Drop prelink support.

The way prelink used to work was

* The compiler decides if a given section only has relocations that
are know to point to the same DSO. If so, it names it
.data.rel.ro.local<something>.
* The static linker puts all of these together.
* The prelinker program assigns addresses to each library and resolves
the local relocations.

There are many problems with this:
* It is incompatible with address space randomization.
* The information passed by the compiler is redundant. The linker
knows if a given relocation is in the same DSO or not. If could sort
by that if so desired.
* There are newer ways of speeding up DSO (gnu hash for example).
* Even if we want to implement this again in the compiler, the previous
  implementation is pretty broken. It talks about relocations that are
  "resolved by the static linker". If they are resolved, there are none
  left for the prelinker. What one needs to track is if an expression
  will require only dynamic relocations that point to the same DSO.

At this point it looks like the prelinker is an historical curiosity.
For example, fedora has retired it because it failed to build for two
releases
(http://pkgs.fedoraproject.org/cgit/prelink.git/commit/?id=eb43100a8331d91c801ee3dcdb0a0bb9babfdc1f)

This patch removes support for it. That is, it stops printing the
".local" sections.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@253280 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 5 insertions, 25 deletions

diff --git a/lib/Target/TargetLoweringObjectFile.cpp b/lib/Target/TargetLoweringObjectFile.cpp
index dd65b881f4d..5ccdae42024 100644
--- a/lib/Target/TargetLoweringObjectFile.cpp
+++ b/lib/Target/TargetLoweringObjectFile.cpp
@@ -169,14 +169,13 @@ SectionKind TargetLoweringObjectFile::getKindForGlobal(const GlobalValue *GV,
     // If the initializer for the global contains something that requires a
     // relocation, then we may have to drop this into a writable data section
     // even though it is marked const.
-    switch (C->getRelocationInfo()) {
-    case Constant::NoRelocation:
+    if (!C->needsRelocation()) {
       // If the global is required to have a unique address, it can't be put
       // into a mergable section: just drop it into the general read-only
       // section instead.
       if (!GVar->hasUnnamedAddr())
         return SectionKind::getReadOnly();
-        
+
       // If initializer is a null-terminated string, put it in a "cstring"
       // section of the right width.
       if (ArrayType *ATy = dyn_cast<ArrayType>(C->getType())) {
@@ -207,20 +206,7 @@ SectionKind TargetLoweringObjectFile::getKindForGlobal(const GlobalValue *GV,
         return SectionKind::getReadOnly();
       }
 
-    case Constant::LocalRelocation:
-      // In static relocation model, the linker will resolve all addresses, so
-      // the relocation entries will actually be constants by the time the app
-      // starts up.  However, we can't put this into a mergable section, because
-      // the linker doesn't take relocations into consideration when it tries to
-      // merge entries in the section.
-      if (ReloModel == Reloc::Static)
-        return SectionKind::getReadOnly();
-
-      // Otherwise, the dynamic linker needs to fix it up, put it in the
-      // writable data.rel.local section.
-      return SectionKind::getReadOnlyWithRelLocal();
-
-    case Constant::GlobalRelocations:
+    } else {
       // In static relocation model, the linker will resolve all addresses, so
       // the relocation entries will actually be constants by the time the app
       // starts up.  However, we can't put this into a mergable section, because
@@ -243,15 +229,9 @@ SectionKind TargetLoweringObjectFile::getKindForGlobal(const GlobalValue *GV,
   if (ReloModel == Reloc::Static)
     return SectionKind::getDataNoRel();
 
-  switch (C->getRelocationInfo()) {
-  case Constant::NoRelocation:
-    return SectionKind::getDataNoRel();
-  case Constant::LocalRelocation:
-    return SectionKind::getDataRelLocal();
-  case Constant::GlobalRelocations:
+  if (C->needsRelocation())
     return SectionKind::getDataRel();
-  }
-  llvm_unreachable("Invalid relocation");
+  return SectionKind::getDataNoRel();
 }
 
 /// This method computes the appropriate section to emit the specified global