musl - Re: Re: realloci(): A realloc() variant that works in-place

Follow @Openwall on Twitter for new release announcements and other news

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <zxqlvsofala2hrm3gmu7tr5nwe3njalt7f6bviz5gdhc2kcp6o@6oo2jlyl3hfv>
Date: Mon, 10 Nov 2025 11:07:29 +0100
From: Alejandro Colomar <alx@...nel.org>
To: Paul Eggert <eggert@...ucla.edu>
Cc: Rich Felker <dalias@...c.org>, libc-alpha@...rceware.org, 
	musl@...ts.openwall.com, "A. Wilcox" <AWilcox@...cox-tech.com>, 
	Lénárd Szolnoki <cpp@...ardszolnoki.com>, Collin Funk <collin.funk1@...il.com>, 
	Arthur O'Dwyer <arthur.j.odwyer@...il.com>, Jonathan Wakely <jwakely@...hat.com>, 
	"Paul E. McKenney" <paulmck@...nel.org>, Thiago Macieira <thiago@...ieira.org>
Subject: Re: Re: realloci(): A realloc() variant that works in-place

Hi Paul, Rich,

On Sun, Nov 09, 2025 at 06:47:54PM -0800, Paul Eggert wrote:
> On 2025-11-09 17:20, Rich Felker wrote:
> > The only way the lifetime of P does not end is if realloc returns a
> > null pointer indicating failure.
> 
> Yes, and my point was that Alejandro's summary of the situation (which you
> went along with) got this detail wrong. And once one gets this detail right
> (which static analyzers of course can do), that discredits the idea that
> static analyzers are so dumb that they can't handle conditional results from
> functions like realloc. On the contrary, static analyzers do that sort of
> thing routinely, and they could continue to do so if the standard were
> changed slightly in the direction I proposed.

I agree I was wrong in my wording.  And considering that
[[gnu::malloc(free)]] doesn't imply [[gnu::malloc]], then your proposed
semantics are also easy to express.  I guess this could do it:

	void *eggert_realloc(void *, size_t);
	[[gnu::malloc(eggert_realloc, 1)]] [[gnu::malloc(free)]]
	void *eggert_realloc(void *, size_t);

	void *current_realloc(void *, size_t);
	[[gnu::malloc(current_realloc, 1)]] [[gnu::malloc(free)]]
	[[gnu::malloc]]
	void *current_realloc(void *, size_t);

And since analyzers already need to consider when it fails, I guess
you're right that adding p==q to the logic of the analyzer wouldn't hurt
so much.


Have a lovely day!
Alex

-- 
<https://www.alejandro-colomar.es>
Use port 80 (that is, <...:80/>).

Download attachment "signature.asc" of type "application/pgp-signature" (834 bytes)

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.