[Nasm-bugs] [Bug 3392782] New: Support for rex.w

[noreply-nasm at dev.nasm.us]

https://bugzilla.nasm.us/show_bug.cgi?id=3392782

            Bug ID: 3392782
           Summary: Support for rex.w
           Product: NASM
           Version: 2.14.xx
          Hardware: PC
                OS: Linux
            Status: OPEN
          Severity: normal
          Priority: Medium
         Component: Assembler
          Assignee: nobody at nasm.us
          Reporter: mackan.dubois at gmail.com
                CC: chang.seok.bae at intel.com, gorcunov at gmail.com,
                    hpa at zytor.com, nasm-bugs at nasm.us
     Obtained from: From OS distribution

Hi,

I'm trying to assemble the following statement on Ubuntu 20.04

rex.w retf

I expect this to generate the following bytes 0x48 0xcb. But the
assembler only outputs 0xcb. I've tried using rex64 instead of rex.w
but the result is the same. 64-bits mode i nasm assumed.

Assembling the above instruction on GNU AS works fine.

My current workaround is to manually input the 0x48 byte inline as follows

db 0x48
retf

But that seems like a hack. Is this a bug or am I missing something?


Best regards,

Marcus

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