[RISCV] Support Parsing Nonstandard Relocations (#119909)

This allows nonstandard relocation names to be used in `.reloc` assembly
directives (giving the correct relocation number).

No translation is done by the assembler into `R_RISCV_CUSTOM<n>` names,
and the assembler does not automatically add the relevant
`R_RISCV_VENDOR` relocation with the vendor symbol. If we want, we can
have a different directive that does this later.

The first batch of relocations to be added are from [Qualcomm's RISC-V
psABI
extensions](https://github.com/quic/riscv-elf-psabi-quic-extensions/releases/tag/v0.1).

Author: lenary

llvm/include/llvm/BinaryFormat/ELF.h

@@ -689,6 +689,9 @@ enum : unsigned {
 // ELF Relocation types for RISC-V
 enum {
 #include "ELFRelocs/RISCV.def"
+#define ELF_RISCV_NONSTANDARD_RELOC(_vendor, name, value) name = value,
+#include "ELFRelocs/RISCV_nonstandard.def"
+#undef ELF_RISCV_NONSTANDARD_RELOC
 };
 
 enum {

llvm/include/llvm/BinaryFormat/ELFRelocs/RISCV_nonstandard.def

@@ -0,0 +1,28 @@
+//===--- RISC-V Nonstandard Relocation List ---------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef ELF_RISCV_NONSTANDARD_RELOC
+#error "ELF_RISCV_NONSTANDARD_RELOC must be defined"
+#endif
+
+// ELF_RISCV_NONSTANDARD_RELOC(VENDOR, NAME, ID) defines information about
+// nonstandard relocation codes. This can be used when parsing relocations, or
+// when printing them, to provide better information.
+//
+// VENDOR should be the symbol name expected in the associated `R_RISCV_VENDOR`
+// relocation. NAME and ID work like `ELF_RELOC` but the mapping is not expected
+// to be 1:1.
+//
+// The mapping in RISCV.def is 1:1, and should be used when the only information
+// available is the relocation enum value.
+
+// Qualcomm Nonstandard Relocations
+ELF_RISCV_NONSTANDARD_RELOC(QUALCOMM, R_RISCV_QC_ABS20_U,    192)
+ELF_RISCV_NONSTANDARD_RELOC(QUALCOMM, R_RISCV_QC_E_BRANCH,   193)
+ELF_RISCV_NONSTANDARD_RELOC(QUALCOMM, R_RISCV_QC_E_32,       194)
+ELF_RISCV_NONSTANDARD_RELOC(QUALCOMM, R_RISCV_QC_E_JUMP_PLT, 195)

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

@@ -38,9 +38,12 @@ std::optional<MCFixupKind> RISCVAsmBackend::getFixupKind(StringRef Name) const {
   if (STI.getTargetTriple().isOSBinFormatELF()) {
     unsigned Type;
     Type = llvm::StringSwitch<unsigned>(Name)
-#define ELF_RELOC(X, Y) .Case(#X, Y)
+#define ELF_RELOC(NAME, ID) .Case(#NAME, ID)
 #include "llvm/BinaryFormat/ELFRelocs/RISCV.def"
 #undef ELF_RELOC
+#define ELF_RISCV_NONSTANDARD_RELOC(_VENDOR, NAME, ID) .Case(#NAME, ID)
+#include "llvm/BinaryFormat/ELFRelocs/RISCV_nonstandard.def"
+#undef ELF_RISCV_NONSTANDARD_RELOC
                .Case("BFD_RELOC_NONE", ELF::R_RISCV_NONE)
                .Case("BFD_RELOC_32", ELF::R_RISCV_32)
                .Case("BFD_RELOC_64", ELF::R_RISCV_64)

llvm/test/MC/RISCV/custom_reloc.s

@@ -21,16 +21,33 @@
   .reloc ., R_RISCV_VENDOR,    VENDOR_NAME
   .reloc ., R_RISCV_CUSTOM192, my_foo + 1
   addi a0, a0, 0
-  # CHECK-ASM: [[L1:.L[^:]+]]:
+  # CHECK-ASM:      [[L1:.L[^:]+]]:
   # CHECK-ASM-NEXT: .reloc [[L1]], R_RISCV_VENDOR, VENDOR_NAME
   # CHECK-ASM-NEXT: [[L2:.L[^:]+]]:
   # CHECK-ASM-NEXT: .reloc [[L2]], R_RISCV_CUSTOM192, my_foo+1
   # CHECK-ASM-NEXT: mv a0, a0
 
-  # CHECK-OBJ: addi a0, a0, 0
+  # CHECK-OBJ:      addi a0, a0, 0
   # CHECK-OBJ-NEXT: R_RISCV_VENDOR    VENDOR_NAME
   # CHECK-OBJ-NEXT: R_RISCV_CUSTOM192 my_foo+0x1
 
   nop
   # CHECK-ASM: nop
   # CHECK-OBJ: addi zero, zero, 0x0
+
+  .reloc ., R_RISCV_VENDOR,     QUALCOMM
+  .reloc ., R_RISCV_QC_ABS20_U, my_bar + 2
+  addi a1, a1, 0
+  # CHECK-ASM:      [[L3:.L[^:]+]]:
+  # CHECK-ASM-NEXT: .reloc [[L3]], R_RISCV_VENDOR, QUALCOMM
+  # CHECK-ASM-NEXT: [[L4:.L[^:]+]]:
+  # CHECK-ASM-NEXT: .reloc [[L4]], R_RISCV_QC_ABS20_U, my_bar+2
+  # CHECK-ASM-NEXT: mv a1, a1
+
+  # CHECK-OBJ:      addi a1, a1, 0
+  # CHECK-OBJ-NEXT: R_RISCV_VENDOR    QUALCOMM
+  # CHECK-OBJ-NEXT: R_RISCV_CUSTOM192 my_bar+0x2
+
+  nop
+  # CHECK-ASM: nop
+  # CHECK-OBJ: addi zero, zero, 0x0