[llvm-objcopy] Add support for nested and overlapping segments
This change adds support for nested and even overlapping segments. This means
that PT_PHDR, PT_GNU_RELRO, PT_TLS, and PT_DYNAMIC can be supported properly.
Differential Revision: https://reviews.llvm.org/D36558
llvm-svn: 313656
diff --git a/llvm/tools/llvm-objcopy/Object.cpp b/llvm/tools/llvm-objcopy/Object.cpp
index fd3add9..16bfdfd 100644
--- a/llvm/tools/llvm-objcopy/Object.cpp
+++ b/llvm/tools/llvm-objcopy/Object.cpp
@@ -240,6 +240,15 @@
Segment.Offset + Segment.FileSize >= Section.OriginalOffset + SecSize;
}
+// Returns true IFF a segment's original offset is inside of another segment's
+// range.
+static bool segmentOverlapsSegment(const Segment &Child,
+ const Segment &Parent) {
+
+ return Parent.OriginalOffset <= Child.OriginalOffset &&
+ Parent.OriginalOffset + Parent.FileSize > Child.OriginalOffset;
+}
+
template <class ELFT>
void Object<ELFT>::readProgramHeaders(const ELFFile<ELFT> &ElfFile) {
uint32_t Index = 0;
@@ -268,6 +277,30 @@
}
}
}
+ // Now we do an O(n^2) loop through the segments in order to match up
+ // segments.
+ for (auto &Child : Segments) {
+ for (auto &Parent : Segments) {
+ // Every segment will overlap with itself but we don't want a segment to
+ // be it's own parent so we avoid that situation.
+ if (&Child != &Parent && segmentOverlapsSegment(*Child, *Parent)) {
+ // We want a canonical "most parental" segment but this requires
+ // inspecting the ParentSegment.
+ if (Child->ParentSegment != nullptr) {
+ if (Child->ParentSegment->OriginalOffset > Parent->OriginalOffset) {
+ Child->ParentSegment = Parent.get();
+ } else if (Child->ParentSegment->Index > Parent->Index) {
+ // They must have equal OriginalOffsets so we need to disambiguate.
+ // To decide which is the parent we'll choose the one with the
+ // higher index.
+ Child->ParentSegment = Parent.get();
+ }
+ } else {
+ Child->ParentSegment = Parent.get();
+ }
+ }
+ }
+ }
}
template <class ELFT>
@@ -497,13 +530,30 @@
}
template <class ELFT> void ELFObject<ELFT>::assignOffsets() {
+ // We need a temporary list of segments that has a special order to it
+ // so that we know that anytime ->ParentSegment is set that segment has
+ // already had it's offset properly set.
+ std::vector<Segment *> OrderedSegments;
+ for (auto &Segment : this->Segments)
+ OrderedSegments.push_back(Segment.get());
+ auto CompareSegments = [](const Segment *A, const Segment *B) {
+ // Any segment without a parent segment should come before a segment
+ // that has a parent segment.
+ if (A->OriginalOffset < B->OriginalOffset)
+ return true;
+ if (A->OriginalOffset > B->OriginalOffset)
+ return false;
+ return A->Index < B->Index;
+ };
+ std::stable_sort(std::begin(OrderedSegments), std::end(OrderedSegments),
+ CompareSegments);
// The size of ELF + program headers will not change so it is ok to assume
// that the first offset of the first segment is a good place to start
// outputting sections. This covers both the standard case and the PT_PHDR
// case.
uint64_t Offset;
- if (!this->Segments.empty()) {
- Offset = this->Segments[0]->Offset;
+ if (!OrderedSegments.empty()) {
+ Offset = OrderedSegments[0]->Offset;
} else {
Offset = sizeof(Elf_Ehdr);
}
@@ -512,10 +562,20 @@
// then it's acceptable, but not ideal, to simply move it to after the
// segments. So we can simply layout segments one after the other accounting
// for alignment.
- for (auto &Segment : this->Segments) {
- Offset = alignTo(Offset, Segment->Align);
- Segment->Offset = Offset;
- Offset += Segment->FileSize;
+ for (auto &Segment : OrderedSegments) {
+ // We assume that segments have been ordered by OriginalOffset and Index
+ // such that a parent segment will always come before a child segment in
+ // OrderedSegments. This means that the Offset of the ParentSegment should
+ // already be set and we can set our offset relative to it.
+ if (Segment->ParentSegment != nullptr) {
+ auto Parent = Segment->ParentSegment;
+ Segment->Offset =
+ Parent->Offset + Segment->OriginalOffset - Parent->OriginalOffset;
+ } else {
+ Offset = alignTo(Offset, Segment->Align == 0 ? 1 : Segment->Align);
+ Segment->Offset = Offset;
+ Offset += Segment->FileSize;
+ }
}
// Now the offset of every segment has been set we can assign the offsets
// of each section. For sections that are covered by a segment we should use