[BOLT][RISCV] Recognize mapping symbols

The RISC-V psABI [1] defines them similarly to AArch64.

[1] https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/master/riscv-elf.adoc#mapping-symbol

Reviewed By: yota9, Amir

Differential Revision: https://reviews.llvm.org/D153277

bolt/lib/Core/BinaryContext.cpp

@@ -1760,10 +1760,10 @@ void BinaryContext::printCFI(raw_ostream &OS, const MCCFIInstruction &Inst) {
 }
 
 MarkerSymType BinaryContext::getMarkerType(const SymbolRef &Symbol) const {
-  // For aarch64, the ABI defines mapping symbols so we identify data in the
-  // code section (see IHI0056B). $x identifies a symbol starting code or the
-  // end of a data chunk inside code, $d indentifies start of data.
-  if (!isAArch64() || ELFSymbolRef(Symbol).getSize())
+  // For aarch64 and riscv, the ABI defines mapping symbols so we identify data
+  // in the code section (see IHI0056B). $x identifies a symbol starting code or
+  // the end of a data chunk inside code, $d indentifies start of data.
+  if ((!isAArch64() && !isRISCV()) || ELFSymbolRef(Symbol).getSize())
     return MarkerSymType::NONE;
 
   Expected<StringRef> NameOrError = Symbol.getName();

bolt/lib/Rewrite/RewriteInstance.cpp

@@ -881,7 +881,7 @@ void RewriteInstance::discoverFileObjects() {
         }
       };
 
-  if (BC->isAArch64()) {
+  if (BC->isAArch64() || BC->isRISCV()) {
     addExtraDataMarkerPerSymbol(SortedFileSymbols, SortedMarkerSymbols);
     LastSymbol = std::stable_partition(
         SortedFileSymbols.begin(), SortedFileSymbols.end(),

bolt/test/RISCV/mapping-syms.s

@@ -0,0 +1,27 @@
+/// FIXME llvm-mc is used instead of clang because we need a recent change in
+/// the RISC-V MC layer (D153260). Once that one is released, we can switch to
+/// clang. (Note that the pre-merge check buildbots use the system's clang).
+// RUN: llvm-mc -triple riscv64 -mattr=+c -filetype obj -o %t.o %s
+// RUN: ld.lld -o %t %t.o
+// RUN: llvm-bolt --print-cfg --print-only=_start -o %t.bolt %t 2>&1 | FileCheck %s
+// RUN: llvm-objdump -d %t.bolt | FileCheck --check-prefix=CHECK-OBJDUMP %s
+
+// CHECK-NOT: BOLT-WARNING
+
+/// Check that .word is not disassembled by BOLT
+// CHECK: 00000000: nop
+// CHECK: 00000002: ret
+
+/// Check .word is still present in output
+// CHECK-OBJDUMP: <_start>:
+// CHECK-OBJDUMP-NEXT: nop
+// CHECK-OBJDUMP-NEXT: unimp
+// CHECK-OBJDUMP-NEXT: unimp
+// CHECK-OBJDUMP-NEXT: ret
+    .text
+    .globl _start
+    .p2align 1
+_start:
+    nop
+    .word 0x0
+    ret