[ELF] - Proccess 'extern' keyword in version scripts.

[grimar]

Summary

During investigation about FreeBsd scripts I found that few of them uses
'extern' keyword. This patch just reads all globals inside as regular ones.

Note: I downloaded FreeBsd sources and tried to link with every *.map file in batch mode,
some of them are not script files, so I had to skip them manually.
Seems that this one in combination with D21556 allows to parse all available
FreeBsd version scripts.

[• rafael]

I am not sure it is a good idea to ignore these. 'extern "C++"' forces
the linker to match against mangled names. What is using it in freebsd
and what is it trying to match?

Cheers,
Rafael

[emaste]

Here is that script file: https://github.com/freebsd/freebsd/blob/master/gnu/lib/libsupc%2B%2B/Version.map

libsupc++ in the FreeBSD base system is only built on GCC-using architectures (e.g. MIPS). It isn't built in the default toolchain configuration for Tier-1 architectures and for current efforts using lld to link FreeBSD on x86 or arm we don't need to worry about this.

[grimar]

rL273426 was committed instead.

ELF/SymbolListFile.cpp

public:
   VersionScriptParser(StringRef S) : ScriptParserBase(S) {}
 
   void run();
 
 private:
   void parseVersion(StringRef Version);
   void parseLocal();
   void parseVersionSymbols(StringRef Version);
+  void parseExtern(StringRef Version);
 };
 
 void VersionScriptParser::parseVersion(StringRef Version) {
   expect("{");
   if (peek() == "global:") {
     next();
     parseVersionSymbols(Version);
   }
   if (peek() == "local:")
     parseLocal();
   else
     parseVersionSymbols(Version);
 
   expect("}");
   expect(";");
 }
 
 void VersionScriptParser::parseLocal() {
   expect("local:");
   expect("*");
   expect(";");
   Config->VersionScriptGlobalByDefault = false;
 }
 
+void VersionScriptParser::parseExtern(StringRef Version) {
+  expect("extern");
+  StringRef Lang = next();
+  if (Lang != "C" && Lang != "C++") {
+    setError("unsupported language " + Lang + " in extern scope");
+    return;
+  }
+  expect("{");
+  parseVersionSymbols(Version);
+  expect("}");
+  expect(";");
+}
+
 void VersionScriptParser::parseVersionSymbols(StringRef Version) {
   std::vector<StringRef> *Globals;
   if (Version.empty()) {
     Globals = &Config->VersionScriptGlobals;
   } else {
     Config->SymbolVersions.push_back(elf::Version(Version));
     Globals = &Config->SymbolVersions.back().Globals;
   }
 
   for (;;) {
     StringRef Cur = peek();
     if (Cur == "}" || Cur == "local:" || Error)
       return;
+    if (Cur == "extern") {
+      parseExtern(Version);
+      continue;
+    }
     next();
     Globals->push_back(Cur);
     expect(";");
   }
 }
 
 void VersionScriptParser::run() {
   StringRef Msg = "anonymous version definition is used in "

test/ELF/version-script-err.s

 // REQUIRES: x86
 
 // RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
 // RUN: not ld.lld -shared %t.o -o %t.so --version-script %p/Inputs/version-script-err.script 2>&1 | FileCheck %s
 // CHECK: ; expected, but got }
 
 // RUN: echo    "\"" > %terr1.script
 // RUN: not ld.lld --version-script %terr1.script -shared %t.o -o %t.so 2>&1 | \
 // RUN:   FileCheck -check-prefix=ERR1 %s
 // ERR1: unclosed quote
+
+// RUN: echo "VERSION { extern "C--" {}; }; " > %terr2.script
+// RUN: not ld.lld --version-script %terr2.script -shared %t.o -o %t.so 2>&1 | \
+// RUN:   FileCheck -check-prefix=ERR2 %s
+// ERR2: unsupported language C-- in extern scope

test/ELF/version-script-extern.s

+# REQUIRES: x86
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
+
+# RUN: echo "VERSION_1.0{      \
+# RUN:  extern "C++" {         \
+# RUN:    foo;                 \
+# RUN:    "bar";               \
+# RUN:  };                     \
+# RUN: }; " > %t1.script
+# RUN: ld.lld --version-script %t1.script -shared %t.o -o %t.so
+# RUN: llvm-readobj -dyn-symbols %t.so | FileCheck %s
+
+# CHECK: DynamicSymbols [
+# CHECK:   Symbol {
+# CHECK:     Name: bar@@VERSION_1.0
+# CHECK:   }
+# CHECK:   Symbol {
+# CHECK:     Name: foo@@VERSION_1.0
+# CHECK:   }
+# CHECK:   Symbol {
+# CHECK:     Name: zed@
+
+.global foo
+.type foo, @function
+foo:
+
+.global bar
+.type bar, @function
+bar:
+
+.global zed
+.type zed, @function
+zed: