[LLD] [COFF] Add support for a new, mingw specific embedded directive -exclude-symbols:

This is an entirely new embedded directive - extending the GNU ld
command line option --exclude-symbols to be usable in embedded
directives too.

(GNU ld.bfd also got support for the same new directive, currently in
the latest git version, after the 2.39 branch.)

This works as an inverse to the regular embedded dllexport directives,
for cases when autoexport of all eligible symbols is performed.

Differential Revision: https://reviews.llvm.org/D130120

Author: mstorsjo

lld/COFF/Driver.cpp

@@ -375,6 +375,14 @@ void LinkerDriver::parseDirectives(InputFile *file) {
   for (StringRef inc : directives.includes)
     addUndefined(inc);
 
+  // Handle /exclude-symbols: in bulk.
+  for (StringRef e : directives.excludes) {
+    SmallVector<StringRef, 2> vec;
+    e.split(vec, ',');
+    for (StringRef sym : vec)
+      excludedSymbols.insert(mangle(sym));
+  }
+
   // https://docs.microsoft.com/en-us/cpp/preprocessor/comment-c-cpp?view=msvc-160
   for (auto *arg : directives.args) {
     switch (arg->getOption().getID()) {
@@ -1309,7 +1317,7 @@ void LinkerDriver::maybeExportMinGWSymbols(const opt::InputArgList &args) {
       return;
   }
 
-  AutoExporter exporter;
+  AutoExporter exporter(excludedSymbols);
 
   for (auto *arg : args.filtered(OPT_wholearchive_file))
     if (Optional<StringRef> path = doFindFile(arg->getValue()))

lld/COFF/Driver.h

@@ -53,6 +53,7 @@ extern COFFOptTable optTable;
 struct ParsedDirectives {
   std::vector<StringRef> exports;
   std::vector<StringRef> includes;
+  std::vector<StringRef> excludes;
   llvm::opt::InputArgList args;
 };
 
@@ -159,6 +160,7 @@ class LinkerDriver {
   std::vector<MemoryBufferRef> resources;
 
   llvm::DenseSet<StringRef> directivesExports;
+  llvm::DenseSet<StringRef> excludedSymbols;
 
   COFFLinkerContext &ctx;
 

lld/COFF/DriverUtils.cpp

@@ -899,6 +899,9 @@ ParsedDirectives ArgParser::parseDirectives(StringRef s) {
     else if (tok.startswith_insensitive("/include:") ||
              tok.startswith_insensitive("-include:"))
       result.includes.push_back(tok.substr(strlen("/include:")));
+    else if (tok.startswith_insensitive("/exclude-symbols:") ||
+             tok.startswith_insensitive("-exclude-symbols:"))
+      result.excludes.push_back(tok.substr(strlen("/exclude-symbols:")));
     else {
       // Copy substrings that are not valid C strings. The tokenizer may have
       // already copied quoted arguments for us, so those do not need to be

lld/COFF/MinGW.cpp

@@ -23,7 +23,9 @@ using namespace llvm::COFF;
 using namespace lld;
 using namespace lld::coff;
 
-AutoExporter::AutoExporter() {
+AutoExporter::AutoExporter(
+    const llvm::DenseSet<StringRef> &manualExcludeSymbols)
+    : manualExcludeSymbols(manualExcludeSymbols) {
   excludeLibs = {
       "libgcc",
       "libgcc_s",
@@ -135,7 +137,7 @@ bool AutoExporter::shouldExport(const COFFLinkerContext &ctx,
   // disallow import symbols.
   if (!isa<DefinedRegular>(sym) && !isa<DefinedCommon>(sym))
     return false;
-  if (excludeSymbols.count(sym->getName()))
+  if (excludeSymbols.count(sym->getName()) || manualExcludeSymbols.count(sym->getName()))
     return false;
 
   for (StringRef prefix : excludeSymbolPrefixes.keys())

lld/COFF/MinGW.h

@@ -13,6 +13,7 @@
 #include "Symbols.h"
 #include "lld/Common/LLVM.h"
 #include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/StringSet.h"
 #include "llvm/Option/ArgList.h"
 #include <vector>
@@ -24,7 +25,7 @@ class COFFLinkerContext;
 // symbols for MinGW.
 class AutoExporter {
 public:
-  AutoExporter();
+  AutoExporter(const llvm::DenseSet<StringRef> &manualExcludeSymbols);
 
   void addWholeArchive(StringRef path);
   void addExcludedSymbol(StringRef symbol);
@@ -35,6 +36,8 @@ class AutoExporter {
   llvm::StringSet<> excludeLibs;
   llvm::StringSet<> excludeObjects;
 
+  const llvm::DenseSet<StringRef> &manualExcludeSymbols;
+
   bool shouldExport(const COFFLinkerContext &ctx, Defined *sym) const;
 };
 

lld/docs/ReleaseNotes.rst

@@ -42,6 +42,9 @@ MinGW Improvements
 * The ``--exclude-symbols`` option is now supported.
   (`D130118 <https://reviews.llvm.org/D130118>`_)
 
+* Support for an entirely new object file directive, ``-exclude-symbols:``,
+  has been implemented. (`D130120 <https://reviews.llvm.org/D130120>`_)
+
 MachO Improvements
 ------------------
 

lld/test/COFF/exclude-symbols-embedded.s

@@ -0,0 +1,24 @@
+// REQUIRES: x86
+// RUN: llvm-mc -filetype=obj -triple=i686-win32-gnu %s -o %t.o
+
+// RUN: lld-link -lldmingw -dll -out:%t.dll %t.o -noentry
+// RUN: llvm-readobj --coff-exports %t.dll | FileCheck --implicit-check-not=Name: %s
+
+// CHECK: Name:
+// CHECK: Name: sym1
+
+.global _sym1
+_sym1:
+  ret
+
+.global _sym2
+_sym2:
+  ret
+
+.global _sym3
+_sym3:
+  ret
+
+.section .drectve,"yn"
+.ascii " -exclude-symbols:sym2,unknownsym"
+.ascii " -exclude-symbols:unkonwnsym,sym3"