[lld] r268558 - Don't produce relative relocs to ro segments.

[Rafael Espindola via llvm-commits]

Author: rafael
Date: Wed May  4 16:40:07 2016
New Revision: 268558

URL: http://llvm.org/viewvc/llvm-project?rev=268558&view=rev
Log:
Don't produce relative relocs to ro segments.

We were already checking for non relative relocations.

If we ever decide to add support for rw text segments this means we will
have a single spot to add the flag.

Added:
    lld/trunk/test/ELF/dynamic-reloc-in-ro.s
Modified:
    lld/trunk/ELF/Target.cpp
    lld/trunk/ELF/Writer.cpp

Modified: lld/trunk/ELF/Target.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Target.cpp?rev=268558&r1=268557&r2=268558&view=diff
==============================================================================
--- lld/trunk/ELF/Target.cpp (original)
+++ lld/trunk/ELF/Target.cpp Wed May  4 16:40:07 2016
@@ -976,6 +976,7 @@ bool AArch64TargetInfo::usesOnlyLowPageB
   case R_AARCH64_LDST64_ABS_LO12_NC:
   case R_AARCH64_LDST128_ABS_LO12_NC:
   case R_AARCH64_LD64_GOT_LO12_NC:
+  case R_AARCH64_TLSIE_LD64_GOTTPREL_LO12_NC:
     return true;
   }
 }

Modified: lld/trunk/ELF/Writer.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=268558&r1=268557&r2=268558&view=diff
==============================================================================
--- lld/trunk/ELF/Writer.cpp (original)
+++ lld/trunk/ELF/Writer.cpp Wed May  4 16:40:07 2016
@@ -442,14 +442,25 @@ static bool needsPlt(RelExpr Expr) {
 template <class ELFT>
 static bool isStaticLinkTimeConstant(RelExpr E, uint32_t Type,
                                      const SymbolBody &Body) {
-  if (E == R_SIZE)
+  // These expressions always compute a constant
+  if (E == R_SIZE || E == R_GOT_FROM_END || E == R_GOT_OFF || E == R_MIPS_GOT ||
+      E == R_MIPS_GOT_LOCAL || E == R_GOT_PAGE_PC || E == R_GOT_PC ||
+      E == R_PLT_PC || E == R_TLSGD_PC || E == R_TLSGD || E == R_PPC_PLT_OPD)
     return true;
 
-  bool AbsVal = (isAbsolute<ELFT>(Body) || Body.isTls()) &&
-                !refersToGotEntry(E) && !needsPlt(E);
+  // These never do, except if the entire file is position dependent or if
+  // only the low bits are used.
+  if (E == R_GOT || E == R_PLT)
+    return Target->usesOnlyLowPageBits(Type) || !Config->Pic;
 
-  bool RelE = E == R_PC || E == R_PLT_PC || E == R_GOT_PC || E == R_GOTREL ||
-              E == R_PAGE_PC;
+  if (Body.isPreemptible())
+    return false;
+
+  if (!Config->Pic)
+    return true;
+
+  bool AbsVal = isAbsolute<ELFT>(Body) || Body.isTls();
+  bool RelE = E == R_PC || E == R_GOTREL || E == R_PAGE_PC;
   if (AbsVal && !RelE)
     return true;
   if (!AbsVal && RelE)
@@ -497,16 +508,13 @@ static RelExpr fromPlt(RelExpr Expr) {
 template <class ELFT>
 RelExpr Writer<ELFT>::adjustExpr(SymbolBody &Body, bool IsWrite, RelExpr Expr,
                                  uint32_t Type) {
-  if (Body.isGnuIFunc())
-    return toPlt(Expr);
   bool Preemptible = Body.isPreemptible();
-  if (needsPlt(Expr)) {
-    if (Preemptible)
-      return Expr;
-    return fromPlt(Expr);
-  }
+  if (Body.isGnuIFunc())
+    Expr = toPlt(Expr);
+  else if (needsPlt(Expr) && !Preemptible)
+    Expr = fromPlt(Expr);
 
-  if (IsWrite || refersToGotEntry(Expr) || needsPlt(Expr) || !Preemptible)
+  if (IsWrite || isStaticLinkTimeConstant<ELFT>(Expr, Type, Body))
     return Expr;
 
   // This relocation would require the dynamic linker to write a value to read

Added: lld/trunk/test/ELF/dynamic-reloc-in-ro.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/dynamic-reloc-in-ro.s?rev=268558&view=auto
==============================================================================
--- lld/trunk/test/ELF/dynamic-reloc-in-ro.s (added)
+++ lld/trunk/test/ELF/dynamic-reloc-in-ro.s Wed May  4 16:40:07 2016
@@ -0,0 +1,8 @@
+// REQUIRES: x86
+// RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
+// RUN: not ld.lld %t.o -o %t.so -shared 2>&1 | FileCheck %s
+
+foo:
+.quad foo
+
+// CHECK: relocation R_X86_64_64 cannot be used when making a shared object; recompile with -fPIC.