ghidra python script for fixing "Unknown Error" in the decompile window of RISC-V binary ( for RV64I language binary )

fix_riscv_decompile.py

# Check out the issue for more detail : https://github.com/NationalSecurityAgency/ghidra/issues/2466  
# The script will calculate the value of gp register base on the code in entry(), then apply the value to all the functions
# This only work in the `RV64I` language though, since other language like `RV64GC` won't set the gp register in entry()

from java.math import BigInteger

def newAddress(offset):
    """
    Helper function to get a Ghidra Address type
    """
    return currentProgram.getAddressFactory().getDefaultAddressSpace().getAddress(offset)

# get entry() function code unit
listing = currentProgram.getListing()
entry_func = getGlobalFunctions("entry")[0] # one entry function, just get it from index
addrSet = entry_func.getBody() # get the body address range
codeUnits = listing.getCodeUnits(addrSet, True) # get code units ( instructions and their addresses...). true means 'forward'

gp = None

def cal_gp():
    """
    Calculate the value of gp ( global pointer register )
    """
    global codeUnits, gp
    if gp != None:
        return
    gp = 0    
    for codeUnit in codeUnits:
        # print codeUnit info
        # from binascii import hexlify
        # print("0x{} : {:16} {}".format(codeUnit.getAddress(), hexlify(codeUnit.getBytes()), codeUnit.toString()))
        asm = codeUnit.toString()
        # gp = (<auipc's imm> << 12) + <pc_of_auipc> + <addi's imm>
        if "auipc gp" in asm:
            imm = int(asm.split(",")[-1], 16)
            gp = (imm << 12) + codeUnit.getAddress().getOffset() # getOffset so it returns a integer
        elif "addi gp,gp" in asm:
            imm = int(asm.split(",")[-1], 16)
            gp += imm
            return

cal_gp() # calculate gp
print("gp value: {:#x}".format(gp))

# Get all functions
# Modify all the gp register in those functions ( except "entry()" )
gp_reg = currentProgram.getRegister("gp") # get Register type of gp
fm = currentProgram.getFunctionManager()
funcs = fm.getFunctions(True) # True means 'forward'
for func in funcs: 
    if(func.getName() == "entry"): # skip entry()
        continue
    
    print("===================================")
    print("Function: {} @ 0x{}".format(func.getName(), func.getEntryPoint()))
    addrSet = func.getBody()
    addrStart = addrSet.getMinAddress()
    addrEnd = addrSet.getMaxAddress()
    print("Address start: 0x{}".format(addrStart))
    print("Address end: 0x{}".format(addrEnd))
    print("Modify the value of gp register...")
    currentProgram.programContext.setValue(gp_reg, addrStart, addrEnd, BigInteger.valueOf(gp))
    print("OK !")
    print("===================================")
    
print("All done !")