Disallow redefinition of section symbols.

[eugenis]

Summary

Fixes PR31850.

[eugenis]

friendly ping

lib/MC/MCContext.cpp

 MCSectionELF *MCContext::createELFSectionImpl(StringRef Section, unsigned Type,
                                               unsigned Flags, SectionKind K,
                                               unsigned EntrySize,
                                               const MCSymbolELF *Group,
                                               unsigned UniqueID,
                                               const MCSectionELF *Associated) {
   MCSymbolELF *R;
   MCSymbol *&Sym = Symbols[Section];
+  // A section symbol can not redefine regular symbols. There may be multiple
+  // sections with the same name, in which case the first such section wins.
+  if (Sym && Sym->isDefined() &&
+      (!Sym->isInSection() || Sym->getSection().getBeginSymbol() != Sym))
+    reportError(SMLoc(), "invalid symbol redefinition");
   if (Sym && Sym->isUndefined()) {
     R = cast<MCSymbolELF>(Sym);
   } else {
     auto NameIter = UsedNames.insert(std::make_pair(Section, false)).first;
     R = new (&*NameIter, *this) MCSymbolELF(&*NameIter, /*isTemporary*/ false);
     if (!Sym)
       Sym = R;
   }
   R->setBinding(ELF::STB_LOCAL);
   R->setType(ELF::STT_SECTION);
-  R->setRedefinable(true);
 
   auto *Ret = new (ELFAllocator.Allocate()) MCSectionELF(
       Section, Type, Flags, K, EntrySize, Group, UniqueID, R, Associated);
 
   auto *F = new MCDataFragment();
   Ret->getFragmentList().insert(Ret->begin(), F);
   F->setParent(Ret);
   R->setFragment(F);

test/CodeGen/XCore/section-name.ll

-; RUN: llc < %s -march=xcore
+; RUN: not llc < %s -march=xcore 2>&1 | FileCheck %s
 
-; we used to crash in this.
 @bar = internal global i32 zeroinitializer
 
 define void @".dp.bss"() {
   ret void
 }
+
+; CHECK: LLVM ERROR: invalid symbol redefinition

test/MC/ELF/section-sym-err.s

+// RUN: not llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o %t.o 2>&1 | FileCheck %s
+
+.section foo
+foo:
+
+// CHECK: error: invalid symbol redefinition

test/MC/ELF/section-sym-err2.s

+// RUN: not llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o %t.o 2>&1 | FileCheck %s
+
+foo:
+.section foo
+
+// CHECK: error: invalid symbol redefinition

