[llvm] 6f95d33 - [ MC ] Match labels to existing fragments even when switching sections.
Michael Trent via llvm-commits
llvm-commits at lists.llvm.org
Wed Dec 18 09:58:37 PST 2019
Author: Michael Trent
Date: 2019-12-18T09:55:54-08:00
New Revision: 6f95d33e2b9e561e025f63b7a179b6e495f62c51
URL: https://github.com/llvm/llvm-project/commit/6f95d33e2b9e561e025f63b7a179b6e495f62c51
DIFF: https://github.com/llvm/llvm-project/commit/6f95d33e2b9e561e025f63b7a179b6e495f62c51.diff
LOG: [ MC ] Match labels to existing fragments even when switching sections.
(This commit restores the original branch (4272372c571) and applies an
additional change dropped from the original in a bad merge. This change
should address the previous bot failures. Both changes reviewed by pete.)
Summary:
This commit builds upon Derek Schuff's 2014 commit for attaching labels to
existing fragments ( Diff Revision: http://reviews.llvm.org/D5915 )
When temporary labels appear ahead of a fragment, MCObjectStreamer will
track the temporary label symbol in a "Pending Labels" list. Labels are
associated with fragments when a real fragment arrives; otherwise, an empty
data fragment will be created if the streamer's section changes or if the
stream finishes.
This commit moves the "Pending Labels" list into each MCStream, so that
this label-fragment matching process is resilient to section changes. If
the streamer emits a label in a new section, switches to another section to
do other work, then switches back to the first section and emits a
fragment, that initial label will be associated with this new fragment.
Labels will only receive empty data fragments in the case where no other
fragment exists for that section.
The downstream effects of this can be seen in Mach-O relocations. The
previous approach could produce local section relocations and external
symbol relocations for the same data in an object file, and this mix of
relocation types resulted in problems in the ld64 Mach-O linker. This
commit ensures relocations triggered by temporary labels are consistent.
Reviewers: pete, ab, dschuff
Reviewed By: pete, dschuff
Subscribers: hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D71368
Added:
llvm/test/MC/MachO/pending-labels.s
Modified:
llvm/include/llvm/MC/MCObjectStreamer.h
llvm/include/llvm/MC/MCSection.h
llvm/lib/MC/MCObjectStreamer.cpp
llvm/lib/MC/MCSection.cpp
Removed:
################################################################################
diff --git a/llvm/include/llvm/MC/MCObjectStreamer.h b/llvm/include/llvm/MC/MCObjectStreamer.h
index e10487988f6f..d8ea75a0ee7c 100644
--- a/llvm/include/llvm/MC/MCObjectStreamer.h
+++ b/llvm/include/llvm/MC/MCObjectStreamer.h
@@ -38,6 +38,8 @@ class MCObjectStreamer : public MCStreamer {
bool EmitEHFrame;
bool EmitDebugFrame;
SmallVector<MCSymbol *, 2> PendingLabels;
+ SmallVector<MCSection*, 2> PendingLabelSections;
+ unsigned CurSubsectionIdx;
struct PendingMCFixup {
const MCSymbol *Sym;
MCFixup Fixup;
@@ -87,17 +89,23 @@ class MCObjectStreamer : public MCStreamer {
protected:
bool changeSectionImpl(MCSection *Section, const MCExpr *Subsection);
- /// If any labels have been emitted but not assigned fragments, ensure that
- /// they get assigned, either to F if possible or to a new data fragment.
- /// Optionally, it is also possible to provide an offset \p FOffset, which
- /// will be used as a symbol offset within the fragment.
+ /// Assign a label to the current Section and Subsection even though a
+ /// fragment is not yet present. Use flushPendingLabels(F) to associate
+ /// a fragment with this label.
+ void addPendingLabel(MCSymbol* label);
+
+ /// If any labels have been emitted but not assigned fragments in the current
+ /// Section and Subsection, ensure that they get assigned, either to fragment
+ /// F if possible or to a new data fragment. Optionally, one can provide an
+ /// offset \p FOffset as a symbol offset within the fragment.
void flushPendingLabels(MCFragment *F, uint64_t FOffset = 0);
public:
void visitUsedSymbol(const MCSymbol &Sym) override;
- /// Create a dummy fragment to assign any pending labels.
