[llvm] f5b5398 - [JITLink][RISCV] Ignore R_RISCV_RELAX and check R_RISCV_ALIGN

[Jonas Hahnfeld via llvm-commits]

Author: Jonas Hahnfeld
Date: 2022-07-06T18:09:19+02:00
New Revision: f5b5398ebf7da1ab54f6793331bca8fbc3340f14

URL: https://github.com/llvm/llvm-project/commit/f5b5398ebf7da1ab54f6793331bca8fbc3340f14
DIFF: https://github.com/llvm/llvm-project/commit/f5b5398ebf7da1ab54f6793331bca8fbc3340f14.diff

LOG: [JITLink][RISCV] Ignore R_RISCV_RELAX and check R_RISCV_ALIGN

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.

Differential Revision: https://reviews.llvm.org/D129159

Added: 
    

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

Removed: 
    


################################################################################
diff  --git a/llvm/lib/ExecutionEngine/JITLink/ELF_riscv.cpp b/llvm/lib/ExecutionEngine/JITLink/ELF_riscv.cpp
index 197ab71f52741..c7596efe2bb8c 100644
--- a/llvm/lib/ExecutionEngine/JITLink/ELF_riscv.cpp
+++ b/llvm/lib/ExecutionEngine/JITLink/ELF_riscv.cpp
@@ -494,6 +494,30 @@ class ELFLinkGraphBuilder_riscv : public ELFLinkGraphBuilder<ELFT> {
                             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 @@ class ELFLinkGraphBuilder_riscv : public ELFLinkGraphBuilder<ELFT> {
                   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);