[{"id":3673214,"web_url":"http://patchwork.ozlabs.org/comment/3673214/","msgid":"<4d3feac6-ece3-4846-bcb3-9265ff308999@oss.qualcomm.com>","list_archive_url":null,"date":"2026-04-03T16:33:20","subject":"Re: [PATCH] strlen: Fix up memcpy/strcpy/strcat handling [PR124754]","submitter":{"id":92310,"url":"http://patchwork.ozlabs.org/api/people/92310/","name":"Jeffrey Law","email":"jeffrey.law@oss.qualcomm.com"},"content":"On 4/3/2026 2:48 AM, Jakub Jelinek wrote:\n> Hi!\n>\n> The following testcase ICEs because it tries to use a freed strinfo.\n> strinfo uses refcounting and vectors of pointers to those are either shared\n> in between bbs or unshared when some later bb needs to modify something.\n>\n> The ICE is due to the second memcpy handling. Since r10-5451 it first\n> calls get_stridx on dst (&a), then get_strinfo with the returned index and\n> then get_stridx on src (&a + 24). &a has been referenced earlier and\n> the pass knows some details on its string length (let's ignore that the\n> testcase invokes UB for now, I think it can happen even on valid code,\n> just haven't managed to adjust the testcase, but supposedly the unreduced\n> original is valid), so the strinfo is shared with other bbs.\n> WHen get_stridx is called for &a + 24, it sees it doesn't know anything\n> about that yet and wants to create a strinfo for it. But related strinfos\n> are chained, so &a's next should be &a + 24 in this testcase, that means\n> we need to unshare the &a strinfo so that we can modify it while keeping\n> the one entry used by earlier bbs unmodified. The problem is that\n> handle_builtin_memcpy called get_strinfo before this, so it got hands on\n> the old still not unshared strinfo for &a and because it isn't refreshed\n> after the get_stridx call by another get_strinfo call, we try to unshare\n> it again and break the refcounting.\n>\n> So, basically for calls which call get_stridx twice, we need top make sure\n> we do both get_stridx calls before the first get_strinfo call, or repeat\n> get_strinfo after the second get_stridx call.\n>\n> In handle_builtin_memcpy it used to be right and got broken by r10-5451,\n> but I'm in strcpy/strcat handling I've screwed it up since the pass was\n> added.\n>\n> Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux,\n> ok for trunk and eventually backports?\n>\n> 2026-04-03 Jakub Jelinek \n>\n> \tPR tree-optimization/124754\n> \t* tree-ssa-strlen.cc (strlen_pass::handle_builtin_strcpy): Make\n> \tsure both get_stridx calls are done before first get_strinfo call.\n> \t(strlen_pass::handle_builtin_memcpy): Likewise.\n> \t(strlen_pass::handle_builtin_strcat): Likewise.\n>\n> \t* g++.dg/tree-ssa/strlenopt-3.C: New test.\nOK.\njeff","headers":{"Return-Path":"","X-Original-To":["incoming@patchwork.ozlabs.org","gcc-patches@gcc.gnu.org"],"Delivered-To":["patchwork-incoming@legolas.ozlabs.org","gcc-patches@gcc.gnu.org"],"Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=qualcomm.com header.i=@qualcomm.com header.a=rsa-sha256\n header.s=qcppdkim1 header.b=XoWnRpIp;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=oss.qualcomm.com header.i=@oss.qualcomm.com\n header.a=rsa-sha256 header.s=google header.b=BvyZWVBm;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org\n (client-ip=2620:52:6:3111::32; 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