- void flushPendingLabels() { flushPendingLabels(nullptr); }
+ /// Create a data fragment for any pending labels across all Sections
+ /// and Subsections.
+ void flushPendingLabels();
MCAssembler &getAssembler() { return *Assembler; }
MCAssembler *getAssemblerPtr() override;
diff --git a/llvm/include/llvm/MC/MCSection.h b/llvm/include/llvm/MC/MCSection.h
index d057feda87d8..c3535b6deaf3 100644
--- a/llvm/include/llvm/MC/MCSection.h
+++ b/llvm/include/llvm/MC/MCSection.h
@@ -92,6 +92,15 @@ class MCSection {
/// below that number.
SmallVector<std::pair<unsigned, MCFragment *>, 1> SubsectionFragmentMap;
+ /// State for tracking labels that don't yet have Fragments
+ struct PendingLabel {
+ MCSymbol* Sym;
+ unsigned Subsection;
+ PendingLabel(MCSymbol* Sym, unsigned Subsection = 0)
+ : Sym(Sym), Subsection(Subsection) {}
+ };
+ SmallVector<PendingLabel, 2> PendingLabels;
+
protected:
SectionVariant Variant;
SectionKind Kind;
@@ -187,6 +196,18 @@ class MCSection {
/// Check whether this section is "virtual", that is has no actual object
/// file contents.
virtual bool isVirtualSection() const = 0;
+
+ /// Add a pending label for the requested subsection. This label will be
+ /// associated with a fragment in flushPendingLabels()
+ void addPendingLabel(MCSymbol* label, unsigned Subsection = 0);
+
+ /// Associate all pending labels in a subsection with a fragment.
+ void flushPendingLabels(MCFragment *F, uint64_t FOffset = 0,
+ unsigned Subsection = 0);
+
+ /// Associate all pending labels with empty data fragments. One fragment
+ /// will be created for each subsection as necessary.
+ void flushPendingLabels();
};
} // end namespace llvm
diff --git a/llvm/lib/MC/MCObjectStreamer.cpp b/llvm/lib/MC/MCObjectStreamer.cpp
index 6c85f2296cfd..1ed6ec1015b2 100644
--- a/llvm/lib/MC/MCObjectStreamer.cpp
+++ b/llvm/lib/MC/MCObjectStreamer.cpp
@@ -42,20 +42,64 @@ MCAssembler *MCObjectStreamer::getAssemblerPtr() {
return nullptr;
}
+void MCObjectStreamer::addPendingLabel(MCSymbol* S) {
+ MCSection *CurSection = getCurrentSectionOnly();
+ if (CurSection) {
+ // Register labels that have not yet been assigned to a Section.
+ if (!PendingLabels.empty()) {
+ for (MCSymbol* Sym : PendingLabels)
+ CurSection->addPendingLabel(Sym);
+ PendingLabels.clear();
+ }
+
+ // Add this label to the current Section / Subsection.
+ CurSection->addPendingLabel(S, CurSubsectionIdx);
+
+ // Add this Section to the list of PendingLabelSections.
+ auto SecIt = std::find(PendingLabelSections.begin(),
+ PendingLabelSections.end(), CurSection);
+ if (SecIt == PendingLabelSections.end())
+ PendingLabelSections.push_back(CurSection);
+ }
+ else
+ // There is no Section / Subsection for this label yet.
+ PendingLabels.push_back(S);
+}
+
void MCObjectStreamer::flushPendingLabels(MCFragment *F, uint64_t FOffset) {
- if (PendingLabels.empty())
+ MCSection *CurSection = getCurrentSectionOnly();
+ if (!CurSection) {
+ assert(PendingLabels.empty());
return;
- if (!F) {
- F = new MCDataFragment();
- MCSection *CurSection = getCurrentSectionOnly();
- CurSection->getFragmentList().insert(CurInsertionPoint, F);
- F->setParent(CurSection);
}
- for (MCSymbol *Sym : PendingLabels) {
- Sym->setFragment(F);
- Sym->setOffset(FOffset);
+ // Register labels that have not yet been assigned to a Section.
