[BOLT] Add h4xx0r flag to skip updating program headers

[Amir]

Summary

-skip-phdr-rewrite FTW

[rafauler]

😂

bolt/lib/Rewrite/RewriteInstance.cpp

SkipFunctionNames("skip-funcs",
   cl::cat(BoltCategory));
 
 static cl::opt<std::string>
 SkipFunctionNamesFile("skip-funcs-file",
   cl::desc("file with list of functions to skip"),
   cl::Hidden,
   cl::cat(BoltCategory));
 
+static cl::opt<bool> SkipPhdrRewrite(
+    "skip-phdr-rewrite",
+    cl::desc("Developer use only: skip updating program headers"),
+    cl::ReallyHidden, cl::cat(BoltCategory));
+
 cl::opt<bool>
 TrapOldCode("trap-old-code",
   cl::desc("insert traps in old function bodies (relocation mode)"),
   cl::Hidden,
   cl::cat(BoltCategory));
 
 static cl::opt<std::string> DWPPathName("dwp",
                                         cl::desc("Path and name to DWP file."),

 }
 
 void RewriteInstance::updateOutputValues(const MCAsmLayout &Layout) {
   for (BinaryFunction *Function : BC->getAllBinaryFunctions())
     Function->updateOutputValues(Layout);
 }
 
 void RewriteInstance::patchELFPHDRTable() {
+  if (opts::SkipPhdrRewrite)
+    return;
+
   auto ELF64LEFile = cast<ELF64LEObjectFile>(InputFile);
   const ELFFile<ELF64LE> &Obj = ELF64LEFile->getELFFile();
   raw_fd_ostream &OS = Out->os();
 
   // Write/re-write program headers.
   Phnum = Obj.getHeader().e_phnum;
   if (PHDRTableOffset) {
     // Writing new pheader table and adding one new entry for R+X segment.