在 rocket-chip 中对 opcodes 进行定制化的过程主要是在 riscv-tools/riscv-opcodes 目录中：
.
├── encoding.h --- 基础编码工具
├── LICENSE
├── Makefile --- 编译脚本
├── opcodes --- opcodes 定义，下同
├── opcodes-custom
├── opcodes-pseudo
├── opcodes-rvc
├── opcodes-rvc-pseudo
├── parse-opcodes --- opcodes 自动化生成工具
└── README.md --- 说明文档
接下来解读下 Makefile 文件中的内容：
SHELL := /bin/sh
# 定义目标 encoding.h 目标文件位置
ISASIM_H := ../riscv-isa-sim/riscv/encoding.h
PK_H := ../riscv-pk/machine/encoding.h
FESVR_H := ../riscv-fesvr/fesvr/encoding.h
ENV_H := ../riscv-tests/env/encoding.h
OPENOCD_H := ../riscv-openocd/src/target/riscv/encoding.h
ALL_OPCODES := opcodes-pseudo opcodes opcodes-rvc opcodes-rvc-pseudo opcodes-custom
install: $(ISASIM_H) $(PK_H) $(FESVR_H) $(ENV_H) $(OPENOCD_H) inst.chisel instr-table.tex priv-instr-table.tex
# 安装所有指令码到 c 语言库，并拷贝 encoding.h 文件到目标目录
$(ISASIM_H) $(PK_H) $(FESVR_H) $(ENV_H) $(OPENOCD_H): $(ALL_OPCODES) parse-opcodes encoding.h
cp encoding.h $@
cat opcodes opcodes-rvc-pseudo opcodes-rvc opcodes-custom | ./parse-opcodes -c >> $@
# 安装所有的指令码到 Chisel 代码中，通过 parse-opcodes 脚本生成 Instructions 类
inst.chisel: $(ALL_OPCODES) parse-opcodes
cat opcodes opcodes-custom opcodes-pseudo | ./parse-opcodes -chisel > $@
# 安装所有的指令码到 Go 代码中，通过 parse-opcodes 脚本生成
inst.go: opcodes opcodes-pseudo parse-opcodes
cat opcodes opcodes-pseudo | ./parse-opcodes -go > $@
instr-table.tex: $(ALL_OPCODES) parse-opcodes
cat opcodes opcodes-pseudo | ./parse-opcodes -tex > $@
priv-instr-table.tex: $(ALL_OPCODES) parse-opcodes
cat opcodes opcodes-pseudo | ./parse-opcodes -privtex > $@
.PHONY : install
执行 make install 之后，在 riscv-fesvr/fesvr/encoding.h 文件中，存在机器码的定义过程，比如：
#ifdef DECLARE_INSN
DECLARE_INSN(beq, MATCH_BEQ, MASK_BEQ)
DECLARE_INSN(bne, MATCH_BNE, MASK_BNE)
DECLARE_INSN(blt, MATCH_BLT, MASK_BLT)
DECLARE_INSN(bge, MATCH_BGE, MASK_BGE)
DECLARE_INSN(bltu, MATCH_BLTU, MASK_BLTU)
DECLARE_INSN(bgeu, MATCH_BGEU, MASK_BGEU)
DECLARE_INSN(jalr, MATCH_JALR, MASK_JALR)
DECLARE_INSN(jal, MATCH_JAL, MASK_JAL)
DECLARE_INSN(lui, MATCH_LUI, MASK_LUI)
DECLARE_INSN(auipc, MATCH_AUIPC, MASK_AUIPC)
DECLARE_INSN(addi, MATCH_ADDI, MASK_ADDI)
DECLARE_INSN(slli, MATCH_SLLI, MASK_SLLI)
DECLARE_INSN(slti, MATCH_SLTI, MASK_SLTI)
...省略...
#endif
解析过程
简单分析下 parse-opcodes 文件中生成 encoding.h 文件部分的实现：
...此前省略...
def make_c(match,mask):
print '/* Automatically generated by parse-opcodes. */'
print '#ifndef RISCV_ENCODING_H'
print '#define RISCV_ENCODING_H'
// 递归指令名称列表，组装 MATCH_*, MASK_*, CSR_*, CAUSE_* 等宏定义
for name in namelist:
name2 = name.upper().replace('.','_')
print '#define MATCH_%s %s' % (name2, hex(match[name]))
print '#define MASK_%s %s' % (name2, hex(mask[name]))
for num, name in csrs+csrs32:
print '#define CSR_%s %s' % (name.upper(), hex(num))
for num, name in causes:
print '#define CAUSE_%s %s' % (name.upper().replace(' ', '_'), hex(num))
print '#endif'
// 定义 INSN 指令
print '#ifdef DECLARE_INSN'
for name in namelist:
name2 = name.replace('.','_')
print 'DECLARE_INSN(%s, MATCH_%s, MASK_%s)' % (name2, name2.upper(), name2.upper())
print '#endif'
// 声明 CSR
print '#ifdef DECLARE_CSR'
for num, name in csrs+csrs32:
print 'DECLARE_CSR(%s, CSR_%s)' % (name, name.upper())
print '#endif'
// 声明 CAUSE
print '#ifdef DECLARE_CAUSE'
for num, name in causes:
print 'DECLARE_CAUSE("%s", CAUSE_%s)' % (name, name.upper().replace(' ', '_'))
print '#endif'
...此后省略...
Opcodes 定义文件
以 opcodes-rvc-pseudo 文件为例，其中包含了一些特定的指令：
# these aren't really pseudo-ops, but they overlay other encodings,
# so they are here to prevent parse-opcodes from barfing
@c.nop 1..0=1 15..13=0 12=0 11..7=0 6..2=0
@c.addi16sp 1..0=1 15..13=3 12=ignore 11..7=2 6..2=ignore
@c.jr 1..0=2 15..13=4 12=0 11..7=ignore 6..2=0
@c.jalr 1..0=2 15..13=4 12=1 11..7=ignore 6..2=0
@c.ebreak 1..0=2 15..13=4 12=1 11..7=0 6..2=0
# RV64C
@c.ld 1..0=0 15..13=3 12=ignore 11..2=ignore # c.flw for RV32
@c.sd 1..0=0 15..13=7 12=ignore 11..2=ignore # c.fsw for RV32
@c.addiw 1..0=1 15..13=1 12=ignore 11..2=ignore # c.jal for RV32
@c.ldsp 1..0=2 15..13=3 12=ignore 11..2=ignore # c.flwsp for RV32
@c.sdsp 1..0=2 15..13=7 12=ignore 11..2=ignore # c.fswsp for RV32
