Date: Tue, 13 Mar 2007 16:34:00 +0300 From: Eygene Ryabinkin <rea-fbsd@codelabs.ru> To: Max Laier <max@love2party.net> Cc: freebsd-current@freebsd.org Subject: Re: Bad gcc -O optimization cause core dump. What to do? Message-ID: <20070313133400.GW58523@codelabs.ru> In-Reply-To: <200703131415.45709.max@love2party.net> References: <20070313121106.GA96293@nagual.pp.ru> <20070313123717.GU58523@codelabs.ru> <200703131415.45709.max@love2party.net>
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Slightly off-topic, sorry. > > > Any ideas? Is it right or needs to be fixed? > > > > It is definitely not right, since it produces the bad code. > > And there are no compilation-time checks that can say for > > sure will the argument for the "%s" be NULL: > > This is simply a programming error. Just because the function is called > printf doesn't make it right. It's nice that the libc's printf does all > these neat tricks, but it's also expensive (See the link I posted > earlier). According to the printf(3) manpage: > > s The char * argument is expected to be a pointer to an array of > character type (pointer to a string). Characters from the array > are written up to (but not including) a terminating NUL charac- > ter; if a precision is specified, no more than the number speci- > fied are written. If a precision is given, no null character > need be present; if the precision is not specified, or is greater > than the size of the array, the array must contain a terminating > NUL character. > > And I fail to see how "NULL" is a valid pointer to an array of character > type. This is C after all. In linux there were times (in 2.6 kernel) when mmap was able to return NULL as the handle to a perfectly valid memory area. So NULL is sometimes a good pointer. But it is not our case, so this was off-topic, just for the curiosity. I just wanted to point out that the familiar behaviour of printf() can be restored with the -fno-builtin-printf flag. -- Eygene
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