Interesting discovery in the C library that Cygwin uses

[Matthias Andree]

Am 09.07.2010, 01:34 Uhr, schrieb Gregg Levine:

(warnings about char subscripts)

> Basically the program supporter there wants the people here for Cygwin
> to, ah, fix their C library. I'm not convinced that's necessary, but
> which C library is used here? And what could be fixed?

The C library (newlib) is fine, it is actually helpful here by emitting  
warnings for actual program defects.

The supporter should be sold a clue, in the form of a copy of IEEE  
Standard 1003.1 or a deep link to the opengroup.org website.

The urjtag source however should be fixed. It abuses the ctype.h  
interfaces. Arguments to the tolower() and other to*() and isspace() and  
other is*() functions MUST be cast to unsigned char (unless they are  
already unsigned char). Background is that these functions need to support  
the usual 8bit character range plus the 257th "character" EOF (-1).  So  
the is*() functions will have to use a wider type than char, and now sign  
extension matters. If you don't cast the input to unsigned char, an  
argument of 0xff will alias EOF although it is not the same, and  
0x80...0xfe will lead to undefined behaviour, possibly even crashes.

Note: the warning may be specific to Cygwin, but the underlying program  
will show on more systems with input outside ASCII.  I recall that at  
least some versions of Solaris would misbehave if you passed non-ASCII  
characters (think umlauts or accented characters, or Asian/Cyrillic/other  
national scripts) to these ctype.h functions.  There are probably more...

-- 
Matthias Andree

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