[ELF][llvm-objcopy] Reject duplicate SHT_SYMTAB sections

The gABI prohibits multiple SH_SYMTAB sections. As a result,
llvm-objcopy was crashing in SymbolTableSection::removeSymbols(). This
patch fixes the issue by emitting an error if multiple SH_SYMTAB
sections are encountered when building an ELF object.

Fixes: https://github.com/llvm/llvm-project/issues/60448

Differential Revision: https://reviews.llvm.org/D143508

llvm/lib/ObjCopy/ELF/ELFObject.cpp

@@ -1704,6 +1704,10 @@ Expected<SectionBase &> ELFBuilder<ELFT>::makeSection(const Elf_Shdr &Shdr) {
     else
       return Data.takeError();
   case SHT_SYMTAB: {
+    // Multiple SHT_SYMTAB sections are forbidden by the ELF gABI.
+    if (Obj.SymbolTable != nullptr)
+      return createStringError(llvm::errc::invalid_argument,
+                               "found multiple SHT_SYMTAB sections");
     auto &SymTab = Obj.addSection<SymbolTableSection>();
     Obj.SymbolTable = &SymTab;
     return SymTab;

llvm/test/tools/llvm-objcopy/ELF/multiple-symtab.test

@@ -0,0 +1,20 @@
+## According to the ELF gABI, "Currently, an object file may have only one
+## section of each type [SHT_SYMTAB and SHT_DYNSYM], but this restriction may be
+## relaxed in the future."
+## This test shows that we emit an error if we encounter multiple SHT_SYMTAB
+## sections.
+# RUN: yaml2obj %s -o %t
+# RUN: not llvm-objcopy %t /dev/null 2>&1 | FileCheck %s
+
+# CHECK: error: found multiple SHT_SYMTAB sections
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_REL
+Sections:
+  - Name: .symtab
+    Type: SHT_SYMTAB
+  - Name: .symtab2
+    Type: SHT_SYMTAB