[lld] Add infrastructure for handling RISCV vendor-specific relocations.

lld/ELF/Arch/RISCV.cpp

@@ -41,6 +41,8 @@ class RISCV final : public TargetInfo {
   RelType getDynRel(RelType type) const override;
   RelExpr getRelExpr(RelType type, const Symbol &s,
                      const uint8_t *loc) const override;
+  RelExpr getVendorRelExpr(RelType type, const Symbol &s, const uint8_t *loc,
+                           StringRef vendor) const override;
   void relocate(uint8_t *loc, const Relocation &rel,
                 uint64_t val) const override;
   void relocateAlloc(InputSectionBase &sec, uint8_t *buf) const override;
@@ -338,6 +340,8 @@ RelExpr RISCV::getRelExpr(const RelType type, const Symbol &s,
   case R_RISCV_SET_ULEB128:
   case R_RISCV_SUB_ULEB128:
     return RE_RISCV_LEB128;
+  case R_RISCV_VENDOR:
+    return R_NONE;
   default:
     Err(ctx) << getErrorLoc(ctx, loc) << "unknown relocation (" << type.v
              << ") against symbol " << &s;
@@ -555,6 +559,15 @@ void RISCV::relocate(uint8_t *loc, const Relocation &rel, uint64_t val) const {
   }
 }
 
+RelExpr RISCV::getVendorRelExpr(const RelType type, const Symbol &s,
+                                const uint8_t *loc, StringRef vendor) const {
+  // TODO: Dispatch to vendor-specific relocation handling.
+  Err(ctx) << getErrorLoc(ctx, loc) << "unknown vendor-specific relocation ("
+           << type.v << ") in vendor namespace \"" << vendor
+           << "\" against symbol " << &s;
+  return R_NONE;
+}
+
 static bool relaxable(ArrayRef<Relocation> relocs, size_t i) {
   return i + 1 != relocs.size() && relocs[i + 1].type == R_RISCV_RELAX;
 }

lld/ELF/Relocations.cpp

@@ -457,6 +457,7 @@ class RelocationScanner {
   Ctx &ctx;
   InputSectionBase *sec;
   OffsetGetter getter;
+  StringRef rvVendor;
 
   // End of relocations, used by Mips/PPC64.
   const void *end = nullptr;
@@ -1510,13 +1511,25 @@ void RelocationScanner::scanOne(typename Relocs<RelTy>::const_iterator &i) {
       ++i;
     }
   }
+
+  // Stash the RISCV vendor namespace for the subsequent relocation.
+  if (LLVM_UNLIKELY(ctx.arg.emachine == EM_RISCV && type == R_RISCV_VENDOR)) {
+    rvVendor = sym.getName();
+    return;
+  }
+
   // Get an offset in an output section this relocation is applied to.
   uint64_t offset = getter.get(ctx, rel.r_offset);
   if (offset == uint64_t(-1))
     return;
 
-  RelExpr expr =
-      ctx.target->getRelExpr(type, sym, sec->content().data() + offset);
+  RelExpr expr;
+  if (LLVM_LIKELY(rvVendor.empty())) {
+    expr = ctx.target->getRelExpr(type, sym, sec->content().data() + offset);
+  } else {
+    expr = ctx.target->getVendorRelExpr(
+        type, sym, sec->content().data() + offset, rvVendor);
+  }
   int64_t addend = RelTy::HasAddend
                        ? getAddend<ELFT>(rel)
                        : ctx.target->getImplicitAddend(
@@ -1526,6 +1539,9 @@ void RelocationScanner::scanOne(typename Relocs<RelTy>::const_iterator &i) {
   else if (ctx.arg.emachine == EM_PPC64 && ctx.arg.isPic && type == R_PPC64_TOC)
     addend += getPPC64TocBase(ctx);
 
+  // A RISCV vendor namespace only applies to a single relocation.
+  rvVendor = "";
+
   // Ignore R_*_NONE and other marker relocations.
   if (expr == R_NONE)
     return;

lld/ELF/Target.h

@@ -33,6 +33,11 @@ class TargetInfo {
   virtual uint32_t calcEFlags() const { return 0; }
   virtual RelExpr getRelExpr(RelType type, const Symbol &s,
                              const uint8_t *loc) const = 0;
+  virtual RelExpr getVendorRelExpr(RelType type, const Symbol &s,
+                                   const uint8_t *loc, StringRef vendor) const {
+    Err(ctx) << "target doesn't support vendor-specific relocations";
+    return R_NONE;
+  };
   virtual RelType getDynRel(RelType type) const { return 0; }
   virtual void writeGotPltHeader(uint8_t *buf) const {}
   virtual void writeGotHeader(uint8_t *buf) const {}

lld/test/ELF/riscv-vendor-relocations.s

@@ -0,0 +1,16 @@
+# RUN: llvm-mc -triple riscv32 %s -filetype=obj -o %t.o
+# RUN: not ld.lld -pie %t.o -o /dev/null 2>&1 | FileCheck %s
+
+  .option exact
+
+  .global TARGET
+TARGET:
+  nop
+
+.global INVALID_VENDOR
+.reloc 1f, R_RISCV_VENDOR, INVALID_VENDOR+0
+.reloc 1f, R_RISCV_CUSTOM255, TARGET
+1:
+  nop
+
+# CHECK: error: {{.*}} unknown vendor-specific relocation (255) in vendor namespace "INVALID_VENDOR" against symbol TARGET