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Date: Wed, 3 Jan 2024 09:11:24 +0900
To: cygwin AT cygwin DOT com
Cc: Kaz Kylheku <kaz AT kylheku DOT com>
Subject: Re: Possibly buggy use of ctype.h macros.
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From: Takashi Yano via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>
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On Tue, 02 Jan 2024 15:56:00 -0800
Kaz Kylheku <kaz AT kylheku DOT com> wrote:

> On 2024-01-02 15:25, Takashi Yano via Cygwin wrote:
> > On Tue, 02 Jan 2024 14:18:15 -0800
> > Kaz Kylheku via Cygwin <cygwin AT cygwin DOT com> wrote:
> >> I noticed that this macro, defined in winsup/cygwin/local_includes/path.h:
> >>
> >>   #define isdrive(s) (isalpha (*(s)) && (s)[1] == ':')
> >>
> >> is being used with arguments of type char, like dereferenced "char *" pointers.
> >>
> >> Unless the isalpha implementation is robust against this, it should be isalpha((unsigned char) *(s)).
> > 
> > 
> > https://cygwin.com/git/?p=newlib-cygwin.git;a=blob;f=newlib/libc/ctype/ctype_.h;h=a73870b3e4ade5545fd41bcc6f10446a22b4b46e;hb=HEAD
> 
> I see, so on Cygwin, the negative index is allowed, thanks to a displacement.
> 
> # define DEFAULT_CTYPE_PTR      ((char *) _ctype_b + 127)
> 
> But, 127? A (signed) char can go to -128. '\x80' will access _ctype_b[-1]. Is that also somehow OK?
> 
> (Tangential remark: all ctype implementations have to handle at least one negative value, namely EOF.)

https://cygwin.com/git/?p=newlib-cygwin.git;a=blob;f=newlib/libc/ctype/isalpha.c;h=8b8e78a296359a4a8b3687fd76b1b73cd707a6da;hb=HEAD

Perhaps, the off-by-one is for EOF as you guess.

-- 
Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>

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