[Nasm-bugs] Re: [Nasm-devel] Nasm & binutils opcode/ bug

[anonymous c. <nas...@ya...>]

> - NASM does not add the prefixe 66H before POPF and POPA.

That's because PUSHA/POPA and PUSHF/POPF default to the current
operand size, which either depends on your output format, or the
most recent BITS assembler directive.

Use an explicit O16 or O32 prefix, if you want the non-default.

For -f elf you will get:

     1 00000000 60                          pusha
     2 00000001 6660                    o16 pusha
     3 00000003 60                      o32 pusha
     4
     5 00000004 9C                          pushf
     6 00000005 669C                    o16 pushf
     7 00000007 9C                      o32 pushf
     8
     9                                  [bits 16]
    10
    11 00000008 60                          pusha
    12 00000009 60                      o16 pusha
    13 0000000A 6660                    o32 pusha
    14
    15 0000000C 9C                          pushf
    16 0000000D 9C                      o16 pushf
    17 0000000E 669C                    o32 pushf
    18
    19                                  [bits 32]
    20
    21 00000010 60                          pusha
    22 00000011 6660                    o16 pusha
    23 00000013 60                      o32 pusha
    24
    25 00000014 9C                          pushf
    26 00000015 669C                    o16 pushf
    27 00000017 9C                      o32 pushf

Whereas for e.g. -f bin you will get:

     1 00000000 60                          pusha
     2 00000001 60                      o16 pusha
     3 00000002 6660                    o32 pusha
     4
     5 00000004 9C                          pushf
     6 00000005 9C                      o16 pushf
     7 00000006 669C                    o32 pushf
     8
     9                                  [bits 16]
    10
    11 00000008 60                          pusha
    12 00000009 60                      o16 pusha
    13 0000000A 6660                    o32 pusha
    14
    15 0000000C 9C                          pushf
    16 0000000D 9C                      o16 pushf
    17 0000000E 669C                    o32 pushf
    18
    19                                  [bits 32]
    20
    21 00000010 60                          pusha
    22 00000011 6660                    o16 pusha
    23 00000013 60                      o32 pusha
    24
    25 00000014 9C                          pushf
    26 00000015 669C                    o16 pushf
    27 00000017 9C                      o32 pushf

As you can see, for ELF the default is 32-bit, whereas for BIN it
is 16-bit. You can use [BITS] to change it, and you can use O16
and O32 to get the non-default.

Or to put it another way: don't bother with those W and D suffix
variants... just like a real x86 chip.

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