpr *MCE = MCSymbolRefExpr::create(Symbol, getContext());
   // Add the constant offset, if given.
@@ -306,7 +306,7 @@ void MCWinCOFFStreamer::emitCOFFSecRel32(const MCSymbol *Symbol,
 void MCWinCOFFStreamer::emitCOFFImgRel32(const MCSymbol *Symbol,
                                          int64_t Offset) {
   visitUsedSymbol(*Symbol);
-  MCFragment *DF = getOrCreateDataFragment();
+  MCFragment *DF = getCurrentFragment();
   // Create Symbol A for the relocation relative reference.
   const MCExpr *MCE = MCSymbolRefExpr::create(
       Symbol, MCSymbolRefExpr::VK_COFF_IMGREL32, getContext());
@@ -324,7 +324,7 @@ void MCWinCOFFStreamer::emitCOFFImgRel32(const MCSymbol *Symbol,
 
 void MCWinCOFFStreamer::emitCOFFSecNumber(MCSymbol const *Symbol) {
   visitUsedSymbol(*Symbol);
-  MCFragment *DF = getOrCreateDataFragment();
+  MCFragment *DF = getCurrentFragment();
   // Create Symbol for section number.
   const MCExpr *MCE = MCCOFFSectionNumberTargetExpr::create(
       *Symbol, this->getWriter(), getContext());
@@ -338,7 +338,7 @@ void MCWinCOFFStreamer::emitCOFFSecNumber(MCSymbol const *Symbol) {
 
 void MCWinCOFFStreamer::emitCOFFSecOffset(MCSymbol const *Symbol) {
   visitUsedSymbol(*Symbol);
-  MCFragment *DF = getOrCreateDataFragment();
+  MCFragment *DF = getCurrentFragment();
   // Create Symbol for section offset.
   const MCExpr *MCE =
       MCCOFFSectionOffsetTargetExpr::create(*Symbol, getContext());
diff --git a/llvm/lib/MC/MCXCOFFStreamer.cpp b/llvm/lib/MC/MCXCOFFStreamer.cpp
index 4d4529653aba9..63381b4f81859 100644
--- a/llvm/lib/MC/MCXCOFFStreamer.cpp
+++ b/llvm/lib/MC/MCXCOFFStreamer.cpp
@@ -89,7 +89,7 @@ void MCXCOFFStreamer::emitXCOFFSymbolLinkageWithVisibility(
 void MCXCOFFStreamer::emitXCOFFRefDirective(const MCSymbol *Symbol) {
   // Add a Fixup here to later record a relocation of type R_REF to prevent the
   // ref symbol from being garbage collected (by the binder).
-  MCFragment *DF = getOrCreateDataFragment();
+  MCFragment *DF = getCurrentFragment();
   const MCSymbolRefExpr *SRE = MCSymbolRefExpr::create(Symbol, getContext());
   std::optional<MCFixupKind> MaybeKind =
       getAssembler().getBackend().getFixupKind("R_REF");
diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMELFStreamer.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMELFStreamer.cpp
index eaba6fe5bfcb7..a7a9911de2d04 100644
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMELFStreamer.cpp
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMELFStreamer.cpp
@@ -593,7 +593,7 @@ class ARMELFStreamer : public MCELFStreamer {
         getContext().reportError(Loc, "relocated expression must be 32-bit");
         return;
       }
-      getOrCreateDataFragment();
+      getCurrentFragment();
     }
 
     emitDataMappingSymbol();
@@ -1207,7 +1207,7 @@ inline void ARMELFStreamer::SwitchToExIdxSection(const MCSymbol &FnStart) {
 }
 
 void ARMELFStreamer::EmitFixup(const MCExpr *Expr, MCFixupKind Kind) {
-  MCFragment *Frag = getOrCreateDataFragment();
+  MCFragment *Frag = getCurrentFragment();
   Frag->addFixup(MCFixup::create(Frag->getContents().size(), Expr, Kind));
 }
 
@@ -1295,7 +1295,7 @@ void ARMELFStreamer::EmitPersonalityFixup(StringRef Name) {
       MCSymbolRefExpr::create(PersonalitySym, ARM::S_ARM_NONE, getContext());
 
   visitUsedExpr(*PersonalityRef);
-  MCFragment *DF = getOrCreateDataFragment();
+  MCFragment *DF = getCurrentFragment();
   DF->addFixup(
       MCFixup::create(DF->getContents().size(), PersonalityRef, FK_Data_4));
 }
diff --git a/llvm/lib/Target/Mips/MCTargetDesc/MipsTargetStreamer.cpp b/llvm/lib/Target/Mips/MCTargetDesc/MipsTargetStreamer.cpp
index b89d6890903dd..5c7f34b870847 100644
--- a/llvm/lib/Target/Mips/MCTargetDesc/MipsTargetStreamer.cpp
+++ b/llvm/lib/Target/Mips/MCTargetDesc/MipsTargetStreamer.cpp
@@ -1033,42 +1033,42 @@ MCELFStreamer &MipsTargetELFStreamer::getStreamer() {
 }
 
 void MipsTargetELFStreamer::emitGPRel32Value(const MCExpr *Value) {
-  MCFragment *DF = getStreamer().getOrCreateDataFragment();
+  MCFragment *DF = getStreamer().getCurrentFragment();
   DF->addFixup(MCFixup::create(DF->getContents().size(), Value,
                                Mips::fixup_Mips_GPREL32));
   DF->appendContents(4, 0);
 }
 
