[RISCV] Vendor Relocations for Xqci extension (#135400)

This patch implements vendor relocation support for RISC-V, starting
with the Xqci extensions.

Vendor Relocations need to emit the vendor symbol, and add an
`R_RISCV_VENDOR` relocation against that symbol before the specific
vendor relocation itself.

This patch adds a `maybeAddVendorReloc` function which is called from
`addReloc`, to implement this functionality. Vendor identifier symbols
are cached, so that at most one is emitted per vendor identifier.

Vendor identifiers symbols do not interfere with identically named
symbols used by assembly.

Co-authored-by: Sam Elliott <quic_aelliott@quicinc.com>

Author: svs-quic

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

@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "RISCVAsmBackend.h"
+#include "RISCVFixupKinds.h"
 #include "RISCVMCExpr.h"
 #include "llvm/ADT/APInt.h"
 #include "llvm/MC/MCAsmInfo.h"
@@ -611,6 +612,46 @@ bool RISCVAsmBackend::evaluateTargetFixup(const MCFixup &Fixup,
          isPCRelFixupResolved(AUIPCTarget.getAddSym(), *AUIPCDF);
 }
 
+void RISCVAsmBackend::maybeAddVendorReloc(const MCFragment &F,
+                                          const MCFixup &Fixup) {
+  StringRef VendorIdentifier;
+  switch (Fixup.getTargetKind()) {
+  default:
+    // No Vendor Relocation Required.
+    return;
+  case RISCV::fixup_riscv_qc_e_branch:
+  case RISCV::fixup_riscv_qc_abs20_u:
+  case RISCV::fixup_riscv_qc_e_32:
+  case RISCV::fixup_riscv_qc_e_jump_plt:
+    VendorIdentifier = "QUALCOMM";
+    break;
+  }
+
+  // Create a local symbol for the vendor relocation to reference. It's fine if
+  // the symbol has the same name as an existing symbol.
+  MCContext &Ctx = Asm->getContext();
+  MCSymbol *VendorSymbol = Ctx.createLocalSymbol(VendorIdentifier);
+  auto [It, Inserted] =
+      VendorSymbols.try_emplace(VendorIdentifier, VendorSymbol);
+
+  if (Inserted) {
+    // Setup the just-created symbol
+    VendorSymbol->setVariableValue(MCConstantExpr::create(0, Ctx));
+    Asm->registerSymbol(*VendorSymbol);
+  } else {
+    // Fetch the existing symbol
+    VendorSymbol = It->getValue();
+  }
+
+  MCFixup VendorFixup =
+      MCFixup::create(Fixup.getOffset(), nullptr, ELF::R_RISCV_VENDOR);
+  // Explicitly create MCValue rather than using an MCExpr and evaluating it so
+  // that the absolute vendor symbol is not evaluated to constant 0.
+  MCValue VendorTarget = MCValue::get(VendorSymbol);
+  uint64_t VendorValue;
+  Asm->getWriter().recordRelocation(F, VendorFixup, VendorTarget, VendorValue);
+}
+
 bool RISCVAsmBackend::addReloc(const MCFragment &F, const MCFixup &Fixup,
                                const MCValue &Target, uint64_t &FixedValue,
                                bool IsResolved) {
@@ -660,7 +701,14 @@ bool RISCVAsmBackend::addReloc(const MCFragment &F, const MCFixup &Fixup,
   if (IsResolved &&
       (getFixupKindInfo(Fixup.getKind()).Flags & MCFixupKindInfo::FKF_IsPCRel))
     IsResolved = isPCRelFixupResolved(Target.getAddSym(), F);
-  IsResolved = MCAsmBackend::addReloc(F, Fixup, Target, FixedValue, IsResolved);
+
+  if (!IsResolved) {
+    // Some Fixups require a vendor relocation, record it (directly) before we
+    // add the relocation.
+    maybeAddVendorReloc(F, Fixup);
+
+    Asm->getWriter().recordRelocation(F, Fixup, Target, FixedValue);
+  }
 
   if (Fixup.isLinkerRelaxable()) {
     auto FA = MCFixup::create(Fixup.getOffset(), nullptr, ELF::R_RISCV_RELAX);

llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.h

@@ -12,6 +12,7 @@
 #include "MCTargetDesc/RISCVBaseInfo.h"
 #include "MCTargetDesc/RISCVFixupKinds.h"
 #include "MCTargetDesc/RISCVMCTargetDesc.h"
+#include "llvm/ADT/StringMap.h"
 #include "llvm/MC/MCAsmBackend.h"
 #include "llvm/MC/MCFixupKindInfo.h"
 #include "llvm/MC/MCSubtargetInfo.h"
@@ -31,6 +32,8 @@ class RISCVAsmBackend : public MCAsmBackend {
 
   bool isPCRelFixupResolved(const MCSymbol *SymA, const MCFragment &F);
 