test/MC/ELF/section-sym-redefine.s

-// RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o - | llvm-readobj  -t -r --expand-relocs | FileCheck %s
-
-// Local symbol overriding section.
-.section x1,"a",@progbits
-.local  x1
-.comm   x1,4,4
-.long x1  // reloc: .bss + 0
-
-// Section declared after local. Local symbol wins.
-.local  x2
-.comm   x2,4,4
-.section x2,"a",@progbits
-.long x2  // reloc: .bss + 4
-
-// No overriding symbol.
-.section x3,"a",@progbits
-.long x3  // reloc: x3(section) + 0
-
-// Global vs section.
-.section x4,"a",@progbits
-.long 0
-.globl x4
-.section foo, "a", @progbits
-x4:
-.long 0
-.long x4  // reloc: x4(global) + 0
-
-// Global vs implicit section
-.globl .data
-.data:
-.long 42
-.long .data // reloc: .data(global) + 0
-
-// CHECK: Relocations [
-// CHECK:   Section (4) .relax1 {
-// CHECK:     Relocation {
-// CHECK:       Offset: 0x0
-// CHECK:       Type: R_X86_64_32 (10)
-// CHECK:       Symbol: .bss (3)
-// CHECK:       Addend: 0x0
-// CHECK:     }
-// CHECK:   }
-// CHECK:   Section (7) .relax2 {
-// CHECK:     Relocation {
-// CHECK:       Offset: 0x0
-// CHECK:       Type: R_X86_64_32 (10)
-// CHECK:       Symbol: .bss (3)
-// CHECK:       Addend: 0x4
-// CHECK:     }
-// CHECK:   }
-// CHECK:   Section (9) .relax3 {
-// CHECK:     Relocation {
-// CHECK:       Offset: 0x0
-// CHECK:       Type: R_X86_64_32 (10)
-// CHECK:       Symbol: x3 (4)
-// CHECK:       Addend: 0x0
-// CHECK:     }
-// CHECK:   }
-// CHECK:   Section (12) .relafoo {
-// CHECK:     Relocation {
-// CHECK:       Offset: 0x4
-// CHECK:       Type: R_X86_64_32 (10)
-// CHECK:       Symbol: x4 (6)
-// CHECK:       Addend: 0x0
-// CHECK:     }
-// CHECK:     Relocation {
-// CHECK:       Offset: 0xC
-// CHECK:       Type: R_X86_64_32 (10)
-// CHECK:       Symbol: .data (5)
-// CHECK:       Addend: 0x0
-// CHECK:     }
-// CHECK:   }
-// CHECK: ]
-// CHECK: Symbols [
-// CHECK:   Symbol {
-// CHECK:     Name:  (0)
-// CHECK:     Value: 0x0
-// CHECK:     Size: 0
-// CHECK:     Binding: Local (0x0)
-// CHECK:     Type: None (0x0)
-// CHECK:     Other: 0
-// CHECK:     Section: Undefined (0x0)
-// CHECK:   }
-// CHECK:   Symbol {
-// CHECK:     Name: x1 (67)
-// CHECK:     Value: 0x0
-// CHECK:     Size: 4
-// CHECK:     Binding: Local (0x0)
-// CHECK:     Type: Object (0x1)
-// CHECK:     Other: 0
-// CHECK:     Section: .bss (0x5)
-// CHECK:   }
-// CHECK:   Symbol {
-// CHECK:     Name: x2 (59)
-// CHECK:     Value: 0x4
-// CHECK:     Size: 4
-// CHECK:     Binding: Local (0x0)
-// CHECK:     Type: Object (0x1)
-// CHECK:     Other: 0
-// CHECK:     Section: .bss (0x5)
-// CHECK:   }
-// CHECK:   Symbol {
-// CHECK:     Name:  (0)
-// CHECK:     Value: 0x0
-// CHECK:     Size: 0
-// CHECK:     Binding: Local (0x0)
-// CHECK:     Type: Section (0x3)
-// CHECK:     Other: 0
-// CHECK:     Section: .bss (0x5)
-// CHECK:   }
-// CHECK:   Symbol {
-// CHECK:     Name:  (0)
-// CHECK:     Value: 0x0
-// CHECK:     Size: 0
-// CHECK:     Binding: Local (0x0)
-// CHECK:     Type: Section (0x3)
-// CHECK:     Other: 0
-// CHECK:     Section: x3 (0x8)
-// CHECK:   }
-// CHECK:   Symbol {
-// CHECK:     Name: .data (37)
-// CHECK:     Value: 0x8
-// CHECK:     Size: 0
-// CHECK:     Binding: Global (0x1)
-// CHECK:     Type: None (0x0)
-// CHECK:     Other: 0
-// CHECK:     Section: foo (0xB)
-// CHECK:   }
-// CHECK:   Symbol {
-// CHECK:     Name: x4 (43)
-// CHECK:     Value: 0x0
-// CHECK:     Size: 0
-// CHECK:     Binding: Global (0x1)
-// CHECK:     Type: None (0x0)
-// CHECK:     Other: 0
-// CHECK:     Section: foo (0xB)
-// CHECK:   }
-// CHECK: ]

test/MC/ELF/section.s

 // CHECK-NEXT:   Link: 0
 // CHECK-NEXT:   Info: 0
 // CHECK-NEXT:   AddressAlignment: 1
 // CHECK-NEXT:   EntrySize: 0
 // CHECK-NEXT: }
 
 // Test that we handle the strings like gas
 .section bar-"foo"
-.section "foo"
+.section "fooo"
+
 
 // CHECK:        Section {
 // CHECK:          Name: bar-"foo"
 // CHECK:        Section {
-// CHECK:          Name: foo
+// CHECK:          Name: fooo
 
 // Test SHF_LINK_ORDER
 
 .section .shf_metadata_target1, "a"
         .quad 0
 .section .shf_metadata_target2, "a", @progbits, unique, 1
 .Lshf_metadata_target2_1:
         .quad 0