[llvm][llvm-objcopy] When outputting to binary don't output segments …

…that cover no sections

Sometimes LLD will produce a PT_LOAD segment that only covers the
headers (and covers no sections). GNU objcopy does not output the
segment contents for these sections. In particular this is an issue in
building magenta because the final link step for the kernel would
produce just such a PT_LOAD segment. This change is to support this case
and to match what GNU objcopy does in this case.

Patch by Jake Ehrlich

Differential Revision: https://reviews.llvm.org/D36196

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@310149 91177308-0d34-0410-b5e6-96231b3b80d8

test/tools/llvm-objcopy/sectionless-segment.test

@@ -0,0 +1,4 @@
+# RUN: llvm-objcopy -O binary %p/Inputs/pt-phdr.elf %t
+# RUN: wc -c < %t | FileCheck %s
+
+# CHECK: 4110

tools/llvm-objcopy/Object.cpp

@@ -354,7 +354,10 @@ template <class ELFT> size_t BinaryObject<ELFT>::totalSize() const {
 template <class ELFT>
 void BinaryObject<ELFT>::write(FileOutputBuffer &Out) const {
   for (auto &Segment : this->Segments) {
-    if (Segment->Type == llvm::ELF::PT_LOAD) {
+    // GNU objcopy does not output segments that do not cover a section. Such
+    // segments can sometimes be produced by LLD due to how LLD handles PT_PHDR.
+    if (Segment->Type == llvm::ELF::PT_LOAD &&
+        Segment->firstSection() != nullptr) {
       Segment->writeSegment(Out);
     }
   }
@@ -373,7 +376,8 @@ template <class ELFT> void BinaryObject<ELFT>::finalize() {
 
   uint64_t Offset = 0;
   for (auto &Segment : this->Segments) {
-    if (Segment->Type == llvm::ELF::PT_LOAD) {
+    if (Segment->Type == llvm::ELF::PT_LOAD &&
+        Segment->firstSection() != nullptr) {
       Offset = alignTo(Offset, Segment->Align);
       Segment->Offset = Offset;
       Offset += Segment->FileSize;