[llvm] [llvm-objdump][ELF]Fix crash when reading strings from .dynstr(#86612) (PR #125679)

[Fangrui Song via llvm-commits]

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@@ -221,6 +224,20 @@ template <class ELFT> void ELFDumper<ELFT>::printDynamicSection() {
   std::string TagFmt = "  %-" + std::to_string(MaxLen) + "s ";
 
   outs() << "\nDynamic Section:\n";
+  auto StringTableSize = (typename ELFT::Xword)0;
+  for (const auto &Sec : cantFail(Elf.sections())) {
+    if (Sec.sh_type == ELF::SHT_STRTAB)
+      StringTableSize =
+          StringTableSize < Sec.sh_size ? Sec.sh_size : StringTableSize;
+  }
+  for (const typename ELFT::Dyn &Dyn : DynamicEntries) {
+    if (Dyn.d_tag == ELF::DT_STRSZ) {
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MaskRay wrote:

The section header table is optional in loadable units (executables, shared objects). Dynamic loaders only read dynamic tags, not the section header table. The dynamic tags are source of truths for the dynamic symbol table size. You can keep just the DT_STRSZ code and ignore `SHT_STRTAB`. 

We could emit a warning when the two values mismatch, but llvm-readobj doesn't do it. For the purpose of fixing just this crash it may not be necessary to add the warning.

https://github.com/llvm/llvm-project/pull/125679