Revert "Reland D64327 [MC][ELF] Allow STT_SECTION referencing SHF_MERGE on REL targets"

This reverts commit b497665d98ad5026b1d3d67d5793a28fefe27bea.

Spent some time trying to reproduce this locally, reverting in a
desparate attempt to fix the sanitizer buildbot:
 - http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux/builds/28828

I don't know exactly why or how this patch breaks the bots, but it seems
pretty concrete that it's the culprit.

cmake/modules/AddLLVM.cmake

@@ -222,13 +222,8 @@ function(add_link_opts target_name)
     # Pass -O3 to the linker. This enabled different optimizations on different
     # linkers.
     if(NOT (${CMAKE_SYSTEM_NAME} MATCHES "Darwin|SunOS|AIX" OR WIN32))
-      # Before binutils 2.34, gold -O2 and above did not correctly handle R_386_GOTOFF to
-      # SHF_MERGE|SHF_STRINGS sections: https://sourceware.org/bugzilla/show_bug.cgi?id=16794
-      if(LLVM_LINKER_IS_GOLD)
-        set_property(TARGET ${target_name} APPEND_STRING PROPERTY LINK_FLAGS " -Wl,-O1")
-      else()
-        set_property(TARGET ${target_name} APPEND_STRING PROPERTY LINK_FLAGS " -Wl,-O3")
-      endif()
+      set_property(TARGET ${target_name} APPEND_STRING PROPERTY
+                   LINK_FLAGS " -Wl,-O3")
     endif()
 
     if(LLVM_LINKER_IS_GOLD)

lib/MC/ELFObjectWriter.cpp

@@ -1393,6 +1393,11 @@ bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
     if (Flags & ELF::SHF_MERGE) {
       if (C != 0)
         return true;
+
+      // It looks like gold has a bug (http://sourceware.org/PR16794) and can
+      // only handle section relocations to mergeable sections if using RELA.
+      if (!hasRelocationAddend())
+        return true;
     }
 
     // Most TLS relocations use a got, so they need the symbol. Even those that

test/MC/ELF/basic-elf-32.s

@@ -46,9 +46,9 @@ main:                                   # @main
 
 // CHECK: Relocations [
 // CHECK:   Section {{.*}} .rel.text {
-// CHECK:     0x6  R_386_32   .rodata.str1.1 0x0
+// CHECK:     0x6  R_386_32   .L.str1
 // CHECK:     0xB  R_386_PC32 puts
-// CHECK:     0x12 R_386_32   .rodata.str1.1 0x0
+// CHECK:     0x12 R_386_32   .L.str2
 // CHECK:     0x17 R_386_PC32 puts
 // CHECK:   }
 // CHECK: ]

test/MC/ELF/compression.s

@@ -38,7 +38,7 @@
 
 // In x86 32 bit named symbols are used for temporary symbols in merge
 // sections, so make sure we handle symbols inside compressed sections
-// 386-SYMBOLS-GNU: Name: .zdebug_str
+// 386-SYMBOLS-GNU: Name: .Linfo_string0
 // 386-SYMBOLS-GNU-NOT: }
 // 386-SYMBOLS-GNU: Section: .zdebug_str
 
@@ -73,7 +73,7 @@
 // ZLIB-STYLE-FLAGS32-NEXT: AddressAlignment: 4
 // ZLIB-STYLE-FLAGS64-NEXT: AddressAlignment: 8
 
-// 386-SYMBOLS-ZLIB: Name: .debug_str
+// 386-SYMBOLS-ZLIB: Name: .Linfo_string0
 // 386-SYMBOLS-ZLIB-NOT: }
 // 386-SYMBOLS-ZLIB: Section: .debug_str
 

test/MC/ELF/relocation-386.s

@@ -8,7 +8,7 @@
 // I386: Format: elf32-i386
 // CHECK:      Relocations [
 // CHECK-NEXT:   Section {{.*}} .rel.text {
-// CHECK-NEXT:     0x2          R_386_GOTOFF     .rodata.str1.16 0x0
+// CHECK-NEXT:     0x2          R_386_GOTOFF     .Lfoo 0x0
 // CHECK-NEXT:     0x{{[^ ]+}}  R_386_PLT32      bar2 0x0
 // CHECK-NEXT:     0x{{[^ ]+}}  R_386_GOTPC      _GLOBAL_OFFSET_TABLE_ 0x0
 // Relocation 3 (bar3@GOTOFF) is done with symbol 7 (bss)

test/MC/Mips/elf-relsym.s

@@ -4,10 +4,16 @@
 
 // CHECK: Symbols [
 // CHECK:   Symbol {
-// CHECK:     Name: .rodata.cst8
+// CHECK:     Name: $.str
 // CHECK:   }
 // CHECK:   Symbol {
-// CHECK:     Name: .rodata.str1.1
+// CHECK:     Name: $.str1
+// CHECK:   }
+// CHECK:   Symbol {
+// CHECK:     Name: $CPI0_0
+// CHECK:   }
+// CHECK:   Symbol {
+// CHECK:     Name: $CPI0_1
 // CHECK:   }
 // CHECK: ]
 

test/MC/Mips/xgot.s

@@ -10,8 +10,8 @@
 // CHECK:   0x1C R_MIPS_GOT_LO16 ext_1
 // CHECK:   0x24 R_MIPS_CALL_HI16 printf
 // CHECK:   0x30 R_MIPS_CALL_LO16 printf
-// CHECK:   0x2C R_MIPS_GOT16 .rodata.str1.1 0x0
-// CHECK:   0x38 R_MIPS_LO16 .rodata.str1.1 0x0
+// CHECK:   0x2C R_MIPS_GOT16 $.str
+// CHECK:   0x38 R_MIPS_LO16 $.str
 // CHECK: ]
 
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