+  StringMap<MCSymbol *> VendorSymbols;
+
 public:
   RISCVAsmBackend(const MCSubtargetInfo &STI, uint8_t OSABI, bool Is64Bit,
                   const MCTargetOptions &Options);
@@ -50,6 +53,8 @@ class RISCVAsmBackend : public MCAsmBackend {
   bool addReloc(const MCFragment &, const MCFixup &, const MCValue &,
                 uint64_t &FixedValue, bool IsResolved) override;
 
+  void maybeAddVendorReloc(const MCFragment &, const MCFixup &);
+
   void applyFixup(const MCFragment &, const MCFixup &, const MCValue &Target,
                   MutableArrayRef<char> Data, uint64_t Value,
                   bool IsResolved) override;

llvm/test/MC/RISCV/vendor-symbol.s

@@ -0,0 +1,35 @@
+# RUN: llvm-mc -triple riscv32 -mattr=+experimental-xqcibi %s \
+# RUN:     -filetype=obj -o - \
+# RUN:     | llvm-readelf -sr - \
+# RUN:     | FileCheck %s
+
+
+## This checks that the vendor identifier symbols required for vendor
+## relocations do not interfere with symbols with identical names that
+## are written in assembly.
+
+  .option exact
+
+  qc.e.bgeui s0, 20, QUALCOMM
+
+  .global QUALCOMM
+QUALCOMM:
+  nop
+
+  qc.e.bgeui s0, 20, QUALCOMM
+
+
+# CHECK-LABEL: Relocation section '.rela.text'
+## Note the different values for the "Sym. Value" Field
+# CHECK: R_RISCV_VENDOR    00000000 QUALCOMM + 0
+# CHECK: R_RISCV_CUSTOM193 00000006 QUALCOMM + 0
+# CHECK: R_RISCV_VENDOR    00000000 QUALCOMM + 0
+# CHECK: R_RISCV_CUSTOM193 00000006 QUALCOMM + 0
+
+
+# CHECK-LABEL: Symbol table '.symtab'
+# CHECK-NOT: QUALCOMM
+# CHECK: 00000000 0 NOTYPE  LOCAL  DEFAULT ABS QUALCOMM
+# CHECK-NOT: QUALCOMM
+# CHECK: 00000006 0 NOTYPE  GLOBAL DEFAULT   2 QUALCOMM
+# CHECK-NOT: QUALCOMM

llvm/test/MC/RISCV/xqcibi-relocations.s

@@ -1,38 +1,83 @@
-# RUN: llvm-mc -triple riscv32 -mattr=+experimental-xqcibi %s -show-encoding \
-# RUN:     | FileCheck -check-prefix=INSTR %s
-# RUN: llvm-mc -filetype=obj -triple riscv32 -mattr=+experimental-xqcibi %s -o %t.o
-# RUN: llvm-readobj -r %t.o | FileCheck -check-prefix=RELOC %s
+# RUN: llvm-mc -triple riscv32 -mattr=+experimental-xqcibi %s \
+# RUN:     | FileCheck -check-prefix=ASM %s
+# RUN: llvm-mc -triple riscv32 -mattr=+experimental-xqcibi %s \
+# RUN:     -filetype=obj -o - \
+# RUN:     | llvm-objdump -dr --mattr=+experimental-xqcibi - \
+# RUN:     | FileCheck -check-prefix=OBJ %s
 
-# Check prefixes:
-# RELOC - Check the relocation in the object.
-# INSTR - Check the instruction is handled properly by the ASMPrinter.
+## This test checks that we emit the right relocations for Xqcibi
+## relative branches. These can be resolved within the same section
+## (when relaxations are disabled) but otherwise require a relocation.
+## The QC.E.B<op>I instructions also require a vendor relocation.
 
-.text
+# This is required so that the conditional branches requiring relocations
+# are not converted into inverted branches with long jumps by the assembler.
+.option exact
 
-# Since foo is undefined, this will be relaxed to (qc.beqi + jal)
-qc.bnei x6, 10, foo
-# RELOC: R_RISCV_JAL foo 0x0
-# INSTR: qc.bnei t1, 10, foo
+# ASM-LABEL: this_section:
+# OBJ-LABEL: <this_section>:
+this_section:
 
-# Since foo is undefined, this will be relaxed to (qc.e.bltui + jal)
-qc.e.bgeui x8, 12, foo
-# RELOC: R_RISCV_JAL foo 0x0
-# INSTR: qc.e.bgeui s0, 12, foo
+# ASM: qc.bnei t1, 10, undef
+# OBJ: qc.bnei t1, 0xa, 0x0 <this_section>
+# OBJ-NEXT: R_RISCV_BRANCH undef{{$}}
+qc.bnei t1, 10, undef
 
-# Check that a label in a different section is handled similar to an undefined
-# symbol and gets relaxed to (qc.e.bgeui + jal)
-qc.e.bltui x4, 9, .bar
-# RELOC: R_RISCV_JAL .bar 0x0
-# INSTR: qc.e.bltui tp, 9, .bar
+# ASM: qc.e.bgeui s0, 20, undef
+# OBJ-NEXT: qc.e.bgeui s0, 0x14, 0x4 <this_section+0x4>
+# OBJ-NEXT: R_RISCV_VENDOR QUALCOMM{{$}}
+# OBJ-NEXT: R_RISCV_CUSTOM193 undef{{$}}
+qc.e.bgeui s0, 20, undef
 
-# Check that branches to a defined symbol are handled correctly
-qc.e.beqi x7, 8, .L1
-# INSTR: qc.e.beqi t2, 8, .L1
 
-.L1:
-  ret
+# ASM: qc.bnei t2, 11, same_section
+# OBJ-NEXT: qc.bnei t2, 0xb, 0x28 <same_section>
+qc.bnei t2, 11, same_section
 
-.section .t2
+# ASM: qc.e.bgeui s1, 21, same_section
+# OBJ-NEXT: qc.e.bgeui s1, 0x15, 0x28 <same_section>
+qc.e.bgeui s1, 21, same_section
 
-.bar:
-  ret
+
+# ASM: qc.bnei t2, 12, same_section_extern
+# OBJ-NEXT: qc.bnei t2, 0xc, 0x14 <this_section+0x14>
+# OBJ-NEXT: R_RISCV_BRANCH same_section_extern{{$}}
+qc.bnei t2, 12, same_section_extern
+
+# ASM: qc.e.bgeui s1, 22, same_section_extern
+# OBJ-NEXT: qc.e.bgeui s1, 0x16, 0x18 <this_section+0x18>
+# OBJ-NEXT: R_RISCV_VENDOR QUALCOMM{{$}}
+# OBJ-NEXT: R_RISCV_CUSTOM193 same_section_extern{{$}}
+qc.e.bgeui s1, 22, same_section_extern
+
+
+# ASM: qc.bnei t3, 13, other_section
+# OBJ-NEXT: qc.bnei t3, 0xd, 0x1e <this_section+0x1e>
+# OBJ-NEXT: R_RISCV_BRANCH other_section{{$}}
+qc.bnei t3, 13, other_section
+
+# ASM: qc.e.bgeui s2, 23, other_section
+# OBJ-NEXT: qc.e.bgeui s2, 0x17, 0x22 <this_section+0x22>
+# OBJ-NEXT: R_RISCV_VENDOR QUALCOMM{{$}}
+# OBJ-NEXT: R_RISCV_CUSTOM193 other_section{{$}}
+qc.e.bgeui s2, 23, other_section
+
+
+# ASM-LABEL: same_section:
+# OBJ-LABEL: <same_section>:
+same_section:
+  nop
+
+# ASM-LABEL: same_section_extern:
+# OBJ-LABEL: <same_section_extern>:
+  .global same_section_extern
+same_section_extern:
+  nop
+
+
+.section .text.second, "ax", @progbits
+
+# ASM-LABEL: other_section:
+# OBJ-LABEL: <other_section>:
+other_section:
+  nop

llvm/test/MC/RISCV/xqcilb-relocations.s

@@ -1,46 +1,84 @@
-# RUN: llvm-mc -triple riscv32 -mattr=+experimental-xqcilb %s -show-encoding \
-# RUN:     | FileCheck -check-prefix=INSTR %s
-# RUN: llvm-mc -filetype=obj -triple riscv32 -mattr=+experimental-xqcilb %s -o %t.o
-# RUN: llvm-readobj -r %t.o | FileCheck -check-prefix=RELOC %s
+# RUN: llvm-mc -triple riscv32 -mattr=+experimental-xqcilb %s \
+# RUN:     | FileCheck -check-prefix=ASM %s
+# RUN: llvm-mc -triple riscv32 -mattr=+experimental-xqcilb %s \
+# RUN:     -filetype=obj -o - \
+# RUN:     | llvm-objdump -dr --mattr=+experimental-xqcilb - \
+# RUN:     | FileCheck -check-prefix=OBJ %s
 
-# Check prefixes:
-# RELOC - Check the relocation in the object.
-# INSTR - Check the instruction is handled properly by the ASMPrinter.
-
-.text
+## This test checks that we emit the right relocations for Xqcilb
+## relative jumps. These can be resolved within the same section
+## (when relaxations are disabled) but otherwise require a
+## vendor-specific relocation pair.
 
+# This is required so that the conditional jumps are not compressed
+# by the assembler
 .option exact
 
-qc.e.j foo
-# RELOC: R_RISCV_CUSTOM195 foo 0x0
-# INSTR: qc.e.j foo
+# ASM-LABEL: this_section:
+# OBJ-LABEL: <this_section>:
+this_section:
+
+# ASM: qc.e.j undef
+# OBJ: qc.e.j 0x0 <this_section>
+# OBJ-NEXT: R_RISCV_VENDOR QUALCOMM{{$}}
+# OBJ-NEXT: R_RISCV_CUSTOM195 undef{{$}}
+qc.e.j undef
+
+# ASM: qc.e.jal undef
+# OBJ-NEXT: qc.e.jal 0x6 <this_section+0x6>
+# OBJ-NEXT: R_RISCV_VENDOR QUALCOMM{{$}}
+# OBJ-NEXT: R_RISCV_CUSTOM195 undef{{$}}
+qc.e.jal undef
+
+
+# ASM: qc.e.j same_section
+# OBJ-NEXT: qc.e.j 0x30 <same_section>
+qc.e.j same_section
+
+# ASM: qc.e.jal same_section
+# OBJ-NEXT: qc.e.jal 0x30 <same_section>
+qc.e.jal same_section
+
+# ASM: qc.e.j same_section_extern
+# OBJ-NEXT: qc.e.j 0x18 <this_section+0x18>
+# OBJ-NEXT: R_RISCV_VENDOR QUALCOMM{{$}}
+# OBJ-NEXT: R_RISCV_CUSTOM195 same_section_extern{{$}}
+qc.e.j same_section_extern
 
-qc.e.jal foo
-# RELOC: R_RISCV_CUSTOM195 foo 0x0
-# INSTR: qc.e.jal foo
+# ASM: qc.e.jal same_section_extern
+# OBJ-NEXT: qc.e.jal 0x1e <this_section+0x1e>
+# OBJ-NEXT: R_RISCV_VENDOR QUALCOMM{{$}}
+# OBJ-NEXT: R_RISCV_CUSTOM195 same_section_extern{{$}}
+qc.e.jal same_section_extern
 
-# Check that a label in a different section is handled similar to an undefined symbol
-qc.e.j .bar
-# RELOC: R_RISCV_CUSTOM195 .bar 0x0
-# INSTR: qc.e.j .bar
 
-qc.e.jal .bar
-# RELOC: R_RISCV_CUSTOM195 .bar 0x0
-# INSTR: qc.e.jal .bar
+# ASM: qc.e.j other_section
+# OBJ-NEXT: qc.e.j 0x24 <this_section+0x24>
+# OBJ-NEXT: R_RISCV_VENDOR QUALCOMM{{$}}
+# OBJ-NEXT: R_RISCV_CUSTOM195 other_section{{$}}
+qc.e.j other_section
 
-# Check that jumps to a defined symbol are handled correctly
-qc.e.j .L1
-# INSTR:qc.e.j .L1
+# ASM: qc.e.jal other_section
+# OBJ-NEXT: qc.e.jal 0x2a <this_section+0x2a>
+# OBJ-NEXT: R_RISCV_VENDOR QUALCOMM{{$}}
+# OBJ-NEXT: R_RISCV_CUSTOM195 other_section{{$}}
+qc.e.jal other_section
 
-qc.e.jal .L1
-# INSTR:qc.e.jal .L1
 
-.option noexact
+# ASM-LABEL: same_section:
+# OBJ-LABEL: <same_section>:
+same_section:
+  nop
 
-.L1:
-  ret
+# ASM-LABEL: same_section_extern:
+# OBJ-LABEL: <same_section_extern>:
+  .global same_section_extern
+same_section_extern:
+  nop
 
-.section .t2
+.section .text.other, "ax", @progbits
 
-.bar:
-  ret
+# ASM-LABEL: other_section:
+# OBJ-LABEL: <other_section>:
+other_section:
+  nop