+ if (!PendingLabels.empty()) {
+ for (MCSymbol* Sym : PendingLabels)
+ CurSection->addPendingLabel(Sym, CurSubsectionIdx);
+ PendingLabels.clear();
}
- PendingLabels.clear();
+
+ // Associate a fragment with this label, either the supplied fragment
+ // or an empty data fragment.
+ if (F)
+ CurSection->flushPendingLabels(F, FOffset, CurSubsectionIdx);
+ else
+ CurSection->flushPendingLabels(nullptr, 0, CurSubsectionIdx);
+}
+
+void MCObjectStreamer::flushPendingLabels() {
+ // Register labels that have not yet been assigned to a Section.
+ if (!PendingLabels.empty()) {
+ MCSection *CurSection = getCurrentSectionOnly();
+ assert(CurSection);
+ for (MCSymbol* Sym : PendingLabels)
+ CurSection->addPendingLabel(Sym, CurSubsectionIdx);
+ PendingLabels.clear();
+ }
+
+ // Assign an empty data fragment to all remaining pending labels.
+ for (MCSection* Section : PendingLabelSections)
+ Section->flushPendingLabels();
}
// When fixup's offset is a forward declared label, e.g.:
@@ -120,6 +164,7 @@ void MCObjectStreamer::reset() {
EmitEHFrame = true;
EmitDebugFrame = false;
PendingLabels.clear();
+ PendingLabelSections.clear();
MCStreamer::reset();
}
@@ -237,7 +282,7 @@ void MCObjectStreamer::EmitLabel(MCSymbol *Symbol, SMLoc Loc) {
// fragment. (They will all be reassigned to a real fragment in
// flushPendingLabels())
Symbol->setOffset(0);
- PendingLabels.push_back(Symbol);
+ addPendingLabel(Symbol);
}
}
@@ -257,7 +302,7 @@ void MCObjectStreamer::EmitLabelAtPos(MCSymbol *Symbol, SMLoc Loc,
assert(isa<MCDummyFragment>(F) &&
"F must either be an MCDataFragment or the pending MCDummyFragment");
assert(Offset == 0);
- PendingLabels.push_back(Symbol);
+ addPendingLabel(Symbol);
}
}
@@ -292,7 +337,6 @@ void MCObjectStreamer::ChangeSection(MCSection *Section,
bool MCObjectStreamer::changeSectionImpl(MCSection *Section,
const MCExpr *Subsection) {
assert(Section && "Cannot switch to a null section!");
- flushPendingLabels(nullptr);
getContext().clearDwarfLocSeen();
bool Created = getAssembler().registerSection(*Section);
@@ -303,8 +347,9 @@ bool MCObjectStreamer::changeSectionImpl(MCSection *Section,
report_fatal_error("Cannot evaluate subsection number");
if (IntSubsection < 0 || IntSubsection > 8192)
report_fatal_error("Subsection number out of range");
+ CurSubsectionIdx = unsigned(IntSubsection);
CurInsertionPoint =
- Section->getSubsectionInsertionPoint(unsigned(IntSubsection));
+ Section->getSubsectionInsertionPoint(CurSubsectionIdx);
return Created;
}
@@ -712,7 +757,9 @@ void MCObjectStreamer::FinishImpl() {
// Dump out the dwarf file & directory tables and line tables.
MCDwarfLineTable::Emit(this, getAssembler().getDWARFLinetableParams());
+ // Update any remaining pending labels with empty data fragments.
flushPendingLabels();
+
resolvePendingFixups();
getAssembler().Finish();
}
diff --git a/llvm/lib/MC/MCSection.cpp b/llvm/lib/MC/MCSection.cpp
index 2c892ab81608..7a953054e729 100644
--- a/llvm/lib/MC/MCSection.cpp
+++ b/llvm/lib/MC/MCSection.cpp
@@ -86,6 +86,41 @@ MCSection::getSubsectionInsertionPoint(unsigned Subsection) {
return IP;
}
+void MCSection::addPendingLabel(MCSymbol* label, unsigned Subsection) {
+ PendingLabels.push_back(PendingLabel(label, Subsection));
+}
+
+void MCSection::flushPendingLabels(MCFragment *F, uint64_t FOffset,
+ unsigned Subsection) {
+ if (PendingLabels.empty())
+ return;
+
+ // Set the fragment and fragment offset for all pending symbols in the
+ // specified Subsection, and remove those symbols from the pending list.