 void MipsTargetELFStreamer::emitGPRel64Value(const MCExpr *Value) {
-  MCFragment *DF = getStreamer().getOrCreateDataFragment();
+  MCFragment *DF = getStreamer().getCurrentFragment();
   DF->addFixup(MCFixup::create(DF->getContents().size(), Value,
                                Mips::fixup_Mips_GPREL32));
   DF->appendContents(8, 0);
 }
 
 void MipsTargetELFStreamer::emitDTPRel32Value(const MCExpr *Value) {
-  MCFragment *DF = getStreamer().getOrCreateDataFragment();
+  MCFragment *DF = getStreamer().getCurrentFragment();
   DF->addFixup(MCFixup::create(DF->getContents().size(), Value,
                                Mips::fixup_Mips_DTPREL32));
   DF->appendContents(4, 0);
 }
 
 void MipsTargetELFStreamer::emitDTPRel64Value(const MCExpr *Value) {
-  MCFragment *DF = getStreamer().getOrCreateDataFragment();
+  MCFragment *DF = getStreamer().getCurrentFragment();
   DF->addFixup(MCFixup::create(DF->getContents().size(), Value,
                                Mips::fixup_Mips_DTPREL64));
   DF->appendContents(8, 0);
 }
 
 void MipsTargetELFStreamer::emitTPRel32Value(const MCExpr *Value) {
-  MCFragment *DF = getStreamer().getOrCreateDataFragment();
+  MCFragment *DF = getStreamer().getCurrentFragment();
   DF->addFixup(MCFixup::create(DF->getContents().size(), Value,
                                Mips::fixup_Mips_TPREL32));
   DF->appendContents(4, 0);
 }
 
 void MipsTargetELFStreamer::emitTPRel64Value(const MCExpr *Value) {
-  MCFragment *DF = getStreamer().getOrCreateDataFragment();
+  MCFragment *DF = getStreamer().getCurrentFragment();
   DF->addFixup(MCFixup::create(DF->getContents().size(), Value,
                                Mips::fixup_Mips_TPREL64));
   DF->appendContents(8, 0);
diff --git a/llvm/test/MC/COFF/bss-text.s b/llvm/test/MC/COFF/bss-text.s
index 439bd789dff2c..cedbb2f032236 100644
--- a/llvm/test/MC/COFF/bss-text.s
+++ b/llvm/test/MC/COFF/bss-text.s
@@ -4,11 +4,11 @@
 # RUN: llvm-mc -triple=x86_64-pc-win32 %s
 
 .bss
-# CHECK: <unknown>:0: error: IMAGE_SCN_CNT_UNINITIALIZED_DATA section '.bss' cannot have non-zero bytes
+# CHECK: <unknown>:0: error: BSS section '.bss' cannot have non-zero bytes
   addb %bl,(%rax)
 
 .section uninitialized,"b"
-# CHECK: <unknown>:0: error: IMAGE_SCN_CNT_UNINITIALIZED_DATA section 'uninitialized' cannot have non-zero bytes
+# CHECK: <unknown>:0: error: BSS section 'uninitialized' cannot have non-zero bytes
   jmp foo
 
 .section bss0,"b"
diff --git a/llvm/test/MC/ELF/nobits-non-zero-value.s b/llvm/test/MC/ELF/nobits-non-zero-value.s
index e9516aa3e835a..ea95ec97ac8d2 100644
--- a/llvm/test/MC/ELF/nobits-non-zero-value.s
+++ b/llvm/test/MC/ELF/nobits-non-zero-value.s
@@ -9,20 +9,37 @@
 .bss
   addb %al,(%rax)
 
-# CHECK: {{.*}}.s:[[#@LINE+1]]:11: warning: ignoring non-zero fill value in SHT_NOBITS section '.bss'
+# CHECK: {{.*}}.s:[[#@LINE+1]]:11: warning: ignoring non-zero fill value in BSS section '.bss'
 .align 4, 42
 
-.align 4, 0
-
   .long 1
 
 .section .bss0,"aw",%nobits
 addb %al,(%rax)
 
-.section .bss1,"aw",%nobits
+.section data_fixup,"aw",%nobits
 .quad foo
 
+.section fill,"aw",%nobits
+.fill b-a,1,1
+
+.section org,"aw",%nobits
+.org 1,1
+
+.section ok,"aw",%nobits
+.org 1
+.fill 1
+.fill b-a,1,0
+.align 4, 0
+.long 0
+
+.text
+a: nop
+b:
+
 ## Location is not tracked for efficiency.
-# CHECK: <unknown>:0: error: SHT_NOBITS section '.tbss' cannot have non-zero bytes
-# CHECK: <unknown>:0: error: SHT_NOBITS section '.bss' cannot have non-zero bytes
-# CHECK: <unknown>:0: error: SHT_NOBITS section '.bss1' cannot have fixups
+# CHECK: <unknown>:0: error: BSS section '.tbss' cannot have non-zero bytes
+# CHECK: <unknown>:0: error: BSS section '.bss' cannot have non-zero bytes
+# CHECK: <unknown>:0: error: BSS section 'data_fixup' cannot have fixups
+#...
[truncated]

llvmbot · 2025-07-20T16:44:47Z

@llvm/pr-subscribers-backend-mips

Author: Fangrui Song (MaskRay)

Changes

Replace getOrCreateDataFragment with getCurrentFragment, adding an assert to ensure CurFrag is either null or an FT_Data fragment.

Fix fragment-in-BSS check to handle non-zero fill values for .fill and .org directives.
Restore the fragment type check
(5ee34ff removed a reachable llvm_unreachable) to detect unintended API usage.

Remove virtual functions getVirtualSectionKind (added in
https://reviews.llvm.org/D78138) as they are unnecessary in diagnostics.
The a.out object file format has the BSS concept, which has been
inherited by COFF, XCOFF, Mach-O, and ELF object file formats.

