Make --export-dynamic-symbol to add undefined symbols even if --export-dynamic is given.

[ruiu]

Summary

This patch addresses a minor compatibility issue with GNU linkers.

[ruiu]

Previously, --export-dynamic-symbol was ignored completely if --export-dynamic was passed together.

lld/ELF/Driver.cpp

void LinkerDriver::readConfigs(opt::InputArgList &Args) {
   // Parses -dynamic-list and -export-dynamic-symbol. They make some
   // symbols private. Note that -export-dynamic takes precedence over them
   // as it says all symbols should be exported.
   if (!HasExportDynamic) {
     for (auto *Arg : Args.filtered(OPT_dynamic_list))
       if (Optional<MemoryBufferRef> Buffer = readFile(Arg->getValue()))
         readDynamicList(*Buffer);
 
-    for (auto *Arg : Args.filtered(OPT_export_dynamic_symbol)) {
+    for (auto *Arg : Args.filtered(OPT_export_dynamic_symbol))
       Config->DynamicList.push_back(
           {Arg->getValue(), /*IsExternCpp*/ false, /*HasWildcard*/ false});
-      Config->Undefined.push_back(Arg->getValue());
-    }
   }
 
+  // If --export-dynamic-symbol=foo is given and symbol foo is defined in
+  // an object file in an archive file, that object file should be pulled
+  // out and linked. (It doesn't have to behave like that from technical
+  // point of view, but this is needed for compatibility with GNU.)
+  for (auto *Arg : Args.filtered(OPT_export_dynamic_symbol))
+    Config->Undefined.push_back(Arg->getValue());
+
   for (auto *Arg : Args.filtered(OPT_version_script))
     if (Optional<MemoryBufferRef> Buffer = readFile(Arg->getValue()))
       readVersionScript(*Buffer);
 }
 
 // Some Config members do not directly correspond to any particular
 // command line options, but computed based on other Config values.
 // This function initialize such members. See Config.h for the details

lld/test/ELF/export-dynamic-symbol.s

 # REQUIRES: x86
 
 # RUN: rm -f %t.a
 # RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %S/Inputs/archive2.s -o %t1.o
 # RUN: llvm-ar rcs %t.a %t1.o
-
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t2.o
+
 # RUN: ld.lld -shared -o %t.so --export-dynamic-symbol foo %t.a %t2.o
+# RUN: llvm-readelf -dyn-symbols %t.so | FileCheck %s
 
+# RUN: ld.lld -shared -o %t.so --export-dynamic --export-dynamic-symbol foo %t.a %t2.o
 # RUN: llvm-readelf -dyn-symbols %t.so | FileCheck %s
+
 # CHECK: foo
 
 .global _start
 _start:
   nop