From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.223.130]) by sourceware.org (Postfix) with ESMTPS id F14113858D37 for ; Thu, 18 Apr 2024 07:41:21 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org F14113858D37 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=suse.de Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=suse.de ARC-Filter: OpenARC Filter v1.0.0 sourceware.org F14113858D37 Authentication-Results: server2.sourceware.org; arc=none smtp.remote-ip=195.135.223.130 ARC-Seal: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1713426084; cv=none; b=wBJIi1qkGNLdZWAE1kvo9V2Rfy2Tj0c9mtzrwuxZ+sBh/u6aIyFyekywoSle5jIyn/bpiwd9YEvumBBAnlH3fi7UV47wuiSPO79dUiigVlof9Ew4X9CCGZvupXC/GvJgk1oXAkiPoOGtt2oDhIRjPUXHABXGj7EpMK7wzcU1pq4= ARC-Message-Signature: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1713426084; c=relaxed/simple; bh=YSoFZzmCC52VvozScOdveNs4J1dbikzNHZZf5+Aw3Pg=; h=DKIM-Signature:DKIM-Signature:DKIM-Signature:DKIM-Signature:Date: From:To:Subject:Message-ID:MIME-Version; b=YoLPGIsdDtJOKAmuDYQo2JGXoJ5952m1Ldz+j+6f1/t2HLeiOUfhObh/vYpOCOidj/9uMaWZYYf30OuVZn/gEIS+s6Y8nks/w3ZGZ19WOBk5WYb6eCXHckROvleOlWOosbylN4hOq95yDJ46krFvbnxBrRFyLMIS9b7EXfnspDc= ARC-Authentication-Results: i=1; server2.sourceware.org Received: from [10.168.5.241] (unknown [10.168.5.241]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id 060B234B05; Thu, 18 Apr 2024 07:41:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1713426081; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=v5aMsCQHF+YOlvWZpYW+XL+wrf5YVmY3Uh5iXSr/lUc=; b=JQf2vQVmBntwOGPZQKZaerWc5s3ZpO8VvA1qFrUnvi37MTl+tXtjpq7SMzlxQSWqFMl2tH Nu7mTUYp2T+vnhGE95JsUrBTmS4k5VaVh/s2Kuk9p4hI0a3TF6/TXnHKOBAAUcYxBnavJ7 tIjJfYnT7u1OnwmYMd9f00/5riWE7do= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1713426081; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=v5aMsCQHF+YOlvWZpYW+XL+wrf5YVmY3Uh5iXSr/lUc=; b=oq6toCSMsbJmoXeZHkhL/8MjjUHutsmwNOPBhJxFWT1T5trY12OvSbRIE21L6BnYqb3jJt Q2JdYl7F40dyyyCA== Authentication-Results: smtp-out1.suse.de; none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1713426081; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=v5aMsCQHF+YOlvWZpYW+XL+wrf5YVmY3Uh5iXSr/lUc=; b=JQf2vQVmBntwOGPZQKZaerWc5s3ZpO8VvA1qFrUnvi37MTl+tXtjpq7SMzlxQSWqFMl2tH Nu7mTUYp2T+vnhGE95JsUrBTmS4k5VaVh/s2Kuk9p4hI0a3TF6/TXnHKOBAAUcYxBnavJ7 tIjJfYnT7u1OnwmYMd9f00/5riWE7do= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1713426081; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=v5aMsCQHF+YOlvWZpYW+XL+wrf5YVmY3Uh5iXSr/lUc=; b=oq6toCSMsbJmoXeZHkhL/8MjjUHutsmwNOPBhJxFWT1T5trY12OvSbRIE21L6BnYqb3jJt Q2JdYl7F40dyyyCA== Date: Thu, 18 Apr 2024 09:41:20 +0200 (CEST) From: Richard Biener To: Jakub Jelinek cc: "Joseph S. Myers" , gcc-patches@gcc.gnu.org Subject: Re: [PATCH] libgcc: Fix up __divmodbitint4 [PR114755] In-Reply-To: Message-ID: <30p764qp-qo61-5s58-os8n-5p2874r94031@fhfr.qr> References: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Spam-Level: