PECOFF: Fix base relocation for ImageBase.

This is yet another edge case of base relocation for symbols. Absolute
symbols are in general not target of base relocation because absolute
atom is a way to point to a specific memory location. In r229816, I
removed entries for absolute atoms from the base relocation table
(so that they won't be fixed by the loader).

However, there was one exception -- ImageBase. ImageBase points to the
start address of the current image in memory. That needs to be fixed up
at load time. This patch is to treat the symbol in a special manner.

llvm-svn: 229961

1 files changed, 7 insertions, 1 deletions

diff --git a/lld/lib/ReaderWriter/PECOFF/WriterPECOFF.cpp b/lld/lib/ReaderWriter/PECOFF/WriterPECOFF.cpp
index 8dcfcc142a9..6459084d9e5 100644
--- a/lld/lib/ReaderWriter/PECOFF/WriterPECOFF.cpp
+++ b/lld/lib/ReaderWriter/PECOFF/WriterPECOFF.cpp
@@ -784,7 +784,13 @@ void AtomChunk::addBaseRelocations(BaseRelocationList &relocSites) const {
     for (const Reference *ref : *atom) {
       if (ref->kindNamespace() != Reference::KindNamespace::COFF)
         continue;
-      if (isa<AbsoluteAtom>(ref->target()))
+
+      // An absolute symbol points to a fixed location in memory. Their
+      // address should not be fixed at load time. One exception is ImageBase
+      // because that's relative to run-time image base address.
+      if (auto *abs = dyn_cast<AbsoluteAtom>(ref->target()))
+        if (!abs->name().equals("__ImageBase") &&
+            !abs->name().equals("___ImageBase"))
           continue;
 
       uint64_t address = layout->_virtualAddr + ref->offsetInAtom();