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Date: Wed, 23 Nov 2022 14:16:31 +0100
From: Alejandro Colomar <>
To: Stefan Puiu <>, Guillem Jover <>,
 Andrew Clayton <>,,
 Michael Kerrisk <>, Alejandro Colomar
 <>, Brian Inglis <>,
 Rich Felker <>,
Subject: Re: [PATCH] memmem.3: Added list of known systems where this is

Hi all!

On 11/23/22 13:52, Stefan Puiu wrote:
> Hi,
> On Wed, Nov 23, 2022 at 1:39 AM Guillem Jover <> wrote:
>> Hi!
>> On Thu, 2022-11-10 at 12:36:47 +0100, Alejandro Colomar wrote:
>>> On 11/10/22 01:13, Andrew Clayton wrote:
>>>> While looking at which systems provide memmem(3) I have been able to
>>>> discern the following:
>>>>     musl libc since v0.9.7
>>>>     bionic since Android 9
>>>>     FreeBSD since 6.0
>>>>     OpenBSD since 5.4
>>>>     NetBSD
>>>>     macOS
>>>>     Illumos
>>>> For macOS and Illumos I checked the memmem(3) man page on those systems.
>>>> For the rest there are links below to on-line man pages or commit logs.
>>>> +FreeBSD 6.0, OpenBSD 5.4, NetBSD, macOS & Illumos.
>>> For the commit message, it's interesting to note macOS and Bionic, for
>>> speleology purposes.  However, I'm opposed to adding them to the page itself
>>> because of the following:
>>> -  macOS is not free software.  I refuse to reference nonfree software on
>>> this project.
>> I understand where you are coming from,


>> and from a full system PoV,
>> it's very true that macOS is non-free. But the lower layers of its
>> stack are free software (at least according to the FSF and OSI), such
>> as its kernel (Darwin), or its libc (where memmem() is implemented):
>> among others.

Hmmm.  Fair enough.

>> Similar with Solaris and Illumos (but with the CDDL, MIT, BSD), AFAIUI.
>>> -  Android is not a real Unix system, in that you can't even program in C in
>>> there, unless you're Google or have hacked your system.  It's not friendly
>>> to us programmers, so we don't need to be friendly to it.  I don't want to
>>> be cluttering the pages with information that is irrelevant to normal users.
>> I'm assuming bionic is being used in some of the Android free
>> alternatives too, but then I'm not sure how usable for programming those
>> are either. And, well musl libc is not a real Unix system you can program
>> against either. :)

The difference is only that bionic is not in use in useful systems (AFAIK).  :)

So we have to do some decission here (and also about newlib, as reported by Brian).

>> In any case I also find it useful to have this kind of portability
>> information when deciding what to use in code.

And I must admit it's also useful to me (this all started because Andrew and I 
had to use memmem(3) at a project where macOS compatibility is relevant --not 
critical, but relevant--).

>> But can understand the
>> reluctance to include such references, at least if thought out as the
>> entire system. Perhaps thinking about these merely at their kernel or
>> libc level would make including information about some of them more
>> palatable, given that standalone they are free software? So perhaps
>> an option is to instead refer to their specific components, say
>> "bionic libc X.Y", "Apple Libc M.N.O" or similar.

Yep, that's more palatable :)

I think I'd accept a patch stating Apple Libc version for memmem(3).

> Not sure if it's the job of Linux man-pages to document when other
> OSes started supporting certain APIs. That info has to be maintained,
> updated etc. People can always read the man pages of other systems,
> right? Maybe it's worth only pointing out when an interface is
> Linux-only, or the Linux implementation diverges significantly.

The good thing is that in most cases, it's either something in POSIX (for which 
I gon't care at all if Apple Libc or another-weirdo-libc decide to not support 
it), or it's a Linux-only function.

So, there are few functions or syscalls that are generally available but are not 
in POSIX, and it might be interesting to document that they're effectively as 
portable as anything POSIX.  Maybe even POSIX editors read this and decide to 
add it.

In those cases, we still need to decide what we care about or not.

Musl libc is definitely a first-class citizen these days in Linux distributions. 
  I would start documenting them in the project at large if someone from musl 
provides patches (I discussed this some time ago, but can't remember with who).
Rich, if you would like to discuss about this, we can have some chat.

> For musl and other libcs, I think the man pages already document some
> instances where their behavior diverges from glibc.

As said, for musl, I'd document them officially, if there's anyone interested 
enough to send patches.

For other libcs, we have to decide if they're important enough, and probably 
decide on a case-by-case basis.

Michael tried to have some decent coverage of non-GNU/Linux systems, both in the 
man-pages and in his TLPI book.  It's a useful thing.  So much that sometimes 
you don't even need to read other systems' pages at all to know how portable is 
a GNU/Linux function.

So, I'd like to get opinions on interest about documenting details about:

- newlib (I never heard about it before; is it a widespread thing? do you think 
it's useful?)
- Apple Libc (I still don't like it, but I must admit that it's relevant, and 
being open source, it's more palatable)
- bionic (does anyone know if that's useful at all for anyone at all?)

Support for those wouldn't go as far as musl or glibc.  For now it would only be 
for memmem(3).




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