Add TARGET(foo) linker script directive.

GNU ld's manual says that TARGET(foo) is basically an alias for
`--format foo` where foo is a BFD target name such as elf64-x86-64.

Unlike GNU linkers, lld doesn't allow arbitrary BFD target name for
--format. We accept only "default", "elf" or "binary". This makes
situation a bit tricky because we can't simply make TARGET an alias for
--target.

A quick code search revealed that the usage number of TARGET is very
small, and the only meaningful usage is to switch to the binary mode.
Thus, in this patch, we handle only TARGET(elf.*) and TARGET(binary).

Differential Revision: https://reviews.llvm.org/D48153

llvm-svn: 339060

lld/ELF/ScriptParser.cpp

@@ -72,6 +72,7 @@ private:
   void readRegionAlias();
   void readSearchDir();
   void readSections();
+  void readTarget();
   void readVersion();
   void readVersionScriptCommand();
 
@@ -255,6 +256,8 @@ void ScriptParser::readLinkerScript() {
       readSearchDir();
     } else if (Tok == "SECTIONS") {
       readSections();
+    } else if (Tok == "TARGET") {
+      readTarget();
     } else if (Tok == "VERSION") {
       readVersion();
     } else if (SymbolAssignment *Cmd = readAssignment(Tok)) {
@@ -522,6 +525,23 @@ void ScriptParser::readSections() {
                                  V.end());
 }
 
+void ScriptParser::readTarget() {
+  // TARGET(foo) is an alias for "--format foo". Unlike GNU linkers,
+  // we accept only a limited set of BFD names (i.e. "elf" or "binary")
+  // for --format. We recognize only /^elf/ and "binary" in the linker
+  // script as well.
+  expect("(");
+  StringRef Tok = next();
+  expect(")");
+
+  if (Tok.startswith("elf"))
+    Config->FormatBinary = false;
+  else if (Tok == "binary")
+    Config->FormatBinary = true;
+  else
+    setError("unknown target: " + Tok);
+}
+
 static int precedence(StringRef Op) {
   return StringSwitch<int>(Op)
       .Cases("*", "/", "%", 8)