[llvm-readobj] Display section names for STT_SECTION symbols.

[mattd]

Summary

This patch will obtain the section name for symbols that refer to a section. Prior to this patch the Name field for STT_SECTIONs was blank, now it is populated.

Before:

Symbol table '.symtab' contains 6 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
     0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT  UND
     1: 0000000000000000     0 SECTION LOCAL  DEFAULT    1
     2: 0000000000000000     0 SECTION LOCAL  DEFAULT    3
     3: 0000000000000000     0 SECTION LOCAL  DEFAULT    4
     4: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT  UND _GLOBAL_OFFSET_TABLE_
     5: 0000000000000000     0 TLS     GLOBAL DEFAULT  UND sym

With this patch:

Symbol table '.symtab' contains 6 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
     0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT  UND
     1: 0000000000000000     0 SECTION LOCAL  DEFAULT    1 .text
     2: 0000000000000000     0 SECTION LOCAL  DEFAULT    3 .data
     3: 0000000000000000     0 SECTION LOCAL  DEFAULT    4 .bss
     4: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT  UND _GLOBAL_OFFSET_TABLE_
     5: 0000000000000000     0 TLS     GLOBAL DEFAULT  UND sym

This fixes PR40788

[MaskRay]

llvm/tools/llvm-readobj/ELFDumper.cpp

818

SymbolName.empty()

[MaskRay]

llvm/tools/llvm-readobj/ELFDumper.cpp

821

auto -> Elf_Sym_Range

[jhenderson]

The request changes is due to the test. Otherwise this basically looks fine to me.

llvm/test/tools/llvm-readobj/symbols.test

17–19

There is already a separate test for this that needs updating instead. See gnu-symbols.test.

llvm/tools/llvm-readobj/ELFDumper.cpp

823

I don't think you need this if at all. If the section name is empty and the symbol name is empty, I think we should just print an empty string (section symbols aren't versioned to my knowledge).

[mattd]

Thanks for the reviews everyone. This update addresses the feedback, all of which was incorporated.

[jhenderson]

LGTM.

llvm/test/MC/ARM/arm-elf-symver.s

 @ CHECK-NEXT:     Value: 0x0
 @ CHECK-NEXT:     Size: 0
 @ CHECK-NEXT:     Binding: Local (0x0)
 @ CHECK-NEXT:     Type: None (0x0)
 @ CHECK-NEXT:     Other: 0
 @ CHECK-NEXT:     Section: .text
 @ CHECK-NEXT:   }
 @ CHECK-NEXT:   Symbol {
-@ CHECK-NEXT:     Name: (0)
+@ CHECK-NEXT:     Name: .text (0)
 @ CHECK-NEXT:     Value: 0x0
 @ CHECK-NEXT:     Size: 0
 @ CHECK-NEXT:     Binding: Local (0x0)
 @ CHECK-NEXT:     Type: Section (0x3)
 @ CHECK-NEXT:     Other: 0
 @ CHECK-NEXT:     Section: .text
 @ CHECK-NEXT:   }
 @ CHECK-NEXT:   Symbol {

llvm/test/MC/ELF/alias.s

 // CHECK-NEXT:     Value: 0x1
 // CHECK-NEXT:     Size: 0
 // CHECK-NEXT:     Binding: Local
 // CHECK-NEXT:     Type: Function
 // CHECK-NEXT:     Other: 0
 // CHECK-NEXT:     Section: .text
 // CHECK-NEXT:   }
 // CHECK-NEXT:   Symbol {
-// CHECK-NEXT:     Name: (0)
+// CHECK-NEXT:     Name: .data (0)
 // CHECK-NOT: Symbol {
 // CHECK:        }
 // CHECK-NEXT:   Symbol {
 // CHECK-NEXT:     Name: bar2
 // CHECK-NEXT:     Value: 0x0
 // CHECK-NEXT:     Size: 0
 // CHECK-NEXT:     Binding: Global
 // CHECK-NEXT:     Type: None

llvm/test/MC/ELF/many-sections-2.s

 // SYMBOLS-NEXT:    Binding: Local (0x0)
 // SYMBOLS-NEXT:    Type: None (0x0)
 // SYMBOLS-NEXT:    Other: 0
 // SYMBOLS-NEXT:    Section: dm (0xFF00)
 // SYMBOLS-NEXT:  }
 
 
 // Test that this file has one section too many.
-// SYMBOLS:         Name: (0)
+// SYMBOLS:         Name: dm (0)
 // SYMBOLS:         Value: 0x0
 // SYMBOLS:         Size: 0
 // SYMBOLS:         Binding: Local (0x0)
 // SYMBOLS:         Type: Section (0x3)
 // SYMBOLS:         Other: 0
 // SYMBOLS:         Section: dm (0xFF00)
 // SYMBOLS-NEXT:  }
 // SYMBOLS-NEXT:]

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

 // CHECK-NEXT:    Value: 0x0
 // CHECK-NEXT:    Size: 0
 // CHECK-NEXT:    Binding: Local (0x0)
 // CHECK-NEXT:    Type: None (0x0)
 // CHECK-NEXT:    Other: 0
 // CHECK-NEXT:    Section: .group
 // CHECK-NEXT:  }
 // CHECK-NEXT:  Symbol {
-// CHECK-NEXT:    Name:  (0)
+// CHECK-NEXT:    Name:  foo (0)
 // CHECK-NEXT:    Value: 0x0
 // CHECK-NEXT:    Size: 0
 // CHECK-NEXT:    Binding: Local (0x0)
 // CHECK-NEXT:    Type: Section (0x3)
 // CHECK-NEXT:    Other: 0
 // CHECK-NEXT:    Section: foo (0x4)
 // CHECK-NEXT:  }
 // CHECK-NEXT: ]

llvm/test/MC/ELF/symver.s

 // CHECK-NEXT:     Value: 0x0
 // CHECK-NEXT:     Size: 0
 // CHECK-NEXT:     Binding: Local
 // CHECK-NEXT:     Type: None
 // CHECK-NEXT:     Other: 0
 // CHECK-NEXT:     Section: .text
 // CHECK-NEXT:   }
 // CHECK-NEXT:   Symbol {
-// CHECK-NEXT:     Name: (0)
+// CHECK-NEXT:     Name: .text (0)
 // CHECK-NEXT:     Value: 0x0
 // CHECK-NEXT:     Size: 0
 // CHECK-NEXT:     Binding: Local
 // CHECK-NEXT:     Type: Section
 // CHECK-NEXT:     Other: 0
 // CHECK-NEXT:     Section: .text
 // CHECK-NEXT:   }
 // CHECK-NEXT:   Symbol {

llvm/test/MC/ELF/weakref.s

 // CHECK-NEXT:     Value: 0x20
 // CHECK-NEXT:     Size: 0
 // CHECK-NEXT:     Binding: Local
 // CHECK-NEXT:     Type: None
 // CHECK-NEXT:     Other: 0
 // CHECK-NEXT:     Section: .text
 // CHECK-NEXT:   }
 // CHECK-NEXT:   Symbol {
-// CHECK-NEXT:     Name: (0)
+// CHECK-NEXT:     Name: .text (0)
 // CHECK-NEXT:     Value: 0x0
 // CHECK-NEXT:     Size: 0
 // CHECK-NEXT:     Binding: Local
 // CHECK-NEXT:     Type: Section
 // CHECK-NEXT:     Other: 0
 // CHECK-NEXT:     Section: .text
 // CHECK-NEXT:   }
 // CHECK-NEXT:   Symbol {

llvm/test/Object/readobj-shared-object.test

 ELF:     Type: SHT_STRTAB
 ELF:     Flags [ (0x0)
 ELF:     ]
 ELF:   }
 ELF: ]
 
 ELF: Symbols [
 ELF:   Symbol {
-ELF:     Name: (0)
+ELF:     Name: .hash (0)
 ELF:     Binding: Local
 ELF:     Type: Section
 ELF:     Section: .hash
 ELF:   }
 ELF:   Symbol {
-ELF:     Name: (0)
+ELF:     Name: .dynsym (0)
 ELF:     Binding: Local
 ELF:     Type: Section
 ELF:     Section: .dynsym
 ELF:   }
 ELF:   Symbol {
-ELF:     Name: (0)
+ELF:     Name: .dynstr (0)
 ELF:     Binding: Local
 ELF:     Type: Section
 ELF:     Section: .dynstr
 ELF:   }
 ELF:   Symbol {
-ELF:     Name: (0)
+ELF:     Name: .text (0)
 ELF:     Binding: Local
 ELF:     Type: Section
 ELF:     Section: .text
 ELF:   }
 ELF:   Symbol {
-ELF:     Name: (0)
+ELF:     Name: .eh_frame (0)
 ELF:     Binding: Local
 ELF:     Type: Section
 ELF:     Section: .eh_frame
 ELF:   }
 ELF:   Symbol {
-ELF:     Name: (0)
+ELF:     Name: .tdata (0)
 ELF:     Binding: Local
 ELF:     Type: Section
 ELF:     Section: .tdata
 ELF:   }
 ELF:   Symbol {
-ELF:     Name: (0)
+ELF:     Name: .dynamic (0)
 ELF:     Binding: Local
 ELF:     Type: Section
 ELF:     Section: .dynamic
 ELF:   }
 ELF:   Symbol {
-ELF:     Name: (0)
+ELF:     Name: .got.plt (0)
 ELF:     Binding: Local
 ELF:     Type: Section
 ELF:     Section: .got.plt
 ELF:   }
 ELF:   Symbol {
-ELF:     Name: (0)
+ELF:     Name: .data (0)
 ELF:     Binding: Local
 ELF:     Type: Section
 ELF:     Section: .data
 ELF:   }
 ELF:   Symbol {
-ELF:     Name: (0)
+ELF:     Name: .bss (0)
 ELF:     Binding: Local
 ELF:     Type: Section
 ELF:     Section: .bss
 ELF:   }
 ELF:   Symbol {
 ELF:     Name: shared.ll
 ELF:     Binding: Local
 ELF:     Type: File

llvm/test/tools/llvm-readobj/sections-ext.test

 ELF-NEXT:     Link: 0
 ELF-NEXT:     Info: 0
 ELF-NEXT:     AddressAlignment: 16
 ELF-NEXT:     EntrySize: 0
 ELF-NEXT:     Relocations [
 ELF-NEXT:     ]
 ELF-NEXT:     Symbols [
 ELF-NEXT:       Symbol {
-ELF-NEXT:         Name: (0)
+ELF-NEXT:         Name: .text (0)
 ELF-NEXT:         Value: 0x0
 ELF-NEXT:         Size: 0
 ELF-NEXT:         Binding: Local (0x0)
 ELF-NEXT:         Type: Section (0x3)
 ELF-NEXT:         Other: 0
 ELF-NEXT:         Section: .text (0x1)
 ELF-NEXT:       }
 ELF-NEXT:       Symbol {

llvm/test/tools/llvm-readobj/symbols.test

 RUN: llvm-readobj --symbols %p/Inputs/trivial.obj.coff-i386 \
 RUN:   | FileCheck %s -check-prefix COFF
 RUN: llvm-readobj --symbols %p/Inputs/trivial.obj.elf-i386 \
 RUN:   | FileCheck %s -check-prefix ELF
 RUN: llvm-readobj --symbols %p/Inputs/trivial.obj.wasm \
 RUN:   | FileCheck %s -check-prefix WASM
 
 # Check flag aliases produce identical output.
 RUN: llvm-readobj --symbols %p/Inputs/trivial.obj.elf-i386 > %t.symbols
 RUN: llvm-readobj --syms %p/Inputs/trivial.obj.elf-i386 > %t.syms
 RUN: cmp %t.symbols %t.syms
 RUN: llvm-readobj -t %p/Inputs/trivial.obj.elf-i386 > %t.t
 RUN: cmp %t.symbols %t.t
 RUN: llvm-readelf -s -elf-output-style LLVM %p/Inputs/trivial.obj.elf-i386 > %t.lowers
 RUN: cmp %t.symbols %t.lowers
 
+# Check the GNU presentation of the output.
+RUN: llvm-readelf --symbols %p/Inputs/trivial.obj.elf-i386 \
+RUN:   | FileCheck %s -check-prefix ELF-GNU
+
 COFF:      Symbols [
 COFF-NEXT:   Symbol {
 COFF-NEXT:     Name: @comp.id
 COFF-NEXT:    Value: 14766605
 COFF-NEXT:    Section:  IMAGE_SYM_ABSOLUTE (-1)
 COFF-NEXT:     BaseType: Null (0x0)
 COFF-NEXT:     ComplexType: Null (0x0)
 COFF-NEXT:    StorageClass: Static (0x3)

 WASM-NEXT:     Flags [ (0x10)
 WASM-NEXT:       UNDEFINED (0x10)
 WASM-NEXT:     ]
 WASM-NEXT:     ImportName: SomeOtherFunction
 WASM-NEXT:     ImportModule: env
 WASM-NEXT:     ElementIndex: 0x1
 WASM-NEXT:   }
 WASM-NEXT: ]
+
+ELF-GNU:      Symbol table '.symtab' contains 12 entries:
+ELF-GNU-NEXT:    Num:    Value  Size Type    Bind   Vis      Ndx Name
+ELF-GNU-NEXT:      0: 00000000     0 NOTYPE  LOCAL  DEFAULT  UND 
+ELF-GNU-NEXT:      1: 00000000     0 FILE    LOCAL  DEFAULT  ABS trivial.ll
+ELF-GNU-NEXT:      2: 00000000    13 OBJECT  LOCAL  DEFAULT    5 .L.str
+ELF-GNU-NEXT:      3: 00000000     0 SECTION LOCAL  DEFAULT    1 .text
+ELF-GNU-NEXT:      4: 00000000     0 SECTION LOCAL  DEFAULT    3 .data
+ELF-GNU-NEXT:      5: 00000000     0 SECTION LOCAL  DEFAULT    4 .bss
+ELF-GNU-NEXT:      6: 00000000     0 SECTION LOCAL  DEFAULT    5 .rodata.str1.1
+ELF-GNU-NEXT:      7: 00000000     0 SECTION LOCAL  DEFAULT    6 .note.GNU-stack
+ELF-GNU-NEXT:      8: 00000000    42 FUNC    GLOBAL DEFAULT    1 main
+ELF-GNU-NEXT:      9: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND SomeOtherFunction
+ELF-GNU-NEXT:     10: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND _GLOBAL_OFFSET_TABLE_
+ELF-GNU-NEXT:     11: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND puts

llvm/tools/llvm-readobj/ELFDumper.cpp

 }
 
 template <typename ELFT>
 std::string ELFDumper<ELFT>::getFullSymbolName(const Elf_Sym *Symbol,
                                                StringRef StrTable,
                                                bool IsDynamic) const {
   std::string SymbolName =
       maybeDemangle(unwrapOrError(Symbol->getName(StrTable)));
+
+  if (SymbolName.size() == 0 && Symbol->getType() == ELF::STT_SECTION) {
+    unsigned SectionIndex;
+    StringRef SectionName;
+    auto Syms = unwrapOrError(ObjF->getELFFile()->symbols(DotSymtabSec));
+    getSectionNameIndex(Symbol, Syms.begin(), SectionName, SectionIndex);
+    if (SectionName.size())
+      return SectionName;
+  }
+
   if (!IsDynamic)
     return SymbolName;
 
   bool IsDefault;
   StringRef Version = getSymbolVersion(StrTable, &*Symbol, IsDefault);
   if (!Version.empty()) {
     SymbolName += (IsDefault ? "@@" : "@");
     SymbolName += Version;