[PATCH] D59496: [llvm-objcopy] - Fix a st_name of the first symbol table entry.

[George Rimar via Phabricator via llvm-commits]

grimar updated this revision to Diff 191496.
grimar marked an inline comment as done.
grimar added a comment.

- Updated implementation.

So `StringTableBuilder` reserves a null byte at start for ELF tables:
https://github.com/llvm-mirror/llvm/blob/master/lib/MC/StringTableBuilder.cpp#L38

Seems what we want is just to use it explicitly. For that, I reassign the index of an empty string after finalization.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D59496/new/

https://reviews.llvm.org/D59496

Files:
  lib/MC/StringTableBuilder.cpp
  test/tools/llvm-objcopy/ELF/symbol-empty-name.test


Index: test/tools/llvm-objcopy/ELF/symbol-empty-name.test
===================================================================
--- /dev/null
+++ test/tools/llvm-objcopy/ELF/symbol-empty-name.test
@@ -0,0 +1,47 @@
+# RUN: yaml2obj %s > %t
+# RUN: llvm-objcopy %t %t2
+# RUN: llvm-readobj -t %t2 | FileCheck %s
+
+## Check that all values of the null symbol are zeroes.
+
+# CHECK:      Symbols [
+# CHECK-NEXT:  Symbol {
+# CHECK-NEXT:    Name:  (0)
+# 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: Undefined (0x0)
+# CHECK-NEXT:  }
+
+## Check we emit a zero in st_name field when a symbol has no name.
+
+# CHECK:       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 (0x1)
+# CHECK-NEXT: }
+
+!ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_EXEC
+  Machine: EM_X86_64
+Sections:
+  - Name:  .text
+    Type:  SHT_PROGBITS
+    Flags: [ SHF_ALLOC, SHF_EXECINSTR ]
+Symbols:
+  Local:
+    - Name:    ""
+      Type:    STT_SECTION
+      Section: .text
+  Global:
+  # We need to have a named symbol, otherwise the original
+  # issue that was fixed is not reproduced by this test.
+    - Name: foo
Index: lib/MC/StringTableBuilder.cpp
===================================================================
--- lib/MC/StringTableBuilder.cpp
+++ lib/MC/StringTableBuilder.cpp
@@ -159,6 +159,11 @@
 
   if (K == MachO)
     Size = alignTo(Size, 4); // Pad to multiple of 4.
+
+  // Empty strings in according to ELF specification should have zero indexes.
+  // In initSize() we explicitly reserved a null byte at the start for that.
+  if (K == ELF)
+    StringIndexMap[CachedHashStringRef("")] = 0;
 }
 
 void StringTableBuilder::clear() {


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