The two changes are unrelated. Will land them separately.

Patch is 20.15 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/149721.diff

18 Files Affected:

(modified) llvm/include/llvm/MC/MCObjectStreamer.h (-3)
(modified) llvm/include/llvm/MC/MCSection.h (-2)
(modified) llvm/include/llvm/MC/MCSectionCOFF.h (-1)
(modified) llvm/include/llvm/MC/MCSectionELF.h (-1)
(modified) llvm/include/llvm/MC/MCStreamer.h (+4)
(modified) llvm/lib/MC/MCAssembler.cpp (+27-5)
(modified) llvm/lib/MC/MCObjectStreamer.cpp (+9-9)
(modified) llvm/lib/MC/MCParser/AsmParser.cpp (+2-3)
(modified) llvm/lib/MC/MCSection.cpp (-2)
(modified) llvm/lib/MC/MCSectionCOFF.cpp (-4)
(modified) llvm/lib/MC/MCSectionELF.cpp (-2)
(modified) llvm/lib/MC/MCWin64EH.cpp (+1-1)
(modified) llvm/lib/MC/MCWinCOFFStreamer.cpp (+5-5)
(modified) llvm/lib/MC/MCXCOFFStreamer.cpp (+1-1)
(modified) llvm/lib/Target/ARM/MCTargetDesc/ARMELFStreamer.cpp (+3-3)
(modified) llvm/lib/Target/Mips/MCTargetDesc/MipsTargetStreamer.cpp (+6-6)
(modified) llvm/test/MC/COFF/bss-text.s (+2-2)
(modified) llvm/test/MC/ELF/nobits-non-zero-value.s (+24-7)

diff --git a/llvm/include/llvm/MC/MCObjectStreamer.h b/llvm/include/llvm/MC/MCObjectStreamer.h
index 633334ee8a33f..429a1bb3321f6 100644
--- a/llvm/include/llvm/MC/MCObjectStreamer.h
+++ b/llvm/include/llvm/MC/MCObjectStreamer.h
@@ -72,9 +72,6 @@ class MCObjectStreamer : public MCStreamer {
   MCSymbol *emitCFILabel() override;
   void emitCFISections(bool EH, bool Debug) override;
 
-  // TODO: Change callers to use getCurrentFragment instead.
-  MCFragment *getOrCreateDataFragment() { return getCurrentFragment(); }
-
 protected:
   bool changeSectionImpl(MCSection *Section, uint32_t Subsection);
 
diff --git a/llvm/include/llvm/MC/MCSection.h b/llvm/include/llvm/MC/MCSection.h
index fe8c13d108c2c..72751f08e497b 100644
--- a/llvm/include/llvm/MC/MCSection.h
+++ b/llvm/include/llvm/MC/MCSection.h
@@ -179,8 +179,6 @@ class LLVM_ABI MCSection {
   /// Check whether this section is "virtual", that is has no actual object
   /// file contents.
   bool isVirtualSection() const { return IsVirtual; }
-
-  virtual StringRef getVirtualSectionKind() const;
 };
 
 // Represents a contiguous piece of code or data within a section. Its size is
diff --git a/llvm/include/llvm/MC/MCSectionCOFF.h b/llvm/include/llvm/MC/MCSectionCOFF.h
index 4472a128caa6b..f979413a3791e 100644
--- a/llvm/include/llvm/MC/MCSectionCOFF.h
+++ b/llvm/include/llvm/MC/MCSectionCOFF.h
@@ -82,7 +82,6 @@ class MCSectionCOFF final : public MCSection {
                             raw_ostream &OS,
                             uint32_t Subsection) const override;
   bool useCodeAlign() const override;
-  StringRef getVirtualSectionKind() const override;
 
   unsigned getOrAssignWinCFISectionID(unsigned *NextID) const {
     if (WinCFISectionID == ~0U)
diff --git a/llvm/include/llvm/MC/MCSectionELF.h b/llvm/include/llvm/MC/MCSectionELF.h
index f09d30591a3cf..a01f95f44c954 100644
--- a/llvm/include/llvm/MC/MCSectionELF.h
+++ b/llvm/include/llvm/MC/MCSectionELF.h
@@ -88,7 +88,6 @@ class MCSectionELF final : public MCSection {
                             raw_ostream &OS,
                             uint32_t Subsection) const override;
   bool useCodeAlign() const override;
-  StringRef getVirtualSectionKind() const override;
 
   bool isUnique() const { return UniqueID != NonUniqueID; }
   unsigned getUniqueID() const { return UniqueID; }
diff --git a/llvm/include/llvm/MC/MCStreamer.h b/llvm/include/llvm/MC/MCStreamer.h
index 0f87cf8f13a59..07566707424f9 100644
--- a/llvm/include/llvm/MC/MCStreamer.h
+++ b/llvm/include/llvm/MC/MCStreamer.h
@@ -427,8 +427,12 @@ class LLVM_ABI MCStreamer {
   }
 
   MCFragment *getCurrentFragment() const {
+    // Ensure consistency with the section stack.
     assert(!getCurrentSection().first ||
            CurFrag->getParent() == getCurrentSection().first);
+    // Ensure we eagerly allocate an empty fragment when adding fragment with a
+    // variable-size tail.
+    assert(!CurFrag || CurFrag->getKind() == MCFragment::FT_Data);
     return CurFrag;
   }
   /// Save the current and previous section on the section stack.
diff --git a/llvm/lib/MC/MCAssembler.cpp b/llvm/lib/MC/MCAssembler.cpp
index 674adc92257c9..9943d56d2deaa 100644
--- a/llvm/lib/MC/MCAssembler.cpp
+++ b/llvm/lib/MC/MCAssembler.cpp
@@ -567,15 +567,37 @@ void MCAssembler::writeSectionData(raw_ostream &OS,
     // not tracked for efficiency.
     auto Fn = [](char c) { return c != 0; };
     for (const MCFragment &F : *Sec) {
-      if (any_of(F.getContents(), Fn) || any_of(F.getVarContents(), Fn)) {
-        reportError(SMLoc(), Sec->getVirtualSectionKind() + " section '" +
-                                 Sec->getName() +
+      bool HasNonZero = false;
+      switch (F.getKind()) {
+      default:
+        reportFatalInternalError("BSS section '" + Sec->getName() +
+                                 "' contains invalid fragment");
+        break;
+      case MCFragment::FT_Data:
+      case MCFragment::FT_Relaxable:
+        HasNonZero =
+            any_of(F.getContents(), Fn) || any_of(F.getVarContents(), Fn);
+        break;
+      case MCFragment::FT_Align:
+        // Disallowed for API usage. AsmParser changes non-zero fill values to
+        // 0.
+        assert(F.getAlignFill() == 0 && "Invalid align in virtual section!");
+        break;
+      case MCFragment::FT_Fill:
+        HasNonZero = cast<MCFillFragment>(F).getValue() != 0;
+        break;
+      case MCFragment::FT_Org:
+        HasNonZero = cast<MCOrgFragment>(F).getValue() != 0;
+        break;
+      }
+      if (HasNonZero) {
+        reportError(SMLoc(), "BSS section '" + Sec->getName() +
                                  "' cannot have non-zero bytes");
         break;
       }
       if (F.getFixups().size() || F.getVarFixups().size()) {
-        reportError(SMLoc(), Sec->getVirtualSectionKind() + " section '" +
-                                 Sec->getName() + "' cannot have fixups");
+        reportError(SMLoc(),
+                    "BSS section '" + Sec->getName() + "' cannot have fixups");
         break;
       }
     }
diff --git a/llvm/lib/MC/MCObjectStreamer.cpp b/llvm/lib/MC/MCObjectStreamer.cpp
index 83e447abb7e06..4c99010700fc7 100644
--- a/llvm/lib/MC/MCObjectStreamer.cpp
+++ b/llvm/lib/MC/MCObjectStreamer.cpp
@@ -119,7 +119,7 @@ void MCObjectStreamer::emitCFISections(bool EH, bool Debug) {
 void MCObjectStreamer::emitValueImpl(const MCExpr *Value, unsigned Size,
                                      SMLoc Loc) {
   MCStreamer::emitValueImpl(Value, Size, Loc);
-  MCFragment *DF = getOrCreateDataFragment();
+  MCFragment *DF = getCurrentFragment();
 
   MCDwarfLineEntry::make(this, getCurrentSectionOnly());
 
@@ -168,7 +168,7 @@ void MCObjectStreamer::emitLabel(MCSymbol *Symbol, SMLoc Loc) {
   // If there is a current fragment, mark the symbol as pointing into it.
   // Otherwise queue the label and set its fragment pointer when we emit the
   // next fragment.
-  MCFragment *F = getOrCreateDataFragment();
+  MCFragment *F = getCurrentFragment();
   Symbol->setFragment(F);
   Symbol->setOffset(F->getContents().size());
 
@@ -202,7 +202,7 @@ void MCObjectStreamer::emitULEB128Value(const MCExpr *Value) {
     emitULEB128IntValue(IntValue);
     return;
   }
-  auto *F = getOrCreateDataFragment();
+  auto *F = getCurrentFragment();
   F->makeLEB(false, Value);
   newFragment();
 }
@@ -213,7 +213,7 @@ void MCObjectStreamer::emitSLEB128Value(const MCExpr *Value) {
     emitSLEB128IntValue(IntValue);
     return;
   }
-  auto *F = getOrCreateDataFragment();
+  auto *F = getCurrentFragment();
   F->makeLEB(true, Value);
   newFragment();
 }
@@ -312,7 +312,7 @@ void MCObjectStreamer::emitInstruction(const MCInst &Inst,
 
 void MCObjectStreamer::emitInstToData(const MCInst &Inst,
                                       const MCSubtargetInfo &STI) {
-  MCFragment *F = getOrCreateDataFragment();
+  MCFragment *F = getCurrentFragment();
 
   // Append the instruction to the data fragment.
   size_t FixupStartIndex = F->getFixups().size();
@@ -344,7 +344,7 @@ void MCObjectStreamer::emitInstToData(const MCInst &Inst,
 
 void MCObjectStreamer::emitInstToFragment(const MCInst &Inst,
                                           const MCSubtargetInfo &STI) {
-  auto *F = getOrCreateDataFragment();
+  auto *F = getCurrentFragment();
   SmallVector<char, 16> Data;
   SmallVector<MCFixup, 1> Fixups;
   getAssembler().getEmitter().encodeInstruction(Inst, Data, Fixups, STI);
@@ -417,7 +417,7 @@ void MCObjectStreamer::emitDwarfAdvanceLineAddr(int64_t LineDelta,
     return;
   }
 
