From: Roland Illig <roland.illig@gmx.de>
Date: Fri, 01 Jul 2022 18:58:25 GMT
Subject: Re: undefined behavior in builtin/am.c
Message-ID: <647f50a7-4350-fe04-fb84-b79417d98455@gmx.de>
In-Reply-To: <Yr80s8VP8ECCXKd+@coredump.intra.peff.net>

Am 01.07.2022 um 19:53 schrieb Jeff King:
> On Fri, Jul 01, 2022 at 07:03:18PM +0200, Roland Illig wrote:
>
>> The macro 'isspace' must only be called with an integer representable as
>> an 'unsigned char', or with the value of the macro EOF.
>>
>> On platforms where plain 'char' is a signed integer type, any character
>> whose value is negative invokes undefined behavior (except for the one
>> character that by coincidence has the same value as the macro EOF).
>>
>> To fix this, write '!isspace((unsigned char)*str)' instead.
>>
>> I have no idea how to trigger this part of the code but for someone who
>> knows this part of Git, it should be easy. Depending on the platform,
>> this kind of error may be silently ignored or crash the program, as
>> always with undefined behavior.
>
> We don't use the system isspace(), but instead our own macro wrappers in
> git-compat-util.h. They do the cast to unsigned char themselves.

Thanks for the explanation, good to know that there's no problem. :)

Roland