[ELF2] Implement support for -discard-locals.

This is not on by default, but it may make sense to change it in future.

llvm-svn: 248133

lld/ELF/Config.h

@@ -21,6 +21,7 @@ struct Configuration {
   std::string RPath;
   bool Shared = false;
   bool DiscardAll = false;
+  bool DiscardLocals = false;
 };
 
 extern Configuration *Config;

lld/ELF/Driver.cpp

@@ -85,6 +85,9 @@ void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
   if (Args.hasArg(OPT_discard_all))
     Config->DiscardAll = true;
 
+  if (Args.hasArg(OPT_discard_locals))
+    Config->DiscardLocals = true;
+
   // Create a list of input files.
   std::vector<MemoryBufferRef> Inputs;
 

lld/ELF/Options.td

@@ -18,3 +18,6 @@ def shared : Flag<["-"], "shared">,
 
 def discard_all : Flag<["-"], "discard-all">,
      HelpText<"Delete all local symbols">;
+
+def discard_locals : Flag<["-"], "discard-locals">,
+     HelpText<"Delete temporary local symbols">;

lld/ELF/Writer.cpp

@@ -820,6 +820,8 @@ template <class ELFT> void SymbolTableSection<ELFT>::writeTo(uint8_t *Buf) {
         auto *ESym = reinterpret_cast<Elf_Sym *>(Buf);
         uint32_t SecIndex = Sym.st_shndx;
         ErrorOr<StringRef> SymName = Sym.getName(File.getStringTable());
+        if (Config->DiscardLocals && SymName->startswith(".L"))
+          continue;
         ESym->st_name = (SymName) ? StrTabSec.getFileOff(*SymName) : 0;
         ESym->st_size = Sym.st_size;
         ESym->setBindingAndType(Sym.getBinding(), Sym.getType());
@@ -1044,7 +1046,7 @@ template <class ELFT> void Writer<ELFT>::createSections() {
       Elf_Sym_Range Syms = File.getLocalSymbols();
       for (const Elf_Sym &Sym : Syms) {
         ErrorOr<StringRef> SymName = Sym.getName(File.getStringTable());
-        if (SymName)
+        if (SymName && !(Config->DiscardLocals && SymName->startswith(".L")))
           SymTabSec.addSymbol(*SymName, true);
       }
     }

lld/test/elf2/discard-locals.s

@@ -0,0 +1,52 @@
+// RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux -save-temp-labels %s -o %t
+// RUN: lld -flavor gnu2 -discard-locals %t -o %t2
+// RUN: llvm-readobj -s -sd -t %t2 | FileCheck %s
+// REQUIRES: x86
+
+.global _start
+_start:
+
+.text
+.Lmyvar:
+.Lmyothervar:
+
+// CHECK:   Section {
+// CHECK:     Name: .strtab
+// CHECK-NEXT:     Type: SHT_STRTAB
+// CHECK-NEXT:     Flags [
+// CHECK-NEXT:     ]
+// CHECK-NEXT:     Address:
+// CHECK-NEXT:     Offset:
+// CHECK-NEXT:     Size:
+// CHECK-NEXT:     Link:
+// CHECK-NEXT:     Info:
+// CHECK-NEXT:     AddressAlignment:
+// CHECK-NEXT:     EntrySize:
+// CHECK-NEXT:     SectionData (
+// CHECK-NEXT:       0000: 002E7465 7874005F 73746172 74002E62
+// CHECK-NEXT:       0010: 7373002E 73747274 6162002E 73796D74
+// CHECK-NEXT:       0020: 6162002E 64617461 00
+// CHECK-NEXT:     )
+// CHECK-NEXT:   }
+// CHECK-NEXT: ]
+
+// CHECK: Symbols [
+// CHECK-NEXT:   Symbol {
+// CHECK-NEXT:     Name:
+// CHECK-NEXT:     Value: 0x0
+// CHECK-NEXT:     Size: 0
+// CHECK-NEXT:     Binding: Local
+// CHECK-NEXT:     Type: None
+// CHECK-NEXT:     Other: 0
+// CHECK-NEXT:     Section: Undefined
+// CHECK-NEXT:   }
+// CHECK-NEXT:   Symbol {
+// CHECK-NEXT:     Name: _start
+// CHECK-NEXT:     Value: 0x11000
+// CHECK-NEXT:     Size: 0
+// CHECK-NEXT:     Binding: Global
+// CHECK-NEXT:     Type: None
+// CHECK-NEXT:     Other: 0
+// CHECK-NEXT:     Section: .text
+// CHECK-NEXT:   }
+// CHECk-NEXT: ]