-  auto *F = getOrCreateDataFragment();
+  auto *F = getCurrentFragment();
   F->Kind = MCFragment::FT_Dwarf;
   F->setDwarfAddrDelta(buildSymbolDiff(*this, Label, LastLabel, SMLoc()));
   F->setDwarfLineDelta(LineDelta);
@@ -449,7 +449,7 @@ void MCObjectStreamer::emitDwarfLineEndEntry(MCSection *Section,
 void MCObjectStreamer::emitDwarfAdvanceFrameAddr(const MCSymbol *LastLabel,
                                                  const MCSymbol *Label,
                                                  SMLoc Loc) {
-  auto *F = getOrCreateDataFragment();
+  auto *F = getCurrentFragment();
   F->Kind = MCFragment::FT_DwarfFrame;
   F->setDwarfAddrDelta(buildSymbolDiff(*this, Label, LastLabel, Loc));
   newFragment();
@@ -511,7 +511,7 @@ void MCObjectStreamer::emitCVFileChecksumOffsetDirective(unsigned FileNo) {
 
 void MCObjectStreamer::emitBytes(StringRef Data) {
   MCDwarfLineEntry::make(this, getCurrentSectionOnly());
-  MCFragment *DF = getOrCreateDataFragment();
+  MCFragment *DF = getCurrentFragment();
   DF->appendContents(ArrayRef(Data.data(), Data.size()));
 }
 
diff --git a/llvm/lib/MC/MCParser/AsmParser.cpp b/llvm/lib/MC/MCParser/AsmParser.cpp
index 77bf84364c5a3..6f07bd553bba0 100644
--- a/llvm/lib/MC/MCParser/AsmParser.cpp
+++ b/llvm/lib/MC/MCParser/AsmParser.cpp
@@ -3406,9 +3406,8 @@ bool AsmParser::parseDirectiveAlign(bool IsPow2, uint8_t ValueSize) {
 
   if (HasFillExpr && FillExpr != 0 && Section->isVirtualSection()) {
     ReturnVal |=
-        Warning(FillExprLoc, "ignoring non-zero fill value in " +
-                                 Section->getVirtualSectionKind() +
-                                 " section '" + Section->getName() + "'");
+        Warning(FillExprLoc, "ignoring non-zero fill value in BSS section '" +
+                                 Section->getName() + "'");
     FillExpr = 0;
   }
 
diff --git a/llvm/lib/MC/MCSection.cpp b/llvm/lib/MC/MCSection.cpp
index 93671450c0c2f..251412d99efbf 100644
--- a/llvm/lib/MC/MCSection.cpp
+++ b/llvm/lib/MC/MCSection.cpp
@@ -34,8 +34,6 @@ MCSymbol *MCSection::getEndSymbol(MCContext &Ctx) {
 
 bool MCSection::hasEnded() const { return End && End->isInSection(); }
 
-StringRef MCSection::getVirtualSectionKind() const { return "virtual"; }
-
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
 LLVM_DUMP_METHOD void MCSection::dump(
     DenseMap<const MCFragment *, SmallVector<const MCSymbol *, 0>> *FragToSyms)
diff --git a/llvm/lib/MC/MCSectionCOFF.cpp b/llvm/lib/MC/MCSectionCOFF.cpp
index 94e29ce27d881..5bf14735eda9b 100644
--- a/llvm/lib/MC/MCSectionCOFF.cpp
+++ b/llvm/lib/MC/MCSectionCOFF.cpp
@@ -115,7 +115,3 @@ void MCSectionCOFF::printSwitchToSection(const MCAsmInfo &MAI, const Triple &T,
 }
 
 bool MCSectionCOFF::useCodeAlign() const { return isText(); }
-
-StringRef MCSectionCOFF::getVirtualSectionKind() const {
-  return "IMAGE_SCN_CNT_UNINITIALIZED_DATA";
-}
diff --git a/llvm/lib/MC/MCSectionELF.cpp b/llvm/lib/MC/MCSectionELF.cpp
index 299fe40706e3a..ef33f9c314579 100644
--- a/llvm/lib/MC/MCSectionELF.cpp
+++ b/llvm/lib/MC/MCSectionELF.cpp
@@ -215,5 +215,3 @@ void MCSectionELF::printSwitchToSection(const MCAsmInfo &MAI, const Triple &T,
 bool MCSectionELF::useCodeAlign() const {
   return getFlags() & ELF::SHF_EXECINSTR;
 }
-
-StringRef MCSectionELF::getVirtualSectionKind() const { return "SHT_NOBITS"; }
diff --git a/llvm/lib/MC/MCWin64EH.cpp b/llvm/lib/MC/MCWin64EH.cpp
index e8b26bf291ee4..a1c049aaed9cb 100644
--- a/llvm/lib/MC/MCWin64EH.cpp
+++ b/llvm/lib/MC/MCWin64EH.cpp
@@ -318,7 +318,7 @@ static void EmitUnwindInfo(MCStreamer &streamer, WinEH::FrameInfo *info) {
 
   // Emit the epilog instructions.
   if (EnableUnwindV2) {
-    MCFragment *DF = OS->getOrCreateDataFragment();
+    MCFragment *DF = OS->getCurrentFragment();
 
     bool IsLast = true;
     for (const auto &Epilog : llvm::reverse(info->EpilogMap)) {
diff --git a/llvm/lib/MC/MCWinCOFFStreamer.cpp b/llvm/lib/MC/MCWinCOFFStreamer.cpp
index 3398775df3f91..370280eb87cfd 100644
--- a/llvm/lib/MC/MCWinCOFFStreamer.cpp
+++ b/llvm/lib/MC/MCWinCOFFStreamer.cpp
@@ -278,7 +278,7 @@ void MCWinCOFFStreamer::emitCOFFSymbolIndex(MCSymbol const *Symbol) {
 