+ for (auto It = PendingLabels.begin(); It != PendingLabels.end(); ++It) {
+ PendingLabel& Label = *It;
+ if (Label.Subsection == Subsection) {
+ Label.Sym->setFragment(F);
+ Label.Sym->setOffset(FOffset);
+ PendingLabels.erase(It--);
+ }
+ }
+}
+
+void MCSection::flushPendingLabels() {
+ // Make sure all remaining pending labels point to data fragments, by
+ // creating new empty data fragments for each Subsection with labels pending.
+ while (!PendingLabels.empty()) {
+ PendingLabel& Label = PendingLabels[0];
+ iterator CurInsertionPoint =
+ this->getSubsectionInsertionPoint(Label.Subsection);
+ MCFragment *F = new MCDataFragment();
+ getFragmentList().insert(CurInsertionPoint, F);
+ F->setParent(this);
+ flushPendingLabels(F, 0, Label.Subsection);
+ }
+}
+
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD void MCSection::dump() const {
raw_ostream &OS = errs();
diff --git a/llvm/test/MC/MachO/pending-labels.s b/llvm/test/MC/MachO/pending-labels.s
new file mode 100644
index 000000000000..a4644357ca4e
--- /dev/null
+++ b/llvm/test/MC/MachO/pending-labels.s
@@ -0,0 +1,48 @@
+// Verify relocations for temporary labels are referenced by real symbols
+// at the same address.
+//
+// RUN: llvm-mc -triple x86_64-apple-darwin -filetype=obj -o - %s | llvm-objdump -r - | FileCheck %s
+
+L1:
+ .section __TEXT,__text_cold,regular,pure_instructions
+L2:
+ .text
+L3:
+ .section __TEXT,__text_cold,regular,pure_instructions
+L4:
+_function2:
+L5:
+ nop
+L6:
+ .text
+L7:
+_function1:
+L8:
+ nop
+
+ .data
+__data:
+ .quad L1-.
+ .quad L2-.
+ .quad L3-.
+ .quad L4-.
+ .quad L5-.
+ .quad L6-.
+ .quad L7-.
+ .quad L8-.
+// CHECK: 0000000000000038 X86_64_RELOC_SUBTRACTOR _function1-__data
+// CHECK: 0000000000000038 X86_64_RELOC_UNSIGNED _function1
+// CHECK: 0000000000000030 X86_64_RELOC_SUBTRACTOR _function1-__data
+// CHECK: 0000000000000030 X86_64_RELOC_UNSIGNED _function1
+// CHECK: 0000000000000028 X86_64_RELOC_SUBTRACTOR _function2-__data
+// CHECK: 0000000000000028 X86_64_RELOC_UNSIGNED _function2
+// CHECK: 0000000000000020 X86_64_RELOC_SUBTRACTOR _function2-__data
+// CHECK: 0000000000000020 X86_64_RELOC_UNSIGNED _function2
+// CHECK: 0000000000000018 X86_64_RELOC_SUBTRACTOR _function2-__data
+// CHECK: 0000000000000018 X86_64_RELOC_UNSIGNED _function2
+// CHECK: 0000000000000010 X86_64_RELOC_SUBTRACTOR _function1-__data
+// CHECK: 0000000000000010 X86_64_RELOC_UNSIGNED _function1
+// CHECK: 0000000000000008 X86_64_RELOC_SUBTRACTOR _function2-__data
+// CHECK: 0000000000000008 X86_64_RELOC_UNSIGNED _function2
+// CHECK: 0000000000000000 X86_64_RELOC_SUBTRACTOR _function1-__data
+// CHECK: 0000000000000000 X86_64_RELOC_UNSIGNED _function1
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