llvm · rlavaee · Jul 24, 2026
diff --git a/lld/ELF/Arch/X86_64.cpp b/lld/ELF/Arch/X86_64.cpp
@@ -576,6 +576,8 @@ RelExpr X86_64::getRelExpr(RelType type, const Symbol &s,
   case R_X86_64_PC32:
   case R_X86_64_PC64:
     return R_PC;
+  case R_X86_64_PCNEXT32:
+    return RE_X86_64_PCNEXT32;
   case R_X86_64_GOTOFF64:
     return R_GOTPLTREL;
   case R_X86_64_GOTPC32:
@@ -654,7 +656,7 @@ void X86_64::scanSectionImpl(InputSectionBase &sec, Relocs<RelTy> rels,
     Symbol &sym = sec.getFile<ELFT>()->getSymbol(symIdx);
     uint64_t offset = rel.r_offset;
     RelType type = rel.getType(false);
-    if (sym.isUndefined() && symIdx != 0 &&
+    if (sym.isUndefined() && symIdx != 0 && type != R_X86_64_PCNEXT32 &&
         rs.maybeReportUndefined(cast<Undefined>(sym), offset))
       continue;
     int64_t addend = rs.getAddend<ELFT>(rel, type);
@@ -682,6 +684,9 @@ void X86_64::scanSectionImpl(InputSectionBase &sec, Relocs<RelTy> rels,
     case R_X86_64_PC64:
       rs.processR_PC(type, offset, addend, sym);
       continue;
+    case R_X86_64_PCNEXT32:
+      rs.process(RE_X86_64_PCNEXT32, type, offset, sym, addend);
+      continue;
 
       // GOT-generating relocations:
     case R_X86_64_GOTPC32:
@@ -1182,6 +1187,7 @@ void X86_64::relocate(uint8_t *loc, const Relocation &rel, uint64_t val) const {
   case R_X86_64_GOTPC32:
   case R_X86_64_GOTPCREL:
   case R_X86_64_PC32:
+  case R_X86_64_PCNEXT32:
   case R_X86_64_PLT32:
   case R_X86_64_DTPOFF32:
   case R_X86_64_SIZE32:

diff --git a/lld/ELF/InputSection.cpp b/lld/ELF/InputSection.cpp
@@ -921,6 +921,10 @@ uint64_t InputSectionBase::getRelocTargetVA(Ctx &ctx, const Relocation &r,
   }
   case RE_LOONGARCH_PAGE_PC:
     return getLoongArchPageDelta(r.sym->getVA(ctx, a), p, r.type);
+  case RE_X86_64_PCNEXT32:
+    if (r.sym->isUndefined() || r.sym->isShared())
+      return 0;
+    return r.sym->getVA(ctx, a) - p;
   case R_PC:
   case RE_ARM_PCA: {
     uint64_t dest;

diff --git a/lld/ELF/Relocations.cpp b/lld/ELF/Relocations.cpp
@@ -846,7 +846,7 @@ bool RelocScan::isStaticLinkTimeConstant(RelExpr e, RelType type,
             R_GOTPLTONLY_PC, R_PLT_PC, R_PLT_GOTREL, R_PLT_GOTPLT,
             R_GOTPLT_GOTREL, R_GOTPLT_PC, RE_PPC32_PLTREL, RE_PPC64_CALL_PLT,
             RE_RISCV_ADD, RE_AARCH64_GOT_PAGE, RE_LOONGARCH_PLT_PAGE_PC,
-            RE_LOONGARCH_GOT, RE_LOONGARCH_GOT_PAGE_PC>(e))
+            RE_LOONGARCH_GOT, RE_LOONGARCH_GOT_PAGE_PC, RE_X86_64_PCNEXT32>(e))
     return true;
 
   // These never do, except if the entire file is position dependent or if

diff --git a/lld/ELF/Relocations.h b/lld/ELF/Relocations.h
@@ -126,6 +126,7 @@ enum RelExpr {
   RE_LOONGARCH_PC_INDIRECT,
   RE_LOONGARCH_TLSGD_PAGE_PC,
   RE_LOONGARCH_TLSDESC_PAGE_PC,
+  RE_X86_64_PCNEXT32,
 };
 
 // Architecture-neutral representation of relocation.

diff --git a/lld/test/ELF/x86-64-reloc-pcnext32.s b/lld/test/ELF/x86-64-reloc-pcnext32.s
@@ -0,0 +1,37 @@
+# REQUIRES: x86
+# RUN: rm -rf %t && split-file %s %t
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %t/so.s -o %t/so.o
+# RUN: ld.lld -shared %t/so.o -o %t/libso.so
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %t/main.s -o %t/main.o
+# RUN: ld.lld --image-base=0x1000 --section-start=.text=0x1000 %t/main.o %t/libso.so -o %t/out
+# RUN: llvm-readelf -x .text %t/out | FileCheck %s
+
+# CHECK: Hex dump of section '.text':
+# CHECK-NEXT: 0x00001000 0c000000 00000000 00000000 c3
+
+#--- so.s
+.global shared_sym
+shared_sym:
+  ret
+
+#--- main.s
+.globl _start
+_start:
+  # R_X86_64_PCNEXT32 to defined local symbol at 0x100c (place is 0x1000, 0x100c - 0x1000 = 0x0c)
+  .reloc ., R_X86_64_PCNEXT32, local_sym
+  .byte 0x00, 0x00, 0x00, 0x00
+
+  # R_X86_64_PCNEXT32 to shared symbol (resolves to 0)
+  .reloc ., R_X86_64_PCNEXT32, shared_sym
+  .byte 0x00, 0x00, 0x00, 0x00
+
+  # R_X86_64_PCNEXT32 to undefined weak symbol (resolves to 0)
+  .reloc ., R_X86_64_PCNEXT32, undef_sym
+  .byte 0x00, 0x00, 0x00, 0x00
+
+local_sym:
+  ret
+
+.weak undef_sym
diff --git a/llvm/docs/Extensions.md b/llvm/docs/Extensions.md
@@ -764,6 +764,17 @@ is also not the same as `cmpb $foo, %dil`, which is an 8-bit comparison.
 the assembler emits an `R_X86_64_GOTPCREL` relocation instead of a relaxable
 `R_X86_64[_REX]_GOTPCRELX` relocation.
 
+
+**@PCNEXT32** can be used on symbol references to indicate that the immediate
+operand is an offset to the target symbol from the next code location, causing
+the assembler to emit an `R_X86_64_PCNEXT32` relocation. If the target symbol
+is defined, the relocation resolves identically to `R_X86_64_PC32` (`S + A - P`).
+If the target symbol is undefined or in a shared library, it resolves to zero
+displacement (`0`) without generating a linker diagnostic. This allows
+undefined code prefetch targets (e.g. `prefetchit1 target@PCNEXT32(%rip)`) to
+gracefully degrade to a harmless prefetch of the immediately following
+instruction.
+
 ### Windows on ARM
 
 #### Stack Probe Emission

diff --git a/llvm/include/llvm/BinaryFormat/ELFRelocs/x86_64.def b/llvm/include/llvm/BinaryFormat/ELFRelocs/x86_64.def
@@ -46,4 +46,5 @@ ELF_RELOC(R_X86_64_REX_GOTPCRELX,    42)
 ELF_RELOC(R_X86_64_CODE_4_GOTPCRELX,    43)
 ELF_RELOC(R_X86_64_CODE_4_GOTTPOFF,    44)
 ELF_RELOC(R_X86_64_CODE_4_GOTPC32_TLSDESC,    45)
+ELF_RELOC(R_X86_64_PCNEXT32,                  46)
 ELF_RELOC(R_X86_64_CODE_6_GOTTPOFF,    50)
diff --git a/llvm/lib/Target/X86/MCTargetDesc/X86BaseInfo.h b/llvm/lib/Target/X86/MCTargetDesc/X86BaseInfo.h
@@ -394,6 +394,11 @@ enum TOF {
   /// See the X86-64 ELF ABI supplement for more details.
   ///    SYMBOL_LABEL @PLT
   MO_PLT,
+  /// MO_PCNEXT32 - On a symbol operand this indicates that the immediate is
+  /// offset to the prefetch target symbol name from the next code location.
+  /// If the target symbol is undefined, it will resolve to zero displacement.
+  ///    SYMBOL_LABEL @PCNEXT32
+  MO_PCNEXT32,
   /// MO_TLSGD - On a symbol operand this indicates that the immediate is
   /// the offset of the GOT entry with the TLS index structure that contains
   /// the module number and variable offset for the symbol. Used in the

diff --git a/llvm/lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp b/llvm/lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp
@@ -212,6 +212,9 @@ unsigned X86ELFObjectWriter::getRelocType64(SMLoc Loc, X86::Specifier Specifier,
   case X86::S_PLT:
     checkIs32(Loc, Type);
     return ELF::R_X86_64_PLT32;
+  case X86::S_PCNEXT32:
+    checkIs32(Loc, Type);
+    return ELF::R_X86_64_PCNEXT32;
   case X86::S_GOTPCREL:
     checkIs32(Loc, Type);
     // Older versions of ld.bfd/ld.gold/lld

diff --git a/llvm/lib/Target/X86/MCTargetDesc/X86MCAsmInfo.cpp b/llvm/lib/Target/X86/MCTargetDesc/X86MCAsmInfo.cpp
@@ -49,6 +49,7 @@ const MCAsmInfo::AtSpecifier atSpecifiers[] = {
     {X86::S_INDNTPOFF, "INDNTPOFF"},
     {MCSymbolRefExpr::VK_COFF_IMGREL32, "IMGREL"},
     {X86::S_NTPOFF, "NTPOFF"},
+    {X86::S_PCNEXT32, "PCNEXT32"},
     {X86::S_PCREL, "PCREL"},
     {X86::S_PLT, "PLT"},
     {X86::S_PLTOFF, "PLTOFF"},

diff --git a/llvm/lib/Target/X86/MCTargetDesc/X86MCAsmInfo.h b/llvm/lib/Target/X86/MCTargetDesc/X86MCAsmInfo.h
@@ -94,6 +94,7 @@ enum {
   S_GOTTPOFF,
   S_INDNTPOFF,
   S_NTPOFF,
+  S_PCNEXT32,
   S_PCREL,
   S_PLT,
   S_PLTOFF,

diff --git a/llvm/lib/Target/X86/X86AsmPrinter.cpp b/llvm/lib/Target/X86/X86AsmPrinter.cpp
@@ -332,6 +332,9 @@ void X86AsmPrinter::PrintSymbolOperand(const MachineOperand &MO,
   case X86II::MO_GOT:       O << "@GOT";       break;
   case X86II::MO_GOTOFF:    O << "@GOTOFF";    break;
   case X86II::MO_PLT:       O << "@PLT";       break;
+  case X86II::MO_PCNEXT32:
+    O << "@PCNEXT32";
+    break;
   case X86II::MO_TLVP:      O << "@TLVP";      break;
   case X86II::MO_TLVP_PIC_BASE:
     O << "@TLVP" << '-';

diff --git a/llvm/lib/Target/X86/X86MCInstLower.cpp b/llvm/lib/Target/X86/X86MCInstLower.cpp
@@ -301,6 +301,9 @@ MCOperand X86MCInstLower::LowerSymbolOperand(const MachineOperand &MO,
   case X86II::MO_PLT:
     Specifier = X86::S_PLT;
     break;
+  case X86II::MO_PCNEXT32:
+    Specifier = X86::S_PCNEXT32;
+    break;
   case X86II::MO_ABS8:
     Specifier = X86::S_ABS8;
     break;

diff --git a/llvm/test/MC/X86/elf-reloc-pcnext32.s b/llvm/test/MC/X86/elf-reloc-pcnext32.s
@@ -0,0 +1,11 @@
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %s | llvm-readobj -r - | FileCheck %s
+
+# CHECK:      Section ({{.*}}) .rela.text {
+# CHECK-NEXT:   0x3 R_X86_64_PCNEXT32 target 0xFFFFFFFFFFFFFFFC
+# CHECK-NEXT:   0x7 R_X86_64_PCNEXT32 target 0x0
+# CHECK-NEXT: }
+
+prefetchit1 target@PCNEXT32(%rip)
+
+.reloc ., R_X86_64_PCNEXT32, target
+.long 0