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Re: SIGSTKSZ is now a run-time variable

From: Eric Blake
Subject: Re: SIGSTKSZ is now a run-time variable
Date: Tue, 9 Mar 2021 14:12:35 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0

On 3/9/21 1:34 PM, Eric Blake via austin-group-l at The Open Group wrote:
> On 3/9/21 10:14 AM, shwaresyst wrote:
>> To me that looks like a conformance violation and should be reverted. There 
>> is no _SC_SIGSTKSZ defined in <unistd.h> by the standard, to begin with, so 
>> that use of sysconf() is a non-portable extension on its own.
> Portable apps can't use _SC_SIGSTKSZ, but the standard generally permits
> implementations to define further constants.  Then again, re-reading XSH
> 2.2.2:
> " Implementations may add symbols to the headers shown in the following
> table, provided the identifiers for those symbols either:
>     Begin with the corresponding reserved prefixes in the table, or
> ..."
> but the table lacks a row for <unistd.h> with _CS_* and _SC_* constants.
>  Looks like you found an independent defect.

Not quite, because later it states "The following identifiers are
reserved regardless of the inclusion of headers: 1. With the exception
of identifiers beginning with the prefix _POSIX_, all identifiers that
begin with an <underscore> and either an uppercase letter or another
<underscore> are always reserved for any use by the implementation.", so
an implementation can blindly add _SC_* constants at will without
violating the standard.

Still, I opened:
to try and add some clarification.

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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