 void MCWinCOFFStreamer::emitCOFFSectionIndex(const MCSymbol *Symbol) {
   visitUsedSymbol(*Symbol);
-  MCFragment *DF = getOrCreateDataFragment();
+  MCFragment *DF = getCurrentFragment();
   const MCSymbolRefExpr *SRE = MCSymbolRefExpr::create(Symbol, getContext());
   MCFixup Fixup = MCFixup::create(DF->getContents().size(), SRE, FK_SecRel_2);
   DF->addFixup(Fixup);
@@ -288,7 +288,7 @@ void MCWinCOFFStreamer::emitCOFFSectionIndex(const MCSymbol *Symbol) {
 void MCWinCOFFStreamer::emitCOFFSecRel32(const MCSymbol *Symbol,
                                          uint64_t Offset) {
   visitUsedSymbol(*Symbol);
-  MCFragment *DF = getOrCreateDataFragment();
+  MCFragment *DF = getCurrentFragment();
   // Create Symbol A for the relocation relative reference.
   const MCExpr *MCE = MCSymbolRefExpr::create(Symbol, getContext());
   // Add the constant offset, if given.
@@ -306,7 +306,7 @@ void MCWinCOFFStreamer::emitCOFFSecRel32(const MCSymbol *Symbol,
 void MCWinCOFFStreamer::emitCOFFImgRel32(const MCSymbol *Symbol,
                                          int64_t Offset) {
   visitUsedSymbol(*Symbol);
-  MCFragment *DF = getOrCreateDataFragment();
+  MCFragment *DF = getCurrentFragment();
   // Create Symbol A for the relocation relative reference.
   const MCExpr *MCE = MCSymbolRefExpr::create(
       Symbol, MCSymbolRefExpr::VK_COFF_IMGREL32, getContext());
@@ -324,7 +324,7 @@ void MCWinCOFFStreamer::emitCOFFImgRel32(const MCSymbol *Symbol,
 
 void MCWinCOFFStreamer::emitCOFFSecNumber(MCSymbol const *Symbol) {
   visitUsedSymbol(*Symbol);
-  MCFragment *DF = getOrCreateDataFragment();
+  MCFragment *DF = getCurrentFragment();
   // Create Symbol for section number.
   const MCExpr *MCE = MCCOFFSectionNumberTargetExpr::create(
       *Symbol, this->getWriter(), getContext());
@@ -338,7 +338,7 @@ void MCWinCOFFStreamer::emitCOFFSecNumber(MCSymbol const *Symbol) {
 
 void MCWinCOFFStreamer::emitCOFFSecOffset(MCSymbol const *Symbol) {
   visitUsedSymbol(*Symbol);
-  MCFragment *DF = getOrCreateDataFragment();
+  MCFragment *DF = getCurrentFragment();
   // Create Symbol for section offset.
   const MCExpr *MCE =
       MCCOFFSectionOffsetTargetExpr::create(*Symbol, getContext());
diff --git a/llvm/lib/MC/MCXCOFFStreamer.cpp b/llvm/lib/MC/MCXCOFFStreamer.cpp
index 4d4529653aba9..63381b4f81859 100644
--- a/llvm/lib/MC/MCXCOFFStreamer.cpp
+++ b/llvm/lib/MC/MCXCOFFStreamer.cpp
@@ -89,7 +89,7 @@ void MCXCOFFStreamer::emitXCOFFSymbolLinkageWithVisibility(
 void MCXCOFFStreamer::emitXCOFFRefDirective(const MCSymbol *Symbol) {
   // Add a Fixup here to later record a relocation of type R_REF to prevent the
   // ref symbol from being garbage collected (by the binder).
-  MCFragment *DF = getOrCreateDataFragment();
+  MCFragment *DF = getCurrentFragment();
   const MCSymbolRefExpr *SRE = MCSymbolRefExpr::create(Symbol, getContext());
   std::optional<MCFixupKind> MaybeKind =
       getAssembler().getBackend().getFixupKind("R_REF");
diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMELFStreamer.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMELFStreamer.cpp
index eaba6fe5bfcb7..a7a9911de2d04 100644
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMELFStreamer.cpp
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMELFStreamer.cpp
@@ -593,7 +593,7 @@ class ARMELFStreamer : public MCELFStreamer {
         getContext().reportError(Loc, "relocated expression must be 32-bit");
         return;
       }
-      getOrCreateDataFragment();
+      getCurrentFragment();
     }
 
     emitDataMappingSymbol();
@@ -1207,7 +1207,7 @@ inline void ARMELFStreamer::SwitchToExIdxSection(const MCSymbol &FnStart) {
 }
 
 void ARMELFStreamer::EmitFixup(const MCExpr *Expr, MCFixupKind Kind) {
-  MCFragment *Frag = getOrCreateDataFragment();
+  MCFragment *Frag = getCurrentFragment();
   Frag->addFixup(MCFixup::create(Frag->getContents().size(), Expr, Kind));
 }
 
@@ -1295,7 +1295,7 @@ void ARMELFStreamer::EmitPersonalityFixup(StringRef Name) {
       MCSymbolRefExpr::create(PersonalitySym, ARM::S_ARM_NONE, getContext());
 
   visitUsedExpr(*PersonalityRef);
-  MCFragment *DF = getOrCreateDataFragment();
+  MCFragment *DF = getCurrentFragment();
   DF->addFixup(
       MCFixup::create(DF->getContents().size(), PersonalityRef, FK_Data_4));
 }
diff --git a/llvm/lib/Target/Mips/MCTargetDesc/MipsTargetStreamer.cpp b/llvm/lib/Target/Mips/MCTargetDesc/MipsTargetStreamer.cpp
index b89d6890903dd..5c7f34b870847 100644
--- a/llvm/lib/Target/Mips/MCTargetDesc/MipsTargetStreamer.cpp
+++ b/llvm/lib/Target/Mips/MCTargetDesc/MipsTargetStreamer.cpp
@@ -1033,42 +1033,42 @@ MCELFStreamer &MipsTargetELFStreamer::getStreamer() {
 }
 
