[ELF] - Implemented -znotext

gold linker manual describes them as:

-z text	Do not permit relocations in read-only segments
-z notext Permit relocations in read-only segments (default)

In LLD default is to not permit them. Patch implements -z notext.

Differential revision: https://reviews.llvm.org/D30530

llvm-svn: 297366

lld/ELF/Config.h

@@ -142,6 +142,7 @@ struct Configuration {
   bool ZNow;
   bool ZOrigin;
   bool ZRelro;
+  bool ZText;
   bool ExitEarly;
   bool ZWxneeded;
   DiscardPolicy Discard;

lld/ELF/Driver.cpp

@@ -599,6 +599,7 @@ void LinkerDriver::readConfigs(opt::InputArgList &Args) {
   Config->ZOrigin = hasZOption(Args, "origin");
   Config->ZRelro = !hasZOption(Args, "norelro");
   Config->ZStackSize = getZOptionValue(Args, "stack-size", 0);
+  Config->ZText = !hasZOption(Args, "notext");
   Config->ZWxneeded = hasZOption(Args, "wxneeded");
 
   if (Config->LTOO > 3)

lld/ELF/Relocations.cpp

@@ -520,11 +520,12 @@ static RelExpr adjustExpr(const elf::ObjectFile<ELFT> &File, SymbolBody &Body,
   // only memory. We can hack around it if we are producing an executable and
   // the refered symbol can be preemepted to refer to the executable.
   if (Config->Shared || (Config->pic() && !isRelExpr(Expr))) {
-    error(S.getLocation<ELFT>(RelOff) + ": can't create dynamic relocation " +
-          toString(Type) + " against " +
-          (Body.getName().empty() ? "local symbol in readonly segment"
-                                  : "symbol '" + toString(Body) + "'") +
-          " defined in " + toString(Body.File));
+    if (Config->ZText)
+      error(S.getLocation<ELFT>(RelOff) + ": can't create dynamic relocation " +
+            toString(Type) + " against " +
+            (Body.getName().empty() ? "local symbol in readonly segment"
+                                    : "symbol '" + toString(Body) + "'") +
+            " defined in " + toString(Body.File));
     return Expr;
   }
   if (Body.getVisibility() != STV_DEFAULT) {

lld/ELF/SyntheticSections.cpp

@@ -1111,6 +1111,8 @@ template <class ELFT> void DynamicSection<ELFT>::finalizeContents() {
   add({DT_SYMENT, sizeof(Elf_Sym)});
   add({DT_STRTAB, In<ELFT>::DynStrTab});
   add({DT_STRSZ, In<ELFT>::DynStrTab->getSize()});
+  if (!Config->ZText)
+    add({DT_TEXTREL, (uint64_t)0});
   if (In<ELFT>::GnuHashTab)
     add({DT_GNU_HASH, In<ELFT>::GnuHashTab});
   if (In<ELFT>::HashTab)

lld/test/ELF/ztext-text-notext.s

@@ -0,0 +1,15 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
+# RUN: ld.lld -z notext %t.o -o %t -shared
+# RUN: llvm-readobj  -dynamic-table -r %t | FileCheck %s
+
+# CHECK:      Relocations [
+# CHECK-NEXT:    Section {{.*}} .rela.dyn {
+# CHECK-NEXT:      0x1000 R_X86_64_RELATIVE - 0x1000
+# CHECK-NEXT:    }
+# CHECK-NEXT:  ]
+# CHECK: DynamicSection [
+# CHECK: 0x0000000000000016 TEXTREL 0x0
+
+foo:
+.quad foo