On Tue, Apr 10, 2007 at 09:05:55AM -0700, Andrew Morton wrote:
> On Tue, 10 Apr 2007 07:23:35 -0400 (EDT) "Robert P. J. Day" <[email protected]> wrote:
> > Following the programming advice laid down in the gcc manual, make
> > sure the case "..." operator has spaces on either side.
> > http://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/Case-Ranges.html#Case-Ranges:
> >
> > "Be careful: Write spaces around the ..., for otherwise it may be
> > parsed wrong when you use it with integer values."
> > --- a/kernel/audit.c
> > +++ b/kernel/audit.c
> > @@ -515,8 +515,8 @@ static int audit_netlink_ok(struct sk_buff *skb, u16 msg_type)
> > err = -EPERM;
> > break;
> > case AUDIT_USER:
> > - case AUDIT_FIRST_USER_MSG...AUDIT_LAST_USER_MSG:
> > - case AUDIT_FIRST_USER_MSG2...AUDIT_LAST_USER_MSG2:
> > + case AUDIT_FIRST_USER_MSG ... AUDIT_LAST_USER_MSG:
> > + case AUDIT_FIRST_USER_MSG2 ... AUDIT_LAST_USER_MSG2:
>
> hm... We have:
>
> #define AUDIT_FIRST_USER_MSG 1100 /* Userspace messages mostly uninteresting to kernel */
> #define AUDIT_USER_AVC 1107 /* We filter this differently */
> #define AUDIT_LAST_USER_MSG 1199
>
> and CPP turns that into
>
> case 1100 ...1199:
> case 2100 ...2999:
>
> and it does the same when the comments are stripped from the #defines.
>
> So we were saved by the trailing space which cpp added to the expanded
> macro. I wonder why cpp did that, and to what extent one can rely cpp
> doing that.
The only reason I can come up with is temporary files with preprocessing
output. Imagine the code:
#define FOO 1
FOO.
Here we have
a) replacement list of token FOO consists of one token -- 1,
b) pp-token list after preprocessing consists of 4 pp-tokens: newline, 1, .,
newline
BUT, write it to temporary file:
1.
Whoops, there are 3 or 4 pp-tokens? If you don't know history, there are
3, if you do, there are 4.
-
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