[PATCH] D129159: [JITLink][RISCV] Ignore R_RISCV_RELAX and check R_RISCV_ALIGN

[Jonas Hahnfeld via Phabricator via llvm-commits]

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It is fine to not implement and ignore linker relaxation for now, but
we need to check the alignment. Luckily, an alignment of only 2 bytes
is the most common case when interpreting C++ code in clang-repl, and
already guaranteed by the length of compressed instructions.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D129159

Files:
  llvm/lib/ExecutionEngine/JITLink/ELF_riscv.cpp


Index: llvm/lib/ExecutionEngine/JITLink/ELF_riscv.cpp
===================================================================
--- llvm/lib/ExecutionEngine/JITLink/ELF_riscv.cpp
+++ llvm/lib/ExecutionEngine/JITLink/ELF_riscv.cpp
@@ -494,6 +494,30 @@
                             Block &BlockToFix) {
     using Base = ELFLinkGraphBuilder<ELFT>;
 
+    uint32_t Type = Rel.getType(false);
+    // We do not implement linker relaxation, except what is required for
+    // alignment (see below).
+    if (Type == llvm::ELF::R_RISCV_RELAX)
+      return Error::success();
+
+    int64_t Addend = Rel.r_addend;
+    if (Type == llvm::ELF::R_RISCV_ALIGN) {
+      uint64_t Alignment = PowerOf2Ceil(Addend);
+      // FIXME: Implement support for ensuring alignment together with linker
+      // relaxation; 2 bytes are guaranteed by the length of compressed
+      // instructions, so this does not need any action from our side.
+      if (Alignment > 2)
+        return make_error<JITLinkError>(
+            formatv("Unsupported relocation R_RISCV_ALIGN with alignment {0} "
+                    "larger than 2 (addend: {1})",
+                    Alignment, Addend));
+      return Error::success();
+    }
+
+    Expected<riscv::EdgeKind_riscv> Kind = getRelocationKind(Type);
+    if (!Kind)
+      return Kind.takeError();
+
     uint32_t SymbolIndex = Rel.getSymbol(false);
     auto ObjSymbol = Base::Obj.getRelocationSymbol(Rel, Base::SymTabSec);
     if (!ObjSymbol)
@@ -508,12 +532,6 @@
                   Base::GraphSymbols.size()),
           inconvertibleErrorCode());
 
-    uint32_t Type = Rel.getType(false);
-    Expected<riscv::EdgeKind_riscv> Kind = getRelocationKind(Type);
-    if (!Kind)
-      return Kind.takeError();
-
-    int64_t Addend = Rel.r_addend;
     auto FixupAddress = orc::ExecutorAddr(FixupSect.sh_addr) + Rel.r_offset;
     Edge::OffsetT Offset = FixupAddress - BlockToFix.getAddress();
     Edge GE(*Kind, Offset, *GraphSymbol, Addend);


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