[cheriot] Add an R_RISCV_CHERIOT_CCALL reloc

This is needed because Cheriot uses 11-bit shifts on AUIPCC (differing from normal RISC-V CHERI), and requires that the HI and LO relocs offset the target in the same direction. This is meant to be handled for all of Cheriot via R_RISCV_CHERIOT_COMPARTMENT_HI and R_RISCV_CHERIOT_COMPARTMENT_LO_I, but that is complicated by the simultaneous need to relax calls in (almost) all situations, which requires using R_RISCV_CHERI_CCALL. The solution is to add a new reloc that relaxes like R_RISCV_CHERI_CCALL, but relocates via R_RISCV_CHERIOT_COMPARTMENT_HI / R_RISCV_CHERIOT_COMPARTMENT_LO_I.

Author: resistor

lld/ELF/Arch/RISCV.cpp

@@ -358,6 +358,7 @@ RelExpr RISCV::getRelExpr(const RelType type, const Symbol &s,
   case R_RISCV_CALL:
   case R_RISCV_CALL_PLT:
   case R_RISCV_CHERI_CCALL:
+  case R_RISCV_CHERIOT_CCALL:
   case R_RISCV_PLT32:
     return R_PLT_PC;
   case R_RISCV_GOT_HI20:
@@ -504,6 +505,24 @@ void RISCV::relocate(uint8_t *loc, const Relocation &rel, uint64_t val) const {
     return;
   }
 
+  case R_RISCV_CHERIOT_CCALL: {
+    // Cheriot uses an 11-bit shift on AUIPCC, requiring different relocation
+    // compared to R_RISCV_CHERI_CCALL.
+    int64_t hi = SignExtend64(val + 0x800, bits) >> 12;
+    checkInt(loc, hi, 20, rel);
+    if (isInt<20>(hi)) {
+      relocate(loc,
+               Relocation{rel.expr, R_RISCV_CHERIOT_COMPARTMENT_HI, rel.offset,
+                          rel.addend, rel.sym},
+               val);
+      relocate(loc + 4,
+               Relocation{rel.expr, R_RISCV_CHERIOT_COMPARTMENT_LO_I,
+                          rel.offset, rel.addend, rel.sym},
+               val);
+    }
+    return;
+  }
+
   case R_RISCV_CHERI_CAPTAB_PCREL_HI20:
   case R_RISCV_CHERI_TLS_IE_CAPTAB_PCREL_HI20:
   case R_RISCV_CHERI_TLS_GD_CAPTAB_PCREL_HI20:
@@ -750,15 +769,15 @@ static void initSymbolAnchors() {
 }
 
 // Relax R_RISCV_CALL/R_RISCV_CALL_PLT auipc+jalr to c.j, c.jal, or jal.
-// Relax R_RISCV_CHERI_CCALL auipcc+cjalr to c.cj, c.cjal, or cjal.
+// Relax R_RISCV_CHERI[OT]_CCALL auipcc+cjalr to c.cj, c.cjal, or cjal.
 static void relaxCall(const InputSection &sec, size_t i, uint64_t loc,
                       Relocation &r, uint32_t &remove) {
   // We need to emit the correct relocations for CHERI, although the instruction
   // encodings are exactly the same with vanilla RISC-V.
-  auto jalRVCType = (r.type == R_RISCV_CHERI_CCALL) ? R_RISCV_CHERI_RVC_CJUMP
-                                                    : R_RISCV_RVC_JUMP;
-  auto jalType = (r.type == R_RISCV_CHERI_CCALL) ? R_RISCV_CHERI_CJAL
-                                                 : R_RISCV_JAL;
+  bool isCCall =
+      (r.type == R_RISCV_CHERI_CCALL) || (r.type == R_RISCV_CHERIOT_CCALL);
+  auto jalRVCType = (isCCall) ? R_RISCV_CHERI_RVC_CJUMP : R_RISCV_RVC_JUMP;
+  auto jalType = (isCCall) ? R_RISCV_CHERI_CJAL : R_RISCV_JAL;
   const bool rvc = config->eflags & EF_RISCV_RVC;
   const Symbol &sym = *r.sym;
   const uint64_t insnPair = read64le(sec.content().data() + r.offset);
@@ -967,6 +986,7 @@ static bool relax(InputSection &sec, int pass) {
     case R_RISCV_CALL:
     case R_RISCV_CALL_PLT:
     case R_RISCV_CHERI_CCALL:
+    case R_RISCV_CHERIOT_CCALL:
       if (i + 1 != sec.relocs().size() &&
           sec.relocs()[i + 1].type == R_RISCV_RELAX)
         relaxCall(sec, i, loc, r, remove);

llvm/include/llvm/BinaryFormat/ELFRelocs/RISCV.def

@@ -71,3 +71,4 @@ ELF_RELOC(R_RISCV_CHERIOT_COMPARTMENT_HI,    220)
 ELF_RELOC(R_RISCV_CHERIOT_COMPARTMENT_LO_I,  221)
 ELF_RELOC(R_RISCV_CHERIOT_COMPARTMENT_LO_S,  222)
 ELF_RELOC(R_RISCV_CHERIOT_COMPARTMENT_SIZE,  223)
+ELF_RELOC(R_RISCV_CHERIOT_CCALL,             224)

llvm/lib/Target/RISCV/MCTargetDesc/RISCVELFObjectWriter.cpp

@@ -13,6 +13,7 @@
 #include "llvm/MC/MCELFObjectWriter.h"
 #include "llvm/MC/MCFixup.h"
 #include "llvm/MC/MCObjectWriter.h"
+#include "llvm/MC/MCSubtargetInfo.h"
 #include "llvm/MC/MCValue.h"
 #include "llvm/Support/ErrorHandling.h"
 
@@ -97,8 +98,13 @@ unsigned RISCVELFObjectWriter::getRelocType(MCContext &Ctx,
       return ELF::R_RISCV_CHERI_TLS_GD_CAPTAB_PCREL_HI20;
     case RISCV::fixup_riscv_cjal:
       return ELF::R_RISCV_CHERI_CJAL;
-    case RISCV::fixup_riscv_ccall:
+    case RISCV::fixup_riscv_ccall: {
+      const auto *STI = Ctx.getSubtargetInfo();
+      if (STI->getCPU() == "cheriot" || STI->getTargetTriple().getSubArch() ==
+                                            Triple::RISCV32SubArch_cheriot_v1)
+        return ELF::R_RISCV_CHERIOT_CCALL;
       return ELF::R_RISCV_CHERI_CCALL;
+    }
     case RISCV::fixup_riscv_rvc_cjump:
       return ELF::R_RISCV_CHERI_RVC_CJUMP;
     case RISCV::fixup_riscv_add_8: