[llvm] [Object,ELF] Implement PN_XNUM extension for program headers (PR #162288)

[via llvm-commits]

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@@ -891,6 +925,49 @@ Expected<uint64_t> ELFFile<ELFT>::getDynSymtabSize() const {
 
 template <class ELFT> ELFFile<ELFT>::ELFFile(StringRef Object) : Buf(Object) {}
 
+template <class ELFT> Error ELFFile<ELFT>::readShdrZero() {
+  const Elf_Ehdr &Header = getHeader();
+
+  if ((Header.e_phnum == ELF::PN_XNUM || Header.e_shnum == 0 ||
+       Header.e_shstrndx == ELF::SHN_XINDEX) &&
+      Header.e_shoff != 0) {
+
+    // Pretend we have section 0 or sections() would call getShNum and thus
+    // become an infinite recursion
+    RealShNum = 0;
+    auto SecsOrErr = sections();
+    if (!SecsOrErr) {
+      RealShNum = std::nullopt;
+      return SecsOrErr.takeError();
+    }
+
+    // We can really have 0 number of seciton
+    if ((*SecsOrErr).size() == 0) {
+      if (Header.e_phnum == ELF::PN_XNUM ||
+          Header.e_shstrndx == ELF::SHN_XINDEX) {
+        return createError("Unable to find Section 0");
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aokblast wrote:

I will create a test for this in my readobj patch.

https://github.com/llvm/llvm-project/pull/162288