Asm style

Asm style

[vda]

I'm using GCC 3.0.1 and seeing "multi-line literals are deprecated".
Since a patch is necessary for that (and someone submitted it already)
I'd like to hear from big kernel guys what asm statement style to use:
	asm(
"		cmd	r,r\n"
"lbl:		cmd	r,r\n"
"		cmd	r,r\n"
		: spec
		: spec
	);
[variable width for labels? I don't like it] or
	asm(
	"	cmd	r,r\n"
	"lbl:	cmd	r,r\n"
	"	cmd	r,r\n"
		: spec
		: spec
	);
[better. But \n's are ugly] or
#define NL "\n"
	asm(
	"	cmd	r,r" NL
	"lbl:	cmd	r,r" NL
	"	cmd	r,r" NL
		: spec
		: spec
	);
[I like this: \n doesn't interfere with args]
or what?
--
vda

Re: Asm style

[Ben Collins]

On Wed, Nov 21, 2001 at 11:07:03PM +0000, vda wrote:
> I'm using GCC 3.0.1 and seeing "multi-line literals are deprecated".
> Since a patch is necessary for that (and someone submitted it already)
> I'd like to hear from big kernel guys what asm statement style to use:
> 	asm(
> "		cmd	r,r\n"
> "lbl:		cmd	r,r\n"
> "		cmd	r,r\n"
> 		: spec
> 		: spec
> 	);
> [variable width for labels? I don't like it] or
> 	asm(
> 	"	cmd	r,r\n"
> 	"lbl:	cmd	r,r\n"
> 	"	cmd	r,r\n"
> 		: spec
> 		: spec
> 	);
> [better. But \n's are ugly] or
> #define NL "\n"
> 	asm(
> 	"	cmd	r,r" NL
> 	"lbl:	cmd	r,r" NL
> 	"	cmd	r,r" NL
> 		: spec
> 		: spec
> 	);

There's also:

	asm("\
	cmd	r,r\n\
lbl:	cmd	r,r\n\
	cmd	r,r\n" : spec : spec);


Or something similar (the trailing "\" added for continuation). Probably
the easiest way to patch existing asm.

-- 
 .----------=======-=-======-=========-----------=====------------=-=-----.
/                   Ben Collins    --    Debian GNU/Linux                  \
`  bcollins@debian.org  --  bcollins@openldap.org  --  bcollins@linux.com  '
 `---=========------=======-------------=-=-----=-===-======-------=--=---'

Re: Asm style

[Giacomo Catenazzi]

ncw@axis.demon.co.uk wrote:
> Giacomo Catenazzi wrote:
>> 
>> not ANSI C. The trailing \ is understood only in marco definitions
>> (and outside strings)
>> 
> gcc begs to differ
> 
> /* z.c */
> #include <stdio.h>
> 
> int main(void)
> {
>     printf("This is a string\n\
> with continuation characters\n");
>     return 0;
> }
> 
> $ gcc -Wall -pedantic -ansi z.c -o z
> [silence]
> 
> Remove the \ and you get
> 
> z.c:5: warning: string constant runs past end of line
> z.c: In function `main':
> z.c:5: warning: ANSI C forbids newline in string constant
> 

gcc should warn in both case (when calling it with -pedantic -ansi).
But forget my comment:
Talking about ANSI C for asm construct doen't make much sense.

If gcc people will maintain (in long future) the syntax of
trailing \ + NL, I agree to use it into kernel.

	giacomo

Re: Asm style

[Jakub Jelinek]

On Thu, Nov 22, 2001 at 03:29:07PM +0100, Giacomo Catenazzi wrote:
> gcc should warn in both case (when calling it with -pedantic -ansi).
> But forget my comment:
> Talking about ANSI C for asm construct doen't make much sense.

It should not warn.
Please read ISO C99 5.1.1.2:
2.  Each instance of a backslash character (\) immediately followed by a new-line
    character is deleted, splicing physical source lines to form logical source lines.
    Only the last backslash on any physical source line shall be eligible for being part
    of such a splice. A source file that is not empty shall end in a new-line character,
    which shall not be immediately preceded by a backslash character before any such
    splicing takes place.
This happens even before tokenizing (and before macro expansion too).

	Jakub

Re: Asm style

[Giacomo Catenazzi]

Ben Collins wrote:
> 
> There's also:
> 
> 	asm("\
> 	cmd	r,r\n\
> lbl:	cmd	r,r\n\
> 	cmd	r,r\n" : spec : spec);
> 
> 
> Or something similar (the trailing "\" added for continuation). Probably
> the easiest way to patch existing asm.
> 

not ANSI C. The trailing \ is understood only in marco definitions
(and outside strings)

	giacomo

Re: Asm style

[ncw]

Giacomo Catenazzi wrote:
>  Ben Collins wrote:
> > There's also:
> > 
> > 	asm("\
> > 	cmd	r,r\n\
> > lbl:	cmd	r,r\n\
> > 	cmd	r,r\n" : spec : spec);
> > 
> > 
> > Or something similar (the trailing "\" added for continuation). Probably
> > the easiest way to patch existing asm.
>  
>  not ANSI C. The trailing \ is understood only in marco definitions
>  (and outside strings)

gcc begs to differ

/* z.c */
#include <stdio.h>

int main(void)
{
    printf("This is a string\n\
with continuation characters\n");
    return 0;
}

$ gcc -Wall -pedantic -ansi z.c -o z
[silence]

Remove the \ and you get

z.c:5: warning: string constant runs past end of line
z.c: In function `main':
z.c:5: warning: ANSI C forbids newline in string constant

You are correct in thinking it is something to do with pre-processor -
it deals with these continuation lines eg,

$ gcc -E -Wall -pedantic -ansi z.c

Gives
[snip stdio etc]
int main(void)
{
    printf("This is a string\nwith continuation characters\n");

    return 0;
}

-- 
Nick Craig-Wood
ncw@axis.demon.co.uk

Re: Asm style

[Andi Kleen]

vda <vda@port.imtp.ilyichevsk.odessa.ua> writes:

> I'm using GCC 3.0.1 and seeing "multi-line literals are deprecated".
> Since a patch is necessary for that (and someone submitted it already)

The best patch for this IMHO would be to just remove the stupid warning
from gcc. It's obvious that whoever added it has never used gcc inline
assembly.

If they want to remove multi-line strings they need to supply a way to
write inline assembly without strings first. Both solutions below
are very error prone and ugly.

Failing that:

> 	asm(
> 	"	cmd	r,r\n"
> 	"lbl:	cmd	r,r\n"
> 	"	cmd	r,r\n"

Is bearable with some pains.


> #define NL "\n"
> 	asm(
> 	"	cmd	r,r" NL
> 	"lbl:	cmd	r,r" NL

Is also bearable, but needs agreement (needs a central #define) 

-Andi