From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from paperclip.tbsaunde.org (tbsaunde.org [66.228.47.254]) by sourceware.org (Postfix) with ESMTP id 61A9E3851C0D for ; Fri, 2 Jul 2021 00:44:20 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 61A9E3851C0D Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=tbsaunde.org Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=tbsaunde.org Received: from rag (pool-108-24-42-131.cmdnnj.fios.verizon.net [108.24.42.131]) by paperclip.tbsaunde.org (Postfix) with ESMTPSA id BA204C0DB; Fri, 2 Jul 2021 00:44:19 +0000 (UTC) Date: Thu, 1 Jul 2021 20:44:17 -0400 From: Trevor Saunders To: David Malcolm Cc: Richard Biener , GCC Patches Subject: Re: [PATCH 2/4] allow poisoning input_location in ranges it should not be used Message-ID: References: <20210630053529.26581-1-tbsaunde@tbsaunde.org> <20210630053529.26581-2-tbsaunde@tbsaunde.org> <907daf69d72fedce3dd9ee8a9dccc59d7d22a08a.camel@redhat.com> <1d9c0179fa3e19f9056ac65fd05964866315e2c5.camel@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1d9c0179fa3e19f9056ac65fd05964866315e2c5.camel@redhat.com> X-Spam-Status: No, score=-11.9 required=5.0 tests=BAYES_00, GIT_PATCH_0, KAM_DMARC_STATUS, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 02 Jul 2021 00:44:21 -0000 On Thu, Jul 01, 2021 at 11:40:55AM -0400, David Malcolm via Gcc-patches wrote: > On Thu, 2021-07-01 at 14:53 +0200, Richard Biener wrote: > > On Thu, Jul 1, 2021 at 12:16 PM Trevor Saunders < > > tbsaunde@tbsaunde.org> wrote: > > > > > > On Wed, Jun 30, 2021 at 11:13:23AM -0400, David Malcolm wrote: > > > > On Wed, 2021-06-30 at 01:35 -0400, Trevor Saunders wrote: > > > > > This makes it possible to assert if input_location is used > > > > > during the > > > > > lifetime > > > > > of a scope.  This will allow us to find places that currently > > > > > use it > > > > > within a > > > > > function and its callees, or prevent adding uses within the > > > > > lifetime > > > > > of a > > > > > function after all existing uses are removed. > > > > > > > > > > bootstrapped and regtested on x86_64-linux-gnu, ok? > > > > > > > > > > Trev > > > > > > > > [...snip...] > > > > > > > > > diff --git a/gcc/diagnostic.c b/gcc/diagnostic.c > > > > > index d58586f2526..3f68d1d79eb 100644 > > > > > --- a/gcc/diagnostic.c > > > > > +++ b/gcc/diagnostic.c > > > > > @@ -1835,7 +1835,7 @@ internal_error (const char *gmsgid, ...) > > > > >    auto_diagnostic_group d; > > > > >    va_list ap; > > > > >    va_start (ap, gmsgid); > > > > > -  rich_location richloc (line_table, input_location); > > > > > +  rich_location richloc (line_table, UNKNOWN_LOCATION); > > > > >    diagnostic_impl (&richloc, NULL, -1, gmsgid, &ap, DK_ICE); > > > > >    va_end (ap); > > > > > > > > > > > > > I actually make use of this in the analyzer: the analyzer sets > > > > input_location to stmt->location when analyzing a given stmt - > > > > that > > > > way, if the analyzer ICEs, the ICE is shown at the code construct > > > > that > > > > crashed the analyzer. > > > > > > > > This behavior is useful to me, and would be lost with the > > > > proposed > > > > patch. > > > > > > I made this change because otherwise if the compiler ICE's while > > > access > > > to input_location is blocked we end up infinitely recursing > > > complaining > > > we can't access it while trying to say where the last error was.  I > > > was > > > nervous about the change before, and now I agree we need something > > > else. > > > > > > > Is there a better way of doing what I'm doing? > > > > > > > > Is the long-term goal of the patch kit to reduce our reliance on > > > > global > > > > variables?  Are we ultimately still going to need a variable for > > > > "where > > > > to show the ICE if gcc crashes"?  (perhaps stashing it in the > > > > diagnostic_context???) > > > > > > Yes, the goal is ultimately removal of global state, however I'm > > > not > > > really ure what the better approach to your problem is, after all > > > even > > > moving it to the diagnostic context is sort of a global state, and > > > sort > > > of dupplicates input_location.  That said it is somewhat more > > > constrained, so if it removes usage of input_location perhaps its > > > worthwhile? > > > > Reduction of global state is of course good - but in particular > > input_location > > should be something only used during parsing because it's a quite > > broken concept otherwise.  And fiddling with it tends to be quite > > fragile... > > for example see g:7d6f7e92c3b737736a2d8ff97a71af9f230c2f88 > > for the "fun" you can have with "stale" values in input_location ... > > Yeah. Another example, from the analyzer, is > g:2fbea4190e76a59c4880727cf84706fe083c00ae (PR 93349) So, one rather useful this patch allows doing, even if you apply it locally, is that you can block off access to input_location in the same scope you currently save and restore it, and then once you've fixed up all the asserts you find with a bootstrap and test cycle, you can be somewhat confident nothing uses it and the save and restore dance can go. I may have a look at doing that with some of these. > > > IMHO users should have their own "copy", for example the gimplifier > > instead of mucking with and using input_location could use a > > similar state in its gimplify_ctx. > > Some ideas (not necessarily good ones): > > (a) the diagnostic_context could have an ice_location field, and use > that in internal_error (and maybe an RAII class for setting/clearing > it). If this is useful to people as it seems to be, this seems sensible, my one concern is when exactly should ice_location be set? other than "it should match input_location". There's still the global state of the diagnostic context, but at least its more understandable and isolated. On the other hand it offers the opertunity to have a stack of ice_locations, if you walk up the stack looking at all the RAII objects, perhaps that would be useful, especially with things like template instantiation? > (b) move input_location to diagnostic_context, and add: > #define input_location (global_dc->x_input_location) > or: > #define input_location (global_dc->x_default_location) > which add an indirection everywhere. I don't love these ideas, in that > we already overuse the preprocessor IMHO. There's that, also it doesn't seem to really reduce the complexity? it just merges too globals into one block of memory? Thanks Trev > > Trevor: BTW, if you're looking for global state to eliminate, it might > be nice to move the globals in input.c for caching source lines > (fcache_tab etc) into a new source_cache class, and have the > diagnostic_context own it via a new "source_cache *" field. > > Dave >