Fail to assemble mov al, -1

[ghost]

#include <Zydis/Zydis.h>
#include <Zycore/LibC.h>

int main()
{
    ZyanU8 encoded_instruction[ZYDIS_MAX_INSTRUCTION_LENGTH];
    ZyanUSize encoded_length = sizeof(encoded_instruction);
    ZydisEncoderRequest req;
    ZYAN_MEMSET(&req, 0, sizeof(req));
    req.mnemonic = ZYDIS_MNEMONIC_MOV;
    req.machine_mode = ZYDIS_MACHINE_MODE_LONG_64;
    req.operand_count = 2;
    req.operands[0].type = ZYDIS_OPERAND_TYPE_REGISTER;
    req.operands[0].reg.value = ZYDIS_REGISTER_AL;
    req.operands[1].type = ZYDIS_OPERAND_TYPE_IMMEDIATE;
    req.operands[1].imm.s = -1;
    if (ZYAN_FAILED(ZydisEncoderEncodeInstruction(&req, encoded_instruction, &encoded_length)))
    {
        ZYAN_PUTS("Failed to encode instruction");
        return 1;
    }
    for (ZyanUSize i = 0; i < encoded_length; ++i)
    {
        ZYAN_PRINTF("%02X ", encoded_instruction[i]);
    }
    ZYAN_PUTS("");
    return 0;
}

Should assemble, but fails. It works if req.operands[1].imm.u = 0xFF; instead.

[mappzor]

That's because all gpr8, imm have immediate value marked as unsigned. I mentioned that problem in #192. Some months ago we agreed to change several instruction definitions like this one (where signedness doesn't really exist) to "signed by default". This change will improve consistency with other definitions and automatically fix such encoding problems. I've started this effort but never finished it. It's a tedious process and it can be automated only partially. I still intend to fix it one day. For now your workaround is the intended way of handling this.