Re: Assembler in Ada?

[dewar@gnat.com]

In article <78a32f$dbr$1@remarQ.com>,
>     Asm (
>              "movl  %1,    %%eax"  & nl &    -- note nl

This is a bad idea, use one Asm call per instruction.
Also you probably do NOT want to use an explicit register
here. It is allowed, but it usually at the wrong level.
It is true one does this more on the ia32 than other
machines, but it is poor as an example.

You do not need to set the clobbers argument in this case
to %%eax, it won't cause trouble to do so, but there is no
need, and in an example it is confusing.

>           False  -- compiler, do not optimise my code

It is quite wrong to mark this as volatile, this is not
a volatile instruction.


> From the last example you can see that it is necessary to
> be very careful when
> manually controlling passing varaibles to the registers.

It is generally a bad idea to write asm code at this level
(a level where you rely on detailed knowledge of the ABI
for passing parameters), and it is not necessary.

Once again, we recommend that anyone interested in using
this feature read the documentation in the GCC manual. The
design of the ASM feature in Ada has been chosen to be a
very thin binding to the corresponding C feature, so that
documentation and examples apply without any confusion.

Robert Dewar
Ada Core Technologies


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