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Tue, 9 Mar 2021 21:29:59 +0000 Date: Tue, 9 Mar 2021 21:29:57 +0000 (UTC) From: shwaresyst To: eblake@redhat.com, bruno@clisp.org, cbouchar@redhat.com, bug-m4@gnu.org, libc-alpha@sourceware.org, austin-group-l@opengroup.org Message-ID: <1569476484.1894162.1615325397167@mail.yahoo.com> Subject: Re: SIGSTKSZ is now a run-time variable MIME-Version: 1.0 References: <1569476484.1894162.1615325397167.ref@mail.yahoo.com> X-Mailer: WebService/1.1.17872 aolandroid Mozilla/5.0 (Linux; Android 10; LM-G850 Build/QKQ1.200216.002; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/89.0.4389.86 Mobile Safari/537.36 AolApp/5.15.0.2962 X-Spam-Status: No, score=1.1 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, HTML_MESSAGE, KAM_GOODAOL, RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H2, SPF_HELO_NONE, SPF_PASS, TXREP, XM_RANDOM autolearn=no autolearn_force=no version=3.4.2 X-Spam-Level: * X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Content-Filtered-By: Mailman/MimeDel 2.1.29 X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 09 Mar 2021 21:30:02 -0000 Yes, it's not something an application would expect to need to keep increas= ing, just that's the part of I'd move it to. The definition coul= d also be the max required by a processor family, with sysconf() reporting = a possible lower value for a particular processor stepping. At least that w= ay the application that doesn't use sysconf() won't be getting SIGSEGV faul= ts. Additionally, I believe the definition can be calculated at compile time as= a multiple of ( sizeof(ucontext_t)+sizeof(overhead_struct(s)) ), whatever = other overhead applies, so I don't see any real need to use sysconf(). This= may mean having to munge a by configure, based on config.guess= , but that's not the standard's headache. The CS, SC, and PC constants are not in the XSH 2.2.2 table deliberately, f= rom Issue 6 TC1, as adding any also requires a bump in POSIX_VERSION or POS= IX2_VERSION, and often XSI_VERSION. This is so each usage of a constant doe= sn't need individual #ifdefs to test option group availability. The previou= s text was allowing if an implementation wasn't supporting an option group = they could skip including the related constants in . A simple che= ck of VERSION at the top of a source C file suffices now to indicate those = constants shall be available. On Tuesday, March 9, 2021 Eric Blake wrote: On 3/9/21 10:14 AM, shwaresyst wrote: >=20 > To me that looks like a conformance violation and should be reverted. The= re is no _SC_SIGSTKSZ defined in 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.=C2=A0 Then again, re-reading X= SH 2.2.2: " Implementations may add symbols to the headers shown in the following table, provided the identifiers for those symbols either: =C2=A0 =C2=A0 Begin with the corresponding reserved prefixes in the table, = or ..." but the table lacks a row for with _CS_* and _SC_* constants. Looks like you found an independent defect. >=20 > I could see the definition of SIGSTKSZ being changed to the static minimu= m a particular processor requires, or is initially allocated as a 'safe' am= ount, rather than static "default size", and moving SIGSTKSZ to .= This would contrast to MINSIGSTKSZ as the lowest value for a platform for = all supported processors. Then an application could use sysconf() to query = for the maximum size the configuration supports if it wants to use more tha= n that, as a runtime increasable limit. As I understand it, the concern in glibc is less about runtime increasability, so much as ABI compatibility with applications compiled against older headers at a time when the kernel had less state information to store during a context switch. --=20 Eric Blake, Principal Software Engineer Red Hat, Inc.=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 +1-919-301-3226 Virtualization:=C2=A0 qemu.org | libvirt.org