[lld] 610a0e8 - [ELF] Assert on invalid GOT or PLT relocations

[Shoaib Meenai via llvm-commits]

Author: Shoaib Meenai
Date: 2022-04-20T10:46:04-07:00
New Revision: 610a0e8b5368853b0e67b16812c0fb61d8900356

URL: https://github.com/llvm/llvm-project/commit/610a0e8b5368853b0e67b16812c0fb61d8900356
DIFF: https://github.com/llvm/llvm-project/commit/610a0e8b5368853b0e67b16812c0fb61d8900356.diff

LOG: [ELF] Assert on invalid GOT or PLT relocations

Because of https://llvm.org/PR50675, we can end up producing a PLT
relocation referencing a symbol that's dropped from the dynamic symbol
table, which in turn causes a crash at runtime. We ran into this again
recently, resulting in crashes for our users. A subsequent diff will fix
that issue, but add an assert to catch it if it happens again.

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D123985

Added: 
    

Modified: 
    lld/ELF/SyntheticSections.cpp

Removed: 
    


################################################################################
diff  --git a/lld/ELF/SyntheticSections.cpp b/lld/ELF/SyntheticSections.cpp
index 4a07a4c95bdbd..07bb479d6b2d9 100644
--- a/lld/ELF/SyntheticSections.cpp
+++ b/lld/ELF/SyntheticSections.cpp
@@ -1589,9 +1589,13 @@ int64_t DynamicReloc::computeAddend() const {
 }
 
 uint32_t DynamicReloc::getSymIndex(SymbolTableBaseSection *symTab) const {
-  if (needsDynSymIndex())
-    return symTab->getSymbolIndex(sym);
-  return 0;
+  if (!needsDynSymIndex())
+    return 0;
+
+  size_t index = symTab->getSymbolIndex(sym);
+  assert((index != 0 || type != target->gotRel && type != target->pltRel) &&
+         "GOT or PLT relocation must refer to symbol in dynamic symbol table");
+  return index;
 }
 
 RelocationBaseSection::RelocationBaseSection(StringRef name, uint32_t type,