[ELF] - Linkerscript: cleanup and introduce nextJoined().

[grimar]

Summary

Patch do 2 things:

1. It removes "section header name is empty" error. It looks not possible to get it. I think the only way to have Tok.empty() condition is when next() returns empty token because of error, in that case setError() will do nothing and itself useless.
2. There are cases when tokens can go in pairs, like "=0xFF" vs "= 0xFF". And we should handle combined and separate forms. I suggest to have some function like nextJoined() to proccess such cases to simplify parsing.

[ruiu]

ELF/LinkerScript.cpp

1658–1661

You removed this error check, so the real delta of this patch is -4 lines. That's probably too small to introduce a new convenient function.

[grimar]

ELF/LinkerScript.cpp

1658–1661

I know at least one more case when this function can be usefull.
If we are going to support assigning memory regions one day, it also exist in 2 forms in the wild scripts:

*(.text) } >rom
*(.text) } > rom

Probably there are other cases we do not know about yet.
Generally caller code looks more clean with it then without I think.

ELF/LinkerScript.cpp

else if (Tok == "SORT")
       readSort();
     else if (peek() == "(")
       Cmd->Commands.emplace_back(readInputSectionDescription(Tok));
     else
       setError("unknown command " + Tok);
   }
   Cmd->Phdrs = readOutputSectionPhdrs();
 
-  if (skip("="))
-    Cmd->Filler = readOutputSectionFiller(next());
-  else if (peek().startswith("="))
-    Cmd->Filler = readOutputSectionFiller(next().drop_front());
+  if (peek().startswith("="))
+    Cmd->Filler = readOutputSectionFiller(nextJoined());
 
   return Cmd;
 }
 
 // Read "=<number>" where <number> is an octal/decimal/hexadecimal number.
 // https://sourceware.org/binutils/docs/ld/Output-Section-Fill.html
 //
 // ld.gold is not fully compatible with ld.bfd. ld.bfd handles
Expr ScriptParser::readParenExpr() {
   expect("(");
   Expr E = readExpr();
   expect(")");
   return E;
 }
 
 std::vector<StringRef> ScriptParser::readOutputSectionPhdrs() {
   std::vector<StringRef> Phdrs;
-  while (!Error && peek().startswith(":")) {
-    StringRef Tok = next();
-    Tok = (Tok.size() == 1) ? next() : Tok.substr(1);
-    if (Tok.empty()) {
-      setError("section header name is empty");
-      break;
-    }
-    Phdrs.push_back(Tok);
-  }
+  while (!Error && peek().startswith(":"))
+    Phdrs.push_back(nextJoined());
   return Phdrs;
 }
 
 unsigned ScriptParser::readPhdrType() {
   StringRef Tok = next();
   unsigned Ret = StringSwitch<unsigned>(Tok)
                      .Case("PT_NULL", PT_NULL)
                      .Case("PT_LOAD", PT_LOAD)

ELF/ScriptParser.h

public:
   explicit ScriptParserBase(StringRef S) : Input(S), Tokens(tokenize(S)) {}
 
 protected:
   void setError(const Twine &Msg);
   static std::vector<StringRef> tokenize(StringRef S);
   static StringRef skipSpace(StringRef S);
   bool atEOF();
   StringRef next();
+  StringRef nextJoined();
   StringRef peek();
   bool skip(StringRef Tok);
   void expect(StringRef Expect);
 
   size_t getPos();
   void printErrorPos();
 
   StringRef Input;

ELF/ScriptParser.cpp

if (Error)
     return "";
   if (atEOF()) {
     setError("unexpected EOF");
     return "";
   }
   return Tokens[Pos++];
 }
 
+StringRef ScriptParserBase::nextJoined() {
+  StringRef Tok = next();
+  if (Tok.size() == 1)
+    return next();
+  return Tok.drop_front(std::min(Tok.size(), (size_t)1));
+}
+
 StringRef ScriptParserBase::peek() {
   StringRef Tok = next();
   if (Error)
     return "";
   --Pos;
   return Tok;
 }