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

[via llvm-commits]

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@@ -887,30 +923,49 @@ Expected<uint64_t> ELFFile<ELFT>::getDynSymtabSize() const {
   return 0;
 }
 
-template <class ELFT> ELFFile<ELFT>::ELFFile(StringRef Object) : Buf(Object) {
+template <class ELFT> ELFFile<ELFT>::ELFFile(StringRef Object) : Buf(Object) {}
+
+template <class ELFT> Error ELFFile<ELFT>::readShdrZero() {
   const Elf_Ehdr &Header = getHeader();
-  RealPhNum = Header.e_phnum;
-  RealShNum = Header.e_shnum;
-  RealShStrNdx = Header.e_shstrndx;
-  if (!Header.hasPhdrNumExtension())
-    return;
 
-  // An ELF binary may report `hasExtendedHeader` as true but not actually
-  // include an extended header. For example, a core dump can contain 65,535
-  // segments but no sections at all. We defer reporting an error until section
-  // 0 is accessed. Consumers should handle and emit the error themselves when
-  // they attempt to access it.
-  auto SecOrErr = getSection(0);
-  if (!SecOrErr) {
-    consumeError(SecOrErr.takeError());
-    return;
+  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;
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aokblast wrote:

if we actually have sh_num == 0, and both phnum and shstrndx are valid. It should not be considered as an Error. Right? Since the search of shdr 0 is caused by shnum (not phnum or shstrndx) but we actually have 0 sections. For this case, we should not regard it as an error. 

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