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

[via llvm-commits]

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@@ -891,6 +927,38 @@ 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.
+    if (Header.e_shnum == 0)
+      RealShNum = 1;
+    else
+      RealShNum = Header.e_shnum;
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aokblast wrote:

This change is to reflect the following comment. I think I misunderstand something.
We need to read section 0 not only in e_shnum == 0 but also when e_phnum == PN_XNUM.

> This code should be guarded by an e_shnum == 0 check. If e_shnum != 0, we don't need to do funky things to read the index 0 header, like pre-filling RealShNum with a fake value, and can instead just set RealShNum to the right value up-front prior to calling sections().


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