 void MipsTargetELFStreamer::emitGPRel32Value(const MCExpr *Value) {
-  MCFragment *DF = getStreamer().getOrCreateDataFragment();
+  MCFragment *DF = getStreamer().getCurrentFragment();
   DF->addFixup(MCFixup::create(DF->getContents().size(), Value,
                                Mips::fixup_Mips_GPREL32));
   DF->appendContents(4, 0);
 }
 
 void MipsTargetELFStreamer::emitGPRel64Value(const MCExpr *Value) {
-  MCFragment *DF = getStreamer().getOrCreateDataFragment();
+  MCFragment *DF = getStreamer().getCurrentFragment();
   DF->addFixup(MCFixup::create(DF->getContents().size(), Value,
                                Mips::fixup_Mips_GPREL32));
   DF->appendContents(8, 0);
 }
 
 void MipsTargetELFStreamer::emitDTPRel32Value(const MCExpr *Value) {
-  MCFragment *DF = getStreamer().getOrCreateDataFragment();
+  MCFragment *DF = getStreamer().getCurrentFragment();
   DF->addFixup(MCFixup::create(DF->getContents().size(), Value,
                                Mips::fixup_Mips_DTPREL32));
   DF->appendContents(4, 0);
 }
 
 void MipsTargetELFStreamer::emitDTPRel64Value(const MCExpr *Value) {
-  MCFragment *DF = getStreamer().getOrCreateDataFragment();
+  MCFragment *DF = getStreamer().getCurrentFragment();
   DF->addFixup(MCFixup::create(DF->getContents().size(), Value,
                                Mips::fixup_Mips_DTPREL64));
   DF->appendContents(8, 0);
 }
 
 void MipsTargetELFStreamer::emitTPRel32Value(const MCExpr *Value) {
-  MCFragment *DF = getStreamer().getOrCreateDataFragment();
+  MCFragment *DF = getStreamer().getCurrentFragment();
   DF->addFixup(MCFixup::create(DF->getContents().size(), Value,
                                Mips::fixup_Mips_TPREL32));
   DF->appendContents(4, 0);
 }
 
 void MipsTargetELFStreamer::emitTPRel64Value(const MCExpr *Value) {
-  MCFragment *DF = getStreamer().getOrCreateDataFragment();
+  MCFragment *DF = getStreamer().getCurrentFragment();
   DF->addFixup(MCFixup::create(DF->getContents().size(), Value,
                                Mips::fixup_Mips_TPREL64));
   DF->appendContents(8, 0);
diff --git a/llvm/test/MC/COFF/bss-text.s b/llvm/test/MC/COFF/bss-text.s
index 439bd789dff2c..cedbb2f032236 100644
--- a/llvm/test/MC/COFF/bss-text.s
+++ b/llvm/test/MC/COFF/bss-text.s
@@ -4,11 +4,11 @@
 # RUN: llvm-mc -triple=x86_64-pc-win32 %s
 
 .bss
-# CHECK: <unknown>:0: error: IMAGE_SCN_CNT_UNINITIALIZED_DATA section '.bss' cannot have non-zero bytes
+# CHECK: <unknown>:0: error: BSS section '.bss' cannot have non-zero bytes
   addb %bl,(%rax)
 
 .section uninitialized,"b"
-# CHECK: <unknown>:0: error: IMAGE_SCN_CNT_UNINITIALIZED_DATA section 'uninitialized' cannot have non-zero bytes
+# CHECK: <unknown>:0: error: BSS section 'uninitialized' cannot have non-zero bytes
   jmp foo
 
 .section bss0,"b"
diff --git a/llvm/test/MC/ELF/nobits-non-zero-value.s b/llvm/test/MC/ELF/nobits-non-zero-value.s
index e9516aa3e835a..ea95ec97ac8d2 100644
--- a/llvm/test/MC/ELF/nobits-non-zero-value.s
+++ b/llvm/test/MC/ELF/nobits-non-zero-value.s
@@ -9,20 +9,37 @@
 .bss
   addb %al,(%rax)
 
-# CHECK: {{.*}}.s:[[#@LINE+1]]:11: warning: ignoring non-zero fill value in SHT_NOBITS section '.bss'
+# CHECK: {{.*}}.s:[[#@LINE+1]]:11: warning: ignoring non-zero fill value in BSS section '.bss'
 .align 4, 42
 
-.align 4, 0
-
   .long 1
 
 .section .bss0,"aw",%nobits
 addb %al,(%rax)
 
-.section .bss1,"aw",%nobits
+.section data_fixup,"aw",%nobits
 .quad foo
 
+.section fill,"aw",%nobits
+.fill b-a,1,1
+
+.section org,"aw",%nobits
+.org 1,1
+
+.section ok,"aw",%nobits
+.org 1
+.fill 1
+.fill b-a,1,0
+.align 4, 0
+.long 0
+
+.text
+a: nop
+b:
+
 ## Location is not tracked for efficiency.
-# CHECK: <unknown>:0: error: SHT_NOBITS section '.tbss' cannot have non-zero bytes
-# CHECK: <unknown>:0: error: SHT_NOBITS section '.bss' cannot have non-zero bytes
-# CHECK: <unknown>:0: error: SHT_NOBITS section '.bss1' cannot have fixups
+# CHECK: <unknown>:0: error: BSS section '.tbss' cannot have non-zero bytes
+# CHECK: <unknown>:0: error: BSS section '.bss' cannot have non-zero bytes
+# CHECK: <unknown>:0: error: BSS section 'data_fixup' cannot have fixups
+#...
[truncated]

... by eagerly allocating an empty fragment when adding a fragment with a variable-size tail. X86AsmBackend, The JCC erratum mitigation and x86-pad-for-align set a flag for FT_Relaxable, which needs to be moved to emitInstructionBegin. ``` if (CF->getKind() == MCFragment::FT_Relaxable) CF->setAllowAutoPadding(canPadInst(Inst, OS)); ``` Follow-up to #148544

Move the FT_Relaxable-in-BSS check from frequently-called MCObjectStreamer::emitInstruction to MCAssembler::writeSectionData, along with existing checks for other fragment types. For the uncommon diagnostics, losing the location information is acceptable.

