[lld] r246264 - Make sure we output symbols in the same order on 32 and 64 bit builds.

[Rafael Espindola via llvm-commits]

Author: rafael
Date: Thu Aug 27 21:46:41 2015
New Revision: 246264

URL: http://llvm.org/viewvc/llvm-project?rev=246264&view=rev
Log:
Make sure we output symbols in the same order on 32 and 64 bit builds.

Modified:
    lld/trunk/ELF/Writer.cpp
    lld/trunk/test/elf2/symbols.s

Modified: lld/trunk/ELF/Writer.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=246264&r1=246263&r2=246264&view=diff
==============================================================================
--- lld/trunk/ELF/Writer.cpp (original)
+++ lld/trunk/ELF/Writer.cpp Thu Aug 27 21:46:41 2015
@@ -16,6 +16,7 @@
 #include "Symbols.h"
 
 #include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/STLExtras.h"
 #include "llvm/Support/FileOutputBuffer.h"
 #include "llvm/Support/raw_ostream.h"
 
@@ -273,7 +274,18 @@ void StringTableSection<Is64Bits>::write
   memcpy(Buf, Data.data(), Data.size());
 }
 
+template <class ELFT>
+static int compareSym(const typename ELFFile<ELFT>::Elf_Sym *A,
+                      const typename ELFFile<ELFT>::Elf_Sym *B) {
+  uint32_t AN = A->st_name;
+  uint32_t BN = B->st_name;
+  assert(AN != BN);
+  return AN - BN;
+}
+
 template <class ELFT> void SymbolTableSection<ELFT>::writeTo(uint8_t *Buf) {
+  uint8_t *BufStart = Buf;
+
   Buf += sizeof(Elf_Sym);
   llvm::StringTableBuilder &Builder = Table.getStringBuilder();
   for (auto &P : Table.getSymbols()) {
@@ -326,6 +338,15 @@ template <class ELFT> void SymbolTableSe
 
     Buf += sizeof(Elf_Sym);
   }
+
+  // The order the global symbols are in is not defined. We can use an arbitrary
+  // order, but it has to be reproducible. That is true even when cross linking.
+  // The default hashing of StringRef produces different results on 32 and 64
+  // bit systems so we sort by st_name. That is arbitrary but deterministic.
+  // FIXME: Experiment with passing in a custom hashing instead.
+  auto *Syms = reinterpret_cast<Elf_Sym *>(BufStart);
+  ++Syms;
+  array_pod_sort(Syms, Syms + Table.getSymbols().size(), compareSym<ELFT>);
 }
 
 template <bool Is64Bits>

Modified: lld/trunk/test/elf2/symbols.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/elf2/symbols.s?rev=246264&r1=246263&r2=246264&view=diff
==============================================================================
--- lld/trunk/test/elf2/symbols.s (original)
+++ lld/trunk/test/elf2/symbols.s Thu Aug 27 21:46:41 2015
@@ -57,31 +57,22 @@ abs = 0x123
 // CHECK-NEXT:     Section: Undefined (0x0)
 // CHECK-NEXT:   }
 // CHECK-NEXT:   Symbol {
-// CHECK-NEXT:     Name: zed
-// CHECK-NEXT:     Value: 0x1004
+// CHECK-NEXT:     Name: _start
+// CHECK-NEXT:     Value: 0x1000
 // CHECK-NEXT:     Size: 0
 // CHECK-NEXT:     Binding: Global (0x1)
-// CHECK-NEXT:     Type: None
+// CHECK-NEXT:     Type: Function
 // CHECK-NEXT:     Other: 0
-// CHECK-NEXT:     Section: foobar
+// CHECK-NEXT:     Section: .text
 // CHECK-NEXT:   }
 // CHECK-NEXT:   Symbol {
-// CHECK-NEXT:     Name: zed3
-// CHECK-NEXT:     Value: 0x100C
-// CHECK-NEXT:     Size: 4
+// CHECK-NEXT:     Name: abs
+// CHECK-NEXT:     Value: 0x123
+// CHECK-NEXT:     Size: 0
 // CHECK-NEXT:     Binding: Global
 // CHECK-NEXT:     Type: None
 // CHECK-NEXT:     Other: 0
-// CHECK-NEXT:     Section: foobar
-// CHECK-NEXT:   }
-// CHECK-NEXT:   Symbol {
-// CHECK-NEXT:     Name: _start
-// CHECK-NEXT:     Value: 0x1000
-// CHECK-NEXT:     Size: 0
-// CHECK-NEXT:     Binding: Global (0x1)
-// CHECK-NEXT:     Type: Function
-// CHECK-NEXT:     Other: 0
-// CHECK-NEXT:     Section: .text
+// CHECK-NEXT:     Section: Absolute
 // CHECK-NEXT:   }
 // CHECK-NEXT:   Symbol {
 // CHECK-NEXT:     Name: bar
@@ -93,15 +84,6 @@ abs = 0x123
 // CHECK-NEXT:     Section: Undefined (0x0)
 // CHECK-NEXT:   }
 // CHECK-NEXT:   Symbol {
-// CHECK-NEXT:     Name: abs
-// CHECK-NEXT:     Value: 0x123
-// CHECK-NEXT:     Size: 0
-// CHECK-NEXT:     Binding: Global
-// CHECK-NEXT:     Type: None
-// CHECK-NEXT:     Other: 0
-// CHECK-NEXT:     Section: Absolute
-// CHECK-NEXT:   }
-// CHECK-NEXT:   Symbol {
 // CHECK-NEXT:     Name: foo
 // CHECK-NEXT:     Value: 0x1000
 // CHECK-NEXT:     Size: 0
@@ -111,6 +93,24 @@ abs = 0x123
 // CHECK-NEXT:     Section: .text
 // CHECK-NEXT:   }
 // CHECK-NEXT:   Symbol {
+// CHECK-NEXT:     Name: zed
+// CHECK-NEXT:     Value: 0x1004
+// CHECK-NEXT:     Size: 0
+// CHECK-NEXT:     Binding: Global (0x1)
+// CHECK-NEXT:     Type: None
+// CHECK-NEXT:     Other: 0
+// CHECK-NEXT:     Section: foobar
+// CHECK-NEXT:   }
+// CHECK-NEXT:   Symbol {
+// CHECK-NEXT:     Name: zed3
+// CHECK-NEXT:     Value: 0x100C
+// CHECK-NEXT:     Size: 4
+// CHECK-NEXT:     Binding: Global
+// CHECK-NEXT:     Type: None
+// CHECK-NEXT:     Other: 0
+// CHECK-NEXT:     Section: foobar
+// CHECK-NEXT:   }
+// CHECK-NEXT:   Symbol {
 // CHECK-NEXT:     Name: zed2
 // CHECK-NEXT:     Value: 0x1008
 // CHECK-NEXT:     Size: 0