Newer gcc swallow version control keywords

[Nadav Har'El]

On Mon, Oct 17, 2011, Oleg Goldshmidt wrote about "Re: Newer gcc swallow version control keywords":
> > In any case, because there was always a fear that the compiler might
> > optimize these out, someone invented a new directive, #ident, as in:
> >
> > #ident "$Id$"
> 
> This has always been there, but it has never been standard, AFAIK. It

"Always" is always a relative term, when we're talking about a programming
language (C) invented 40 years ago. I'm pretty sure #ident has indeed been
around for around 20 years. About standardization, you may be right: I just
checked and sadly I can't find "#ident" anywhere in the C99 standard.

But that being said, I wonder if in practice, on actual computers of interest
today, it will work. I just checked on my Fedora 15, Gcc 4.6.1, and it works
well. Sadly, all the dozen other Unix variants to which I used to have access,
have gone the way of the dodo, so I can't check this on any other C compiler.

> is not a GCC extension, either. Most preprocessors don't barf on
> directives they do not understand, but they may simply ignore #ident
> which will lead to the same behaviour that I do not want.

They *may* ignore #ident, but like I said, #ident has been around for ages,
and may actually work on many if not all compilers. Like I said, it does
on gcc. I checked, and it seems it  generates assemly that looks like:

        .ident  "$Id: hello $"

Which I guess GNU AS supports, seeing that the ident string appears in the
object file and in the final executable - even if compiled with -O2.


> When you say that it has worked for you with all sorts of compilers do
> you mean that it actually produced the $Id$ string with ident or that
> it didn't break? 

Whenever I checked, it worked in the sense of generating code.
But I was never a big fan of what(1) and ident(1) like you, so I haven't
checked this in ages.

> I was wondering whether someone would catch my little mischief: this
> bug report complains about the same effect in a slightly different
> situation. Even with older GCC the $Id$ string is not there with just
> -O2, but it is with "-g -O2" (cf. my original posting - I put the
> exact command line there for a reason). 
> 
> Yes, I agree with the opinion that -fkeep-static-consts should
> override optimization (it is more specific), but it has never been the
> case (or at least not for a very long time).

I suggest you add your comments to that bug report, to make it known that
people still care. Apparently, you're the last user (!?) of ident(1), so
make your voice heard :-)

-- 
Nadav Har'El                        |                   Tuesday, Oct 18 2011, 
nyh at math.technion.ac.il             |-----------------------------------------
Phone +972-523-790466, ICQ 13349191 |Unix is user friendly - it's just picky
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