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Hello

I am trying to write code that includes a certain number of NOPs in the
generated machine code, I would like to do it portably so without using
inline asm.

On lccwin, even without optimisations, no NOPs are generated. I have
searched the documentation but there does not seem to be any compiler
option covering NOP generation. Can anyone help?

Here is the C code:

main()
{
;
;
;
;
;
puts("done");
}

Here is the generated assembly - as you can see, the 5 NOPs are missing.

.file "c:\\nop_test.c"
_$M0:
.file "c:\\nop_test.c"
.text
.text
; 1 main()
.type _main,function
_main:
; 2 {
.line 2
; 3 ;
; 4 ;
; 5 ;
; 6 ;
; 7 puts("done");
.line 7
pushl $_$2
call _puts
addl $4,%esp
movl $0,%eax
_$1:
; 8 }
.line 8
ret
_$3:
.size _main,_$3-_main
.globl _main
.extern _puts
.data
_$2:
; "done\x0"
.byte 100,111,110,101,0

Edward Rutherford <> writes:

> I am trying to write code that includes a certain number of NOPs in the
> generated machine code, I would like to do it portably so without using
> inline asm.

There is no portable way to do that.
--
Ben Pfaff
http://benpfaff.org

In comp.compilers.lcc Edward Rutherford <> wrote:

> I am trying to write code that includes a certain number of NOPs in the
> generated machine code, I would like to do it portably so without using
> inline asm.

> On lccwin, even without optimisations, no NOPs are generated. I have
> searched the documentation but there does not seem to be any compiler
> option covering NOP generation. Can anyone help?

The "null statement" exists in many languages as a place to put a
statement label without attaching it to a statement that does
something else. Otherwise, it is also convenient sometimes for
the grammar to allow for it for other reasons. In C, for example,
it is sometimes needed as the statement in a for or while loops.

while(something()) ;

I have never known a compiler, for any language, to generate
assembly NOP for the null statement.

> Here is the C code:

> main()
> {
> ;
> ;
> ;
> ;
> ;
> puts("done");
> }

-- glen

Le 04/01/11 23:30, Edward Rutherford a écrit :
> Hello
>
> I am trying to write code that includes a certain number of NOPs in the
> generated machine code, I would like to do it portably so without using
> inline asm.
>
> On lccwin, even without optimisations, no NOPs are generated. I have
> searched the documentation but there does not seem to be any compiler
> option covering NOP generation. Can anyone help?
>
> Here is the C code:
>
> main()
> {
> ;
> ;
> ;
> ;
> ;
> puts("done");
> }

lccwin generates NO CODE for an empty statement. I do not know where
you got the idea that an empty statement should generate a NOP

That idea is completely wrong, sorry.

BUT THERE IS SOLUTION:

I can develop a special version FOR YOU that will emit a NOP
when you write an empty statemnt.

Please write to
jacob at jacob dot remcomp dot fr

for pricing...

jacob navia <> writes:

> Le 04/01/11 23:30, Edward Rutherford a écrit :
>> I am trying to write code that includes a certain number of NOPs in the
>> generated machine code, I would like to do it portably so without using
>> inline asm.
>
> I can develop a special version FOR YOU that will emit a NOP
> when you write an empty statemnt.

A special version of lcc-win will not be a portable solution.
--
Ben Pfaff
http://benpfaff.org

Le 04/01/11 23:50, Ben Pfaff a écrit :
> jacob navia<> writes:
>
>> Le 04/01/11 23:30, Edward Rutherford a écrit :
>>> I am trying to write code that includes a certain number of NOPs in the
>>> generated machine code, I would like to do it portably so without using
>>> inline asm.
>>
>> I can develop a special version FOR YOU that will emit a NOP
>> when you write an empty statemnt.
>
> A special version of lcc-win will not be a portable solution.

Ahhh c'mon Ben, why screw my business?

Besides it is 100 portable, you can copy it in as many machines as you
like, and if you put it in a USB key, you can carry it around anywhere.

100% PORTABLE!

Ben Pfaff wrote:
> jacob navia <> writes:
>
>> Le 04/01/11 23:30, Edward Rutherford a écrit :
>>> I am trying to write code that includes a certain number of NOPs in
>>> the generated machine code, I would like to do it portably so without
>>> using inline asm.
>>
>> I can develop a special version FOR YOU that will emit a NOP when you
>> write an empty statemnt.
>
> A special version of lcc-win will not be a portable solution.

True - perhaps C needs a new nop keyword to be added.

Jacob is obviously joking about "pricing" - this would be a very easy
fix, only a few minutes work, and I would suggest having a compile time
option so that all users of lcc can choose how they want C empty
statements to be translated, in case some of them prefer the old
behaviour.

Edward Rutherford <> writes:
> I am trying to write code that includes a certain number of NOPs in the
> generated machine code, I would like to do it portably so without using
> inline asm.
>
> On lccwin, even without optimisations, no NOPs are generated. I have
> searched the documentation but there does not seem to be any compiler
> option covering NOP generation. Can anyone help?
>
> Here is the C code:
>
> main()
> {
> ;
> ;
> ;
> ;
> ;
> puts("done");
> }
>
> Here is the generated assembly - as you can see, the 5 NOPs are missing.
[snip]

An empty statement does not specify the generation of any particular
machine instruction.

In fact, *no* C statement specifies the generation of any particular
machine instruction. The job of a compiler is to generate code
that implements the semantics of your C program, not to generate
any particular CPU instructions. (C has been called a "portable
assembler", but it really isn't.)

If you want to generate a particular number of NOP instructions
(I won't ask why), you'll have to use some implementation-specific
method. I think lcc-win supports some sort of non-standard inline
asm; you said you don't want to use inline asm, but that's pretty
much your best option. No portable C solution exists.

Followups redirected.

--
Keith Thompson (The_Other_Keith) kst- <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

Le 04/01/11 23:54, Edward Rutherford a écrit :
> Ben Pfaff wrote:
>> jacob navia<> writes:
>>
>>> Le 04/01/11 23:30, Edward Rutherford a écrit :
>>>> I am trying to write code that includes a certain number of NOPs in
>>>> the generated machine code, I would like to do it portably so without
>>>> using inline asm.
>>>
>>> I can develop a special version FOR YOU that will emit a NOP when you
>>> write an empty statemnt.
>>
>> A special version of lcc-win will not be a portable solution.
>
> True - perhaps C needs a new nop keyword to be added.
>

#define __nop__ _asm("nop")

I can't understand why inline asm is not used here...

On Jan 4, 4:54*pm, Edward Rutherford
<edward.p.rutherfor...@REMOVETHIS.gmail.com> wrote:
> Ben Pfaff wrote:
> > jacob navia <ja...@spamsink.net> writes:
>
> >> Le 04/01/11 23:30, Edward Rutherford a écrit :
> >>> I am trying to write code that includes a certain number of NOPs in
> >>> the generated machine code, I would like to do it portably so without
> >>> using inline asm.
>
> >> I can develop a special version FOR YOU that will emit a NOP when you
> >> write an empty statemnt.
>
> > A special version of lcc-win will not be a portable solution.
>
> True - perhaps C needs a new nop keyword to be added.
>
> Jacob is obviously joking about "pricing" - this would be a very easy
> fix, only a few minutes work, and I would suggest having a compile time
> option so that all users of lcc can choose how they want C empty
> statements to be translated, in case some of them prefer the old
> behaviour.


Perhaps a __nop intrinsic (which, somewhat bizarrely, has been
implemented on a fair number of compilers), would be a better idea.
(Tongue-sort-of-in-cheek)