MaskRay · 2025-07-20T16:51:02Z

I'll rename isVirtualSection IsVirtual separately. The a.out object file format has the BSS concept, which has been
inherited by COFF, XCOFF, Mach-O, ELF, and WebAssembly object file formats. LLVM should not create a term "virtual" that is confusing and not used elsewhere.

aengelke

LGTM

Add an assert to ensure `CurFrag` is either null or an `FT_Data` fragment. Follow-up to 39c8cfb. Extracted from #149721

Created using spr 1.3.5-bogner

* Handle non-zero fill values for `.fill` and `.org` directives. * Restore the fragment type check (5ee34ff removed a reachable `llvm_unreachable`) to detect unintended API usage. Remove virtual functions `getVirtualSectionKind` (added in https://reviews.llvm.org/D78138) as they are unnecessary in diagnostics. The a.out object file format has the BSS concept, which has been inherited by COFF, XCOFF, Mach-O, and ELF object file formats. Pull Request: llvm/llvm-project#149721

Add an assert to ensure `CurFrag` is either null or an `FT_Data` fragment. Follow-up to 39c8cfb. Extracted from llvm#149721

* Handle non-zero fill values for `.fill` and `.org` directives. * Restore the fragment type check (5ee34ff removed a reachable `llvm_unreachable`) to detect unintended API usage. Remove virtual functions `getVirtualSectionKind` (added in https://reviews.llvm.org/D78138) as they are unnecessary in diagnostics. The a.out object file format has the BSS concept, which has been inherited by COFF, XCOFF, Mach-O, and ELF object file formats. Pull Request: llvm#149721

Add an assert to ensure `CurFrag` is either null or an `FT_Data` fragment. Follow-up to 39c8cfb. Extracted from llvm#149721

* Handle non-zero fill values for `.fill` and `.org` directives. * Restore the fragment type check (5ee34ff removed a reachable `llvm_unreachable`) to detect unintended API usage. Remove virtual functions `getVirtualSectionKind` (added in https://reviews.llvm.org/D78138) as they are unnecessary in diagnostics. The a.out object file format has the BSS concept, which has been inherited by COFF, XCOFF, Mach-O, and ELF object file formats. Pull Request: llvm#149721

Add an assert to ensure `CurFrag` is either null or an `FT_Data` fragment. Follow-up to 39c8cfb. Extracted from llvm#149721

* Handle non-zero fill values for `.fill` and `.org` directives. * Restore the fragment type check (5ee34ff removed a reachable `llvm_unreachable`) to detect unintended API usage. Remove virtual functions `getVirtualSectionKind` (added in https://reviews.llvm.org/D78138) as they are unnecessary in diagnostics. The a.out object file format has the BSS concept, which has been inherited by COFF, XCOFF, Mach-O, and ELF object file formats. Pull Request: llvm#149721

[𝘀𝗽𝗿] initial version

1e95686

Created using spr 1.3.5-bogner

MaskRay requested a review from aengelke July 20, 2025 16:44

llvmbot added backend:ARM backend:MIPS llvm:mc Machine (object) code labels Jul 20, 2025

aengelke approved these changes Jul 20, 2025

View reviewed changes

MaskRay added a commit that referenced this pull request Jul 20, 2025

MC: Replace getOrCreateDataFragment with getCurrentFragment

ba6b705

Add an assert to ensure `CurFrag` is either null or an `FT_Data` fragment. Follow-up to 39c8cfb. Extracted from #149721

land the getCurrentFragment change separately and then rebase

2e6d029

Created using spr 1.3.5-bogner

MaskRay changed the title ~~MC: Clean up code related to fragments~~ MC: Fix fragment-in-BSS check Jul 20, 2025

MaskRay merged commit 673e542 into main Jul 20, 2025
7 of 9 checks passed

MaskRay deleted the users/MaskRay/spr/mc-clean-up-code-related-to-fragments branch July 20, 2025 18:11

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

MC: Fix fragment-in-BSS check #149721

MC: Fix fragment-in-BSS check #149721

Uh oh!

MaskRay commented Jul 20, 2025 •

edited

Loading

Uh oh!

llvmbot commented Jul 20, 2025 •

edited

Loading

Uh oh!

llvmbot commented Jul 20, 2025

Uh oh!

MaskRay commented Jul 20, 2025 •

edited

Loading

Uh oh!

aengelke left a comment

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants

MC: Fix fragment-in-BSS check #149721

MC: Fix fragment-in-BSS check #149721

Uh oh!

Conversation

MaskRay commented Jul 20, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

llvmbot commented Jul 20, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

llvmbot commented Jul 20, 2025

Uh oh!

MaskRay commented Jul 20, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

aengelke left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants

MaskRay commented Jul 20, 2025 •

edited

Loading

llvmbot commented Jul 20, 2025 •

edited

Loading

MaskRay commented Jul 20, 2025 •

edited

Loading