From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from simark.ca by simark.ca with LMTP id 7ORkAX9zpGomjAEAWB0awg (envelope-from ) for ; Fri, 11 Sep 2026 17:32:47 -0400 Authentication-Results: simark.ca; dkim=pass (1024-bit key; unprotected) header.d=suse.de header.i=@suse.de header.a=rsa-sha256 header.s=susede2_rsa header.b=neFdugWw; dkim=pass header.d=suse.de header.i=@suse.de header.a=ed25519-sha256 header.s=susede2_ed25519 header.b=Dx/lLMd0; dkim=pass (1024-bit key) header.d=suse.de header.i=@suse.de header.a=rsa-sha256 header.s=susede2_rsa header.b=MyMhmtMb; dkim=neutral header.d=suse.de header.i=@suse.de header.a=ed25519-sha256 header.s=susede2_ed25519 header.b=tCKTi3mJ; dkim-atps=neutral Received: by simark.ca (Postfix, from userid 112) id E17211E09E; Fri, 11 Sep 2026 17:32:46 -0400 (EDT) X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-25) on simark.ca X-Spam-Level: X-Spam-Status: No, score=-2.4 required=5.0 tests=ARC_SIGNED,ARC_VALID,BAYES_00, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED,RCVD_IN_VALIDITY_CERTIFIED_BLOCKED, RCVD_IN_VALIDITY_RPBL_BLOCKED,RCVD_IN_VALIDITY_SAFE_BLOCKED autolearn=ham autolearn_force=no version=4.0.1 Received: from vm01.sourceware.org (vm01.sourceware.org [38.145.34.32]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange x25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by simark.ca (Postfix) with ESMTPS id 1638B1E033 for ; Fri, 11 Sep 2026 17:32:45 -0400 (EDT) Received: from vm01.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id AF1DA48A081A for ; Fri, 11 Sep 2026 21:32:43 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org AF1DA48A081A Authentication-Results: sourceware.org; dkim=pass (1024-bit key, unprotected) header.d=suse.de header.i=@suse.de header.a=rsa-sha256 header.s=susede2_rsa header.b=neFdugWw; dkim=pass header.d=suse.de header.i=@suse.de header.a=ed25519-sha256 header.s=susede2_ed25519 header.b=Dx/lLMd0; dkim=pass (1024-bit key) header.d=suse.de header.i=@suse.de header.a=rsa-sha256 header.s=susede2_rsa header.b=MyMhmtMb; dkim=neutral header.d=suse.de header.i=@suse.de header.a=ed25519-sha256 header.s=susede2_ed25519 header.b=tCKTi3mJ Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.223.130]) by sourceware.org (Postfix) with ESMTPS id EA8274BC7EDE for ; Fri, 11 Sep 2026 21:32:16 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org EA8274BC7EDE 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 EA8274BC7EDE Authentication-Results: sourceware.org; arc=none smtp.remote-ip=195.135.223.130 ARC-Seal: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1789162337; cv=none; b=rZRZlQNY8w9dIRoQ27YvTQqQjmGmgHkM2wzoE4HX7UQr0DqCOVf46K4Rg/z7ySvyld6kkyTWS7ppM3wyOSElOlI/Id6cLPpTclOL0oaEbhrM831VZnYwbRJ9n9kIXFrfZGscIW0G8LbOq167GHXy+oqXxnOV8TGQfAu9WGxeXq0= ARC-Message-Signature: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1789162337; c=relaxed/simple; bh=awdiZIvc8TyvXFqHXbTSVoA0CA1WdMvkKtpBFLsEmxc=; h=DKIM-Signature:DKIM-Signature:DKIM-Signature:DKIM-Signature: Message-ID:Date:MIME-Version:Subject:To:From; b=raABAcpZSBTSrnirCbP31Z0k0g0k6mTtcPopKU3bixmcIAGWYbzF4qIWggFI98CFVOeXCzaZqafUmx2Oq9XOiAc1MWrH8kL0uLZj1AQVFrqKCSuiV/0v9Fcmh/ZJw9ifUg8HTN0EA7r/RERcha6gmstvS170Q6/6w29dzGsrj1I= ARC-Authentication-Results: i=1; sourceware.org; dkim=pass (1024-bit key, unprotected) header.d=suse.de header.i=@suse.de header.a=rsa-sha256 header.s=susede2_rsa header.b=neFdugWw; dkim=pass header.d=suse.de header.i=@suse.de header.a=ed25519-sha256 header.s=susede2_ed25519 header.b=Dx/lLMd0; dkim=pass (1024-bit key) header.d=suse.de header.i=@suse.de header.a=rsa-sha256 header.s=susede2_rsa header.b=MyMhmtMb; dkim=neutral header.d=suse.de header.i=@suse.de header.a=ed25519-sha256 header.s=susede2_ed25519 header.b=tCKTi3mJ DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org EA8274BC7EDE Received: from imap1.dmz-prg2.suse.org (imap1.dmz-prg2.suse.org [IPv6:2a07:de40:b281:104:10:150:64:97]) (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 66ED521DB4; Fri, 11 Sep 2026 21:32:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1789162331; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=/g17XdKJU4VhSwldDKT1+Mktgla+9j8jwxcDvvITC54=; b=neFdugWwfynlXVvUkeZhp104spqDDDAr1rZ+xpRT7RrF4DGapeHkxW+xwXVnUCQXkyLqGV taVcPBX8ltM+/HsFXdtLnUyto3voZWKQ0qkSaPSVVi5ads5iUk2fSiuECfhKuhLN5nS4mk S7iuZw2BfCLdEicV2sBjTBU7F92Wnhg= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1789162331; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=/g17XdKJU4VhSwldDKT1+Mktgla+9j8jwxcDvvITC54=; b=Dx/lLMd0YkUbAGeSFp2zhOLnm07K7fIvDYgtzlOzh5ZnXQ/tdXJkssbt6M8k6H0ra/a8JY jfcSgc8lxi0tyZBw== Authentication-Results: smtp-out1.suse.de; dkim=pass header.d=suse.de header.s=susede2_rsa header.b=MyMