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assemblyx86-64nasmmasm

equivalent MASM .const section in NASM

What is the exact NASM equivalent of below MASM code?

; Simple lookup table (.const section data is read-only)
      .const
const_array dword 0, 1, 1, 2, 3, 5, 8, 13, 21
Solution

  • Because the .const MASM directive denotes a read-only segment, you have to use the NASM equivalent section .rdata1 which creates a segment/section which is readable, but not writeable.

    You can put DWORDs anywhere by using the DD directive; see Section 3.2.1 of the manual.

    The final result could look like this:

    section .rdata
  const_array:   dd 0, 1, 1, 2, 3, 5, 8, 13, 21

    A : after label names is always recommended in NASM.

    When the first token on the line isn't recognized as an instruction mnemonic NASM will assume it's a label. But it's a good habit to always use : to make that unambiguous.

    Footnote 1:

    Windows uses .rdata. Some other OSes including Linux use section .rodata for read-only non-executable data.