From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by sourceware.org (Postfix) with ESMTPS id 2B4C93858D39 for ; Wed, 19 Oct 2022 12:23:54 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 2B4C93858D39 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1666182233; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:mime-version:mime-version: content-type:content-type:in-reply-to:in-reply-to: references:references; bh=hnra4DvlfCZl42ZFkwMr0MV4Jdf9xb0Zn1n0xn1dETw=; b=iQgekqAhN1TBWyTA9NOoMHDwfrZL2nUw0aJKYeM7K8+xkYd2ae0HEo4L8LIVdUhDQZz0wU YUWe9Skd/yCZkDnaWSf/s536ecNwH1xyfiltsZL5DdFn/CuGc4qJNX8GbN96NMQg+z3G71 5jX9wjbCH691BEP1GdRZDNToHJHyC5Y= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-615-sShgtOqVO2y_B_BswCGmog-1; Wed, 19 Oct 2022 08:23:50 -0400 X-MC-Unique: sShgtOqVO2y_B_BswCGmog-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 5CA7081D9EB; Wed, 19 Oct 2022 12:23:50 +0000 (UTC) Received: from tucnak.zalov.cz (unknown [10.39.193.252]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 170CD4081B60; Wed, 19 Oct 2022 12:23:49 +0000 (UTC) Received: from tucnak.zalov.cz (localhost [127.0.0.1]) by tucnak.zalov.cz (8.17.1/8.17.1) with ESMTPS id 29JCNkGe3957474 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NOT); Wed, 19 Oct 2022 14:23:47 +0200 Received: (from jakub@localhost) by tucnak.zalov.cz (8.17.1/8.17.1/Submit) id 29JCNk7q3957473; Wed, 19 Oct 2022 14:23:46 +0200 Date: Wed, 19 Oct 2022 14:23:45 +0200 From: Jakub Jelinek To: Lewis Hyatt via Gcc-patches , Lewis Hyatt , richard.sandiford@arm.com Subject: Re: [PATCH] pch: Fix streaming of strings with embedded null bytes Message-ID: Reply-To: Jakub Jelinek References: MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Spam-Status: No, score=-3.7 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE,TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On Wed, Oct 19, 2022 at 01:17:02PM +0100, Richard Sandiford wrote: > Jakub Jelinek writes: > > On Wed, Oct 19, 2022 at 12:54:11PM +0100, Richard Sandiford via Gcc-patches wrote: > >> Lewis Hyatt via Gcc-patches writes: > >> > When a GTY'ed struct is streamed to PCH, any plain char* pointers it contains > >> > (whether they live in GC-controlled memory or not) will be marked for PCH > >> > output by the routine gt_pch_note_object in ggc-common.cc. This routine > >> > special-cases plain char* strings, and in particular it uses strlen() to get > >> > their length. Thus it does not handle strings with embedded null bytes, but it > >> > is possible for something PCH cares about (such as a string literal token in a > >> > macro definition) to contain such embedded nulls. To fix that up, add a new > >> > GTY option "string_length" so that gt_pch_note_object can be informed the > >> > actual length it ought to use, and use it in the relevant libcpp structs > >> > (cpp_string and ht_identifier) accordingly. > >> > >> This isn't really my area, as I'm about to demonstrate with this > >> question, but: regarding > >> > >> if (note_ptr_fn == gt_pch_p_S) > >> (*slot)->size = strlen ((const char *)obj) + 1; > >> else > >> (*slot)->size = ggc_get_size (obj); > >> > >> do you know why the PCH code goes out of its way to handle the sizes of > >> strings specially? Are there enough garbage strings in the string pool > >> that it's worth optimising the size of the saved memory for strings but > >> not for other types of object? Or is the gt_pch_p_S test needed for > >> correctness, rather than just being an optimisation? > > > > Just guessing, not all GC strings live in the stringpool. > > Isn't e.g. ggc_strdup just a GC allocation where the string length > > isn't stored anywhere? > > Is that different from other GC VLA allocations though? I thought > ultimately we just tried to save and restore the containing pages. I think just the objects in it, not entire pages (ggc_get_size (obj) sized chunks for non-strings). > > And sometimes it isn't even GC allocated, e.g. ggc_strdup ("") just > > returns ""; I guess const char * pointers in GC memory can also point > > to string literals in .rodata and for PCH we move them. > > Ah, OK, that would definitely explain it, thanks. In that case, > are you OK with the patch, as a way of continuing to support rodata > string pointers while also allowing embedded nuls? LGTM. Jakub