On Tue, 22 Jun 2010 03:22:40 +1000 (EST) Bruce Evans <b...@optusnet.com.au> wrote:
> On Sun, 20 Jun 2010, Marcel Moolenaar wrote:
>
> > Log:
> > Unbreak platforms with char unsigned by default. Oddly enough, GCC
> > isn't satisfied with a simple cast to int in the check against EOF,
> > so the fix is a bit involved by actually having to go through a
> > temporary variable.
>
> Perhaps that is because gcc can see that the cast has no effect, so
> the comparison can never be true if `c' is an unsigned char (unless
> unsigned char has the same number of bits as signed int), but it
> cannot see that the conversion to the temporary variable has the same
> null effect.
>
> > Modified:
> > head/cddl/contrib/opensolaris/lib/libdtrace/common/dt_lex.l
> > ==============================================================================
> > ---
> > head/cddl/contrib/opensolaris/lib/libdtrace/common/dt_lex.l
> > Sat Jun 19 22:13:40 2010 (r209357) +++
> > head/cddl/contrib/opensolaris/lib/libdtrace/common/dt_lex.l
> > Sun Jun 20 00:34:06 2010 (r209358) @@ -67,8 +67,12 @@
> > * for all subsequent invocations, which is the effect desired.
> > */
> > #undef unput
> > -#define unput(c) \
> > - if (c != EOF) yyunput( c, yytext_ptr )
> > +#define unput(c) \
> > + do { \
> > + int _c = c; \
> > + if (_c != EOF) \
> > + yyunput(_c, yytext_ptr); \
> > + } while(0)
> > #endif
> >
> > static int id_or_type(const char *);
> >
>
> This remains broken, especially on platforms with chars unsigned. No
> one should try to unput EOF, so c should never equal EOF, but if c is
> a negative character it may equal EOF and thus
>
> On platforms with chars unsigned (except exotic ones where chars have
> the same size as ints), if c is a char then it is >= 0 and thus cannot
> equal EOF (which is < 0). Since the platform is non-exotic, (int)c
> and "int _c = c;" equal c and are this still >= 0 and thus cannot
> equal EOF. Thus the comparison with EOF has no effect, and c is
> always unput.
>
> On platforms with chars signed, some chars may equal EOF. It is an
> error to unput almost any value held in a variable of type char,
> since its value might equal EOF and thus be rejected by unput(), but
> unput() should be able to handle any character in the character set.
>
> This problem is handled by ungetc() by always converting the value to
> unsigned char. Thus the value can never equal EOF, and the character
> set is effectively represented by unsigned char's, not the plain chars
> that stdio returns in some other interfaces (but not getc()).
>
> There seems to be no reason to break the warning about this instead of
> using the same approach as stdio. This depends on yyunput() not
> having similar bugs (it must take an arg of type int and convert to
> an unsigned cgar like ungetc()):
>
> #define unput(c) yyunput((unsigned char)(c), yytext_ptr)
>
> This also fixes the missing parantheses for 'c' and some style bugs.
>
> Bruce
DTrace _does_ try to unput EOF though and apparently gets away with it
on Solaris, so while yor version is correct, it is also useless.
--
Alexander Kabaev
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