[PATCH] D132262: RISCV: adjust relocation emission

[Saleem Abdulrasool via Phabricator via llvm-commits]

compnerd created this revision.
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https://reviews.llvm.org/D132262

Files:
  llvm/lib/Target/RISCV/MCTargetDesc/RISCVELFStreamer.cpp


Index: llvm/lib/Target/RISCV/MCTargetDesc/RISCVELFStreamer.cpp
===================================================================
--- llvm/lib/Target/RISCV/MCTargetDesc/RISCVELFStreamer.cpp
+++ llvm/lib/Target/RISCV/MCTargetDesc/RISCVELFStreamer.cpp
@@ -205,22 +205,14 @@
     }
   }
 
-  static bool requiresFixups(MCContext &C, const MCExpr *Value,
+  static bool requiresFixups(MCContext &C, MCDataFragment *F, const MCExpr *Val,
                              const MCExpr *&LHS, const MCExpr *&RHS) {
-    auto IsMetadataOrEHFrameSection = [](const MCSection &S) -> bool {
-      // Additionally check .apple_names/.apple_types. They are fixed-size and
-      // do not need fixups. llvm-dwarfdump --apple-names does not process
-      // R_RISCV_{ADD,SUB}32 in them.
-      return S.getKind().isMetadata() || S.getName() == ".eh_frame" ||
-             S.getName() == ".apple_names" || S.getName() == ".apple_types";
-    };
-
-    const auto *MBE = dyn_cast<MCBinaryExpr>(Value);
+    const auto *MBE = dyn_cast<MCBinaryExpr>(Val);
     if (MBE == nullptr)
       return false;
 
     MCValue E;
-    if (!Value->evaluateAsRelocatable(E, nullptr, nullptr))
+    if (!Val->evaluateAsRelocatable(E, nullptr, nullptr))
       return false;
     if (E.getSymA() == nullptr || E.getSymB() == nullptr)
       return false;
@@ -233,15 +225,25 @@
                              MCConstantExpr::create(E.getConstant(), C), C);
     RHS = E.getSymB();
 
-    // TODO: when available, R_RISCV_n_PCREL should be preferred.
+    // If either symbol is in a text section, we need to delay the relocation
+    // evaluation as relaxation may alter the size of the symbol.
+    //
+    // Unfortunately, we cannot identify if the symbol was built with relaxation
+    // as we do not track the state per symbol or section.  However, BFD will
+    // always emit the relocation and so we follow suit which avoids the need to
+    // track that information.
 
-    // Avoid pairwise relocations for symbolic difference in debug and .eh_frame
     if (A.isInSection())
-      return !IsMetadataOrEHFrameSection(A.getSection());
+      if (A.getSection().getKind().isText())
+        return true;
+
     if (B.isInSection())
-      return !IsMetadataOrEHFrameSection(B.getSection());
-    // as well as for absolute symbols.
-    return !A.getName().empty() || !B.getName().empty();
+      if (B.getSection().getKind().isText())
+        return true;
+
+    // Support cross-section difference ...
+    return A.isInSection() && B.isInSection() &&
+           A.getSection().getName() != B.getSection().getName();
   }
 
   void reset() override {
@@ -257,12 +259,13 @@
 
   void emitValueImpl(const MCExpr *Value, unsigned Size, SMLoc Loc) override {
     const MCExpr *A, *B;
-    if (!requiresFixups(getContext(), Value, A, B))
+    MCDataFragment *DF = getOrCreateDataFragment();
+
+    if (!requiresFixups(getContext(), DF, Value, A, B))
       return MCELFStreamer::emitValueImpl(Value, Size, Loc);
 
     MCStreamer::emitValueImpl(Value, Size, Loc);
 
-    MCDataFragment *DF = getOrCreateDataFragment();
     flushPendingLabels(DF, DF->getContents().size());
     MCDwarfLineEntry::make(this, getCurrentSectionOnly());
 


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