Set DF_TEXTREL to executables that need text relocations.

Summary:
If an executable needs text relocations, it should be marked as such so
that the loader can prepare for text relocations. We currently create a
dummy segment with DT_TEXTREL for that purpose.

Generic ABI as of 2000 [1] mentioned that "Its [DT_TEXTREL's] use
has been superseded by the DF_TEXTREL flag". However, it's actually not
superseded even after 18 years. OpenBSD and musl recognize only DT_TEXTREL.
So we still need to set both.

[1] http://www.sco.com/developers/gabi/2000-07-17/ch5.dynamic.html

Reviewers: rafael

Subscribers: emaste, llvm-commits, arichardson

Differential Revision: https://reviews.llvm.org/D43920

llvm-svn: 326503

lld/ELF/SyntheticSections.cpp

@@ -1046,6 +1046,8 @@ template <class ELFT> void DynamicSection<ELFT>::finalizeContents() {
     DtFlags |= DF_ORIGIN;
     DtFlags1 |= DF_1_ORIGIN;
   }
+  if (!Config->ZText)
+    DtFlags |= DF_TEXTREL;
 
   if (DtFlags)
     addInt(DT_FLAGS, DtFlags);

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

@@ -18,17 +18,21 @@
 # CHECK-NEXT:      0x1010 R_X86_64_PC64 zed 0x0
 # CHECK-NEXT:    }
 # CHECK-NEXT:  ]
+
 # CHECK: DynamicSection [
-# CHECK: 0x0000000000000016 TEXTREL 0x0
+# CHECK:   FLAGS TEXTREL
+# CHECK:   TEXTREL 0x0
 
 # STATIC:      Relocations [
 # STATIC-NEXT:    Section {{.*}} .rela.dyn {
 # STATIC-NEXT:      0x201008 R_X86_64_64 bar 0x0
 # STATIC-NEXT:      0x201010 R_X86_64_PC64 zed 0x0
 # STATIC-NEXT:    }
 # STATIC-NEXT:  ]
+
 # STATIC: DynamicSection [
-# STATIC: 0x0000000000000016 TEXTREL 0x0
+# STATIC:   FLAGS TEXTREL
+# STATIC:   TEXTREL 0x0
 
 foo:
 .quad foo