HI and LO qualifiers in MIPS assembly

HI and LO qualifiers in MIPS assembly

[Nikolaos Kavvadias]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
 
Hi there

i have a question on some alternative syntaxes of the MIPS
instructions regarding the %hi and
%lo qualifiers. The %hi is necessary when specifying addition of a
carry from the lower part
highest bit.

Sometimes gas emits what i believe is a macro-instruction, e.g. this
one is for the LUI:

lui   $reg, %hi(symbol)
e.g.
lui $10,%hi(sym)

another one is:
lw $2, %lo(v)($10)

How can I expand these expressions into "normal" instructions, as
these are defined in the MIPS32 architecture manual for programmers
(vol. 2)?
I mean how does the macro-expansion take place?

thanks in advance

Nikolaos Kavvadias
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.0 (MingW32)
Comment: Using GnuPG with Thunderbird - http://enigmail.mozdev.org
 
iD8DBQFEEaRJMPiy0tCWlz4RAtQqAJ9VIpdiYPO8CFq0hAyS5BWBXfaXhACeLleD
ghNQXICGtiASo859Yt6TM48=
=yObe
-----END PGP SIGNATURE-----

Re: HI and LO qualifiers in MIPS assembly

[Thiemo Seufer]

On Fri, Mar 10, 2006 at 06:07:37PM +0200, Nikolaos Kavvadias wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>  
> Hi there
> 
> i have a question on some alternative syntaxes of the MIPS
> instructions regarding the %hi and
> %lo qualifiers. The %hi is necessary when specifying addition of a
> carry from the lower part
> highest bit.
> 
> Sometimes gas emits what i believe is a macro-instruction, e.g. this
> one is for the LUI:

I assume you mean "gcc emits ..."

> lui   $reg, %hi(symbol)
> e.g.
> lui $10,%hi(sym)
> 
> another one is:
> lw $2, %lo(v)($10)

Those aren't macros (or, pedantically speaking, macros which just
expand to single instructions with the same mnemnonic). The %hi
and %lo tell gas/ld to encode the appropriate part of the symbol
value in the associated relocation.

> How can I expand these expressions into "normal" instructions, as
> these are defined in the MIPS32 architecture manual for programmers
> (vol. 2)?

lui and lw are MIPS32 instructions. There is also a lw macro in gas
which may expand into multiple instruction for e.g.

lw $1, sym($4)

With a percent op, you get a direct mapping to a relocation.


Thiemo