X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-0.990]; MIME_GOOD(-0.10)[text/plain]; MISSING_XM_UA(0.00)[]; MIME_TRACE(0.00)[0:+]; TO_DN_SOME(0.00)[]; ARC_NA(0.00)[]; RCVD_COUNT_ZERO(0.00)[0]; FROM_HAS_DN(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; RCPT_COUNT_THREE(0.00)[3]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FUZZY_BLOCKED(0.00)[rspamd.com]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:email] X-Spam-Score: -4.30 X-Spam-Status: No, score=-4.9 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,SPF_HELO_NONE,SPF_PASS,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 Thu, 18 Apr 2024, Jakub Jelinek wrote: > Hi! > > The following testcase aborts on aarch64-linux but does not on x86_64-linux. > In both cases there is UB in the __divmodbitint4 implemenetation. > When the divisor is negative with most significant limb (even when partial) > all ones, has at least 2 limbs and the second most significant limb has the > most significant bit clear, when this number is negated, it will have 0 > in the most significant limb. > Already in the PR114397 r14-9592 fix I was dealing with such divisors, but > thought the problem is only if because of that un < vn doesn't imply the > quotient is 0 and remainder u. > But as this testcase shows, the problem is with such divisors always. > What happens is that we use __builtin_clz* on the most significant limb, > and assume it will not be 0 because that is UB for the builtins. > Normally the most significant limb of the divisor shouldn't be 0, as > guaranteed by the bitint_reduce_prec e.g. for the positive numbers, unless > the divisor is just 0 (but for vn == 1 we have special cases). > > The following patch moves the handling of this corner case a few lines > earlier before the un < vn check, because adjusting the vn later is harder. > > Bootstrapped/regtested on x86_64-linux and i686-linux, plus tested with > make check-gcc -j32 -k GCC_TEST_RUN_EXPENSIVE=1 RUNTESTFLAGS="GCC_TEST_RUN_EXPENSIVE=1 dg.exp='*bitint* pr112673.c builtin-stdc-bit-*.c pr112566-2.c pr112511.c' dg-torture.exp=*bitint* dfp.exp=*bitint*" > on aarch64-linux, ok for trunk? OK. Thanks, Richard. > 2024-04-18 Jakub Jelinek > > PR libgcc/114755 > * libgcc2.c (__divmodbitint4): Perform the decrement on negative > v with most significant limb all ones and the second least > significant limb with most significant bit clear always, regardless of > un < vn. > > * gcc.dg/torture/bitint-69.c: New test. > > --- libgcc/libgcc2.c.jj 2024-03-21 13:07:43.629886730 +0100 > +++ libgcc/libgcc2.c 2024-04-17 19:00:55.453691368 +0200 > @@ -1705,69 +1705,62 @@ __divmodbitint4 (UBILtype *q, SItype qpr > USItype rn = ((USItype) rprec + W_TYPE_SIZE - 1) / W_TYPE_SIZE; > USItype up = auprec % W_TYPE_SIZE; > USItype vp = avprec % W_TYPE_SIZE; > + /* If vprec < 0 and the top limb of v is all ones and the second most > + significant limb has most significant bit clear, then just decrease > + vn/avprec/vp, because after negation otherwise v2 would have most > + significant limb clear. */ > + if (vprec < 0 > + && ((v[BITINT_END (0, vn - 1)] | (vp ? ((UWtype) -1 << vp) : 0)) > + == (UWtype) -1) > + && vn > 1 > + && (Wtype) v[BITINT_END (1, vn - 2)] >= 0) > + { > + vp = 0; > + --vn; > +#if __LIBGCC_BITINT_ORDER__ == __ORDER_BIG_ENDIAN__ > + ++v; > +#endif > + } > if (__builtin_expect (un < vn, 0)) > { > - /* If abs(v) > abs(u), then q is 0 and r is u. > - Unfortunately un < vn doesn't always mean abs(v) > abs(u). > - If uprec > 0 and vprec < 0 and vn == un + 1, if the > - top limb of v is all ones and the second most significant > - limb has most significant bit clear, then just decrease > - vn/avprec/vp and continue, after negation both numbers > - will have the same number of limbs. */ > - if (un + 1 == vn > - && uprec >= 0 > - && vprec < 0 > - && ((v[BITINT_END (0, vn - 1)] | (vp ? ((UWtype) -1 << vp) : 0)) > - == (UWtype) -1) > - && (Wtype) v[BITINT_END (1, vn - 2)] >= 0) > - { > - vp = 0; > - --vn; > + /* q is 0 and r is u. */ > + if (q) > + __builtin_memset (q, 0, qn * sizeof (UWtype)); > + if (r == NULL) > + return; > #if __LIBGCC_BITINT_ORDER__ == __ORDER_BIG_ENDIAN__ > - ++v; > + r += rn - 1; > + u += un - 1; > #endif > + if (up) > + --un; > + if (rn < un) > + un = rn; > + for (rn -= un; un; --un) > + { > + *r = *u; > + r += BITINT_INC; > + u += BITINT_INC; > } > - else > + if (!rn) > + return; > + if (up) > { > - /* q is 0 and r is u. */ > - if (q) > - __builtin_memset (q, 0, qn * sizeof (UWtype)); > - if (r == NULL) > + if (uprec > 0) > + *r = *u & (((UWtype) 1 << up) - 1); > + else > + *r = *u | ((UWtype) -1 << up); > + r += BITINT_INC; > + if (!--rn) > return; > -#if __LIBGCC_BITINT_ORDER__ == __ORDER_BIG_ENDIAN__ > - r += rn - 1; > - u += un - 1; > -#endif > - if (up) > - --un; > - if (rn < un) > - un = rn; > - for (rn -= un; un; --un) > - { > - *r = *u; > - r += BITINT_INC; > - u += BITINT_INC; > - } > - if (!rn) > - return; > - if (up) > - { > - if (uprec > 0) > - *r = *u & (((UWtype) 1 << up) - 1); > - else > - *r = *u | ((UWtype) -1 << up); > - r += BITINT_INC; > - if (!--rn) > - return; > - } > - UWtype c = uprec < 0 ? (UWtype) -1 : (UWtype) 0; > - for (; rn; --rn) > - { > - *r = c; > - r += BITINT_INC; > - } > - return; > } > + UWtype c = uprec < 0 ? (UWtype) -1 : (UWtype) 0; > + for (; rn; --rn) > + { > + *r = c; > + r += BITINT_INC; > + } > + return; > } > USItype qn2 = un - vn + 1; > if (qn >= qn2) > --- gcc/testsuite/gcc.dg/torture/bitint-69.c.jj 2024-04-17 19:09:34.165521448 +0200 > +++ gcc/testsuite/gcc.dg/torture/bitint-69.c 2024-04-17 19:10:25.343814139 +0200 > @@ -0,0 +1,26 @@ > +/* PR libgcc/114755 */ > +/* { dg-do run { target bitint } } */ > +/* { dg-options "-std=c23" } */ > +/* { dg-skip-if "" { ! run_expensive_tests } { "*" } { "-O0" "-O2" } } */ > +/* { dg-skip-if "" { ! run_expensive_tests } { "-flto" } { "" } } */ > + > +#if __BITINT_MAXWIDTH__ >= 255 > +_BitInt(65) > +foo (void) > +{ > + _BitInt(255) a = 0x040404040404040404040404wb; > + _BitInt(65) b = -0xffffffffffffffffwb; > + _BitInt(65) r = a % b; > + return r; > +} > +#endif > + > +int > +main () > +{ > +#if __BITINT_MAXWIDTH__ >= 255 > + _BitInt(65) x = foo (); > + if (x != 0x0404040408080808wb) > + __builtin_abort (); > +#endif > +} > > Jakub > > -- Richard Biener SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg, Germany; GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)