From 871765c3214fbc03cbbab339a74974b282512be7 Mon Sep 17 00:00:00 2001
From: Rafael Espindola <rafael.espindola@gmail.com>
Date: Fri, 28 Aug 2015 02:46:41 +0000
Subject: [PATCH] Make sure we output symbols in the same order on 32 and 64
 bit builds.

llvm-svn: 246264
---
 lld/ELF/Writer.cpp      | 21 ++++++++++++
 lld/test/elf2/symbols.s | 72 ++++++++++++++++++++---------------------
 2 files changed, 57 insertions(+), 36 deletions(-)

diff --git a/lld/ELF/Writer.cpp b/lld/ELF/Writer.cpp
index c42b0e647c48..244d4fd462d0 100644
--- a/lld/ELF/Writer.cpp
+++ b/lld/ELF/Writer.cpp
@@ -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>::writeTo(uint8_t *Buf) {
   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 SymbolTableSection<ELFT>::writeTo(uint8_t *Buf) {
 
     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>
diff --git a/lld/test/elf2/symbols.s b/lld/test/elf2/symbols.s
index 44a478757e80..5d1ef3a630e2 100644
--- a/lld/test/elf2/symbols.s
+++ b/lld/test/elf2/symbols.s
@@ -57,6 +57,42 @@ abs = 0x123
 // CHECK-NEXT:     Section: Undefined (0x0)
 // 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:   }
+// 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: bar
+// CHECK-NEXT:     Value: 0x0
+// CHECK-NEXT:     Size: 0
+// CHECK-NEXT:     Binding: Weak (0x2)
+// CHECK-NEXT:     Type: Object (0x1)
+// CHECK-NEXT:     Other: 0
+// CHECK-NEXT:     Section: Undefined (0x0)
+// CHECK-NEXT:   }
+// CHECK-NEXT:   Symbol {
+// CHECK-NEXT:     Name: foo
+// CHECK-NEXT:     Value: 0x1000
+// CHECK-NEXT:     Size: 0
+// CHECK-NEXT:     Binding: Weak (0x2)
+// CHECK-NEXT:     Type: Object
+// CHECK-NEXT:     Other: 0
+// CHECK-NEXT:     Section: .text
+// CHECK-NEXT:   }
+// CHECK-NEXT:   Symbol {
 // CHECK-NEXT:     Name: zed
 // CHECK-NEXT:     Value: 0x1004
 // CHECK-NEXT:     Size: 0
@@ -75,42 +111,6 @@ abs = 0x123
 // 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:   }
-// CHECK-NEXT:   Symbol {
-// CHECK-NEXT:     Name: bar
-// CHECK-NEXT:     Value: 0x0
-// CHECK-NEXT:     Size: 0
-// CHECK-NEXT:     Binding: Weak (0x2)
-// CHECK-NEXT:     Type: Object (0x1)
-// CHECK-NEXT:     Other: 0
-// 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
-// CHECK-NEXT:     Binding: Weak (0x2)
-// CHECK-NEXT:     Type: Object
-// CHECK-NEXT:     Other: 0
-// CHECK-NEXT:     Section: .text
-// CHECK-NEXT:   }
-// CHECK-NEXT:   Symbol {
 // CHECK-NEXT:     Name: zed2
 // CHECK-NEXT:     Value: 0x1008
 // CHECK-NEXT:     Size: 0