[lld] r309796 - [ELF] - Recommit r309252 "[ELF] - Fix missing relocation when linking executable with --unresolved-symbols=ignore-all"

[George Rimar via llvm-commits]

Author: grimar
Date: Wed Aug  2 00:51:08 2017
New Revision: 309796

URL: http://llvm.org/viewvc/llvm-project?rev=309796&view=rev
Log:
[ELF] - Recommit r309252 "[ELF] - Fix missing relocation when linking executable with --unresolved-symbols=ignore-all"

With fix for undefined weak symbols in executable.

Original commit message:
This is PR32112. Previously when we linked executable with 
--unresolved-symbols=ignore-all and undefined symbols, like:

_start:
callq und at PLT

we did not create relocations, though it looks in that case
we should delegate handling of such symbols to runtime linker,
hence should emit them. Patch fixes that.

Differential revision: https://reviews.llvm.org/D35724

Added:
    lld/trunk/test/ELF/executable-undefined-ignoreall.s
      - copied unchanged from r309257, lld/trunk/test/ELF/executable-undefined-ignoreall.s
    lld/trunk/test/ELF/executable-undefined-protected-ignoreall.s
      - copied unchanged from r309257, lld/trunk/test/ELF/executable-undefined-protected-ignoreall.s
Modified:
    lld/trunk/ELF/Symbols.cpp
    lld/trunk/test/ELF/no-inhibit-exec.s

Modified: lld/trunk/ELF/Symbols.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Symbols.cpp?rev=309796&r1=309795&r2=309796&view=diff
==============================================================================
--- lld/trunk/ELF/Symbols.cpp (original)
+++ lld/trunk/ELF/Symbols.cpp Wed Aug  2 00:51:08 2017
@@ -141,10 +141,6 @@ bool SymbolBody::isPreemptible() const {
   if (isShared())
     return !NeedsCopy && !NeedsPltAddr;
 
-  // That's all that can be preempted in a non-DSO.
-  if (!Config->Shared)
-    return false;
-
   // Only symbols that appear in dynsym can be preempted.
   if (!symbol()->includeInDynsym())
     return false;
@@ -153,6 +149,15 @@ bool SymbolBody::isPreemptible() const {
   if (symbol()->Visibility != STV_DEFAULT)
     return false;
 
+  // Undefined symbols in non-DSOs are usually just an error, so it
+  // doesn't matter whether we return true or false here. However, if
+  // -unresolved-symbols=ignore-all is specified, undefined symbols in
+  // executables are automatically exported so that the runtime linker
+  // can try to resolve them. In that case, they is preemptible. So, we
+  // return true for an undefined symbol in case the option is specified.
+  if (!Config->Shared)
+    return isUndefined();
+
   // -Bsymbolic means that definitions are not preempted.
   if (Config->Bsymbolic || (Config->BsymbolicFunctions && isFunc()))
     return !isDefined();
@@ -358,7 +363,7 @@ bool Symbol::includeInDynsym() const {
   if (computeBinding() == STB_LOCAL)
     return false;
   if (body()->isUndefined())
-    return Config->Shared;
+    return Config->Shared || !body()->symbol()->isWeak();
   return ExportDynamic || body()->isShared();
 }
 

Modified: lld/trunk/test/ELF/no-inhibit-exec.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/no-inhibit-exec.s?rev=309796&r1=309795&r2=309796&view=diff
==============================================================================
--- lld/trunk/test/ELF/no-inhibit-exec.s (original)
+++ lld/trunk/test/ELF/no-inhibit-exec.s Wed Aug  2 00:51:08 2017
@@ -2,11 +2,15 @@
 # RUN: not ld.lld %t -o %t2
 # RUN: ld.lld %t --noinhibit-exec -o %t2
 # RUN: llvm-objdump -d %t2 | FileCheck %s
+# RUN: llvm-readobj -r %t2 | FileCheck %s --check-prefix=RELOC
 # REQUIRES: x86
 
 # CHECK: Disassembly of section .text:
 # CHECK-NEXT: _start
-# CHECK-NEXT: 201000: {{.*}} callq -2101253
+# CHECK-NEXT: 201000: {{.*}} callq 0
+
+# RELOC:      Relocations [
+# RELOC-NEXT: ]
 
 # next code will not link without noinhibit-exec flag
 # because of undefined symbol _bar