[ELF] Linkerscript: support hidden symbols assignments

[phosek]

Summary

This add support for HIDDEN command which can be used to define a symbol that will be hidden and won't be exported.

[phosek]

Just for reference, HIDDEN command is supported by both GNU linker and as of recently gold as well.

[ruiu]

ELF/LinkerScript.cpp

972

I'd change this function readProvideHidden(bool Provide, bool Hidden) and then

975–976

do

Cmd->Provide = Provide;
Cmd->Hidden = Hidden;

987–996

so that I can do

} else if (Tok == "PROVIDE"))
  Cmd = readProvideHidden(true, false);
} else if (Tok == "HIDDEN")) {
  Cmd = readProvideHidden(false, true);
} else if (Tok == "PROVIDE_HIDDEN")) {
  Cmd = readProvideHidden(true, true);
}

[ruiu]

LGTM

ELF/LinkerScript.cpp

private:
   OutputSectionCommand *readOutputSectionDescription(StringRef OutSec);
   std::vector<uint8_t> readOutputSectionFiller();
   std::vector<StringRef> readOutputSectionPhdrs();
   InputSectionDescription *readInputSectionDescription();
   std::vector<StringRef> readInputFilePatterns();
   InputSectionDescription *readInputSectionRules();
   unsigned readPhdrType();
   SortKind readSortKind();
-  SymbolAssignment *readProvide(bool Hidden);
+  SymbolAssignment *readProvideHidden(bool Provide, bool Hidden);
   SymbolAssignment *readProvideOrAssignment(StringRef Tok);
   Expr readAlign();
   void readSort();
   Expr readAssert();
 
   Expr readExpr();
   Expr readExpr1(Expr Lhs, int MinPrec);
   Expr readPrimary();
std::vector<uint8_t> ScriptParser::readOutputSectionFiller() {
   uint32_t V;
   if (Tok.substr(1).getAsInteger(0, V)) {
     setError("invalid filler expression: " + Tok);
     return {};
   }
   return { uint8_t(V >> 24), uint8_t(V >> 16), uint8_t(V >> 8), uint8_t(V) };
 }
 
-SymbolAssignment *ScriptParser::readProvide(bool Hidden) {
+SymbolAssignment *ScriptParser::readProvideHidden(bool Provide, bool Hidden) {
   expect("(");
   SymbolAssignment *Cmd = readAssignment(next());
-  Cmd->Provide = true;
+  Cmd->Provide = Provide;
   Cmd->Hidden = Hidden;
   expect(")");
   expect(";");
   return Cmd;
 }
 
 SymbolAssignment *ScriptParser::readProvideOrAssignment(StringRef Tok) {
   SymbolAssignment *Cmd = nullptr;
   if (peek() == "=" || peek() == "+=") {
     Cmd = readAssignment(Tok);
     expect(";");
   } else if (Tok == "PROVIDE") {
-    Cmd = readProvide(false);
+    Cmd = readProvideHidden(true, false);
+  } else if (Tok == "HIDDEN") {
+    Cmd = readProvideHidden(false, true);
   } else if (Tok == "PROVIDE_HIDDEN") {
-    Cmd = readProvide(true);
+    Cmd = readProvideHidden(true, true);
   }
   return Cmd;
 }
 
 static uint64_t getSymbolValue(StringRef S, uint64_t Dot) {
   if (S == ".")
     return Dot;
 
   switch (Config->EKind) {
   case ELF32LEKind:
     if (SymbolBody *B = Symtab<ELF32LE>::X->find(S))
       return B->getVA<ELF32LE>();

test/ELF/linkerscript/linkerscript-symbols.s

 
 # Provide existing symbol. The value should be 0, even though we
 # have value of 1 in PROVIDE_HIDDEN(). Visibility should not change
 # RUN: echo "SECTIONS { PROVIDE_HIDDEN(somesym = 1);}" > %t.script
 # RUN: ld.lld -o %t1 --script %t.script %t
 # RUN: llvm-objdump -t %t1 | FileCheck --check-prefix=HIDDEN2 %s
 # HIDDEN2: 0000000000000000         *ABS*    00000000 somesym
 
+# Hidden symbol assignment.
+# RUN: echo "SECTIONS { HIDDEN(newsym = 1);}" > %t.script
+# RUN: ld.lld -o %t1 --script %t.script %t
+# RUN: llvm-objdump -t %t1 | FileCheck --check-prefix=HIDDEN3 %s
+# HIDDEN3: 0000000000000001         *ABS*    00000000 .hidden newsym
+
 .global _start
 _start:
  nop
 
 .global somesym
 somesym = 0