Date: Tue, 15 Jan 2013 08:46:34 -0500 From: Rich Felker <dalias@...ifal.cx> To: musl@...ts.openwall.com Subject: Re: malloc(0) behaviour On Tue, Jan 15, 2013 at 12:06:18PM +0100, Szabolcs Nagy wrote: > * Igmar Palsenberg <igmar@...senberg.com> [2013-01-15 09:31:24 +0100]: > > > fundamental reasons too. Basically they all come down to interactions > > > between the requirements of malloc and realloc, and the fact that > > > returning a null pointer from realloc means failure (and thus that the > > > > > > http://www.open-std.org/jtc1/sc22/wg14/www/docs/dr_400.htm > > > http://austingroupbugs.net/view.php?id=400 > > > http://sourceware.org/bugzilla/show_bug.cgi?id=12547 > > > > While the above is clear to me, returning a pointer that can't hold anything just seems wrong to me. > > i don't think we have too many options here, > the standards and historical practices has > various inconsistencies and musl has the least > broken one > > but we can do a theoretical discussion about > the merits of malloc(0)!=0: > > i'm surprised that it "seems wrong" to you, > you can access the amount of bytes you requested > through the returned pointer p, evaluating > p+size is valid, p is suitably aligned for all > objects and it can be freed. > these assumptions are broken if malloc(0)==0 > > if the standard made malloc(0) work in ansi c > then it would save some branch logic and would > made the world a safer place > (because in a fair amount of code that gets > array length from external source no special > casing would be needed for length==0) In fairness, there's hardly any difference between the work involved in: if (size < LIMIT) and if (size-1 < LIMIT-1) The latter catches 0 and treats it as invalid. > > I'll wrap malloc() to include an abort in my case :) > > but don't do that in library code that may be > used in a long running process: allocation failures > should be reported to let the caller handle it I think he meant malloc(0) would abort to indicate that, in the rules of his project, malloc(0) is a programming error. This is not such a bad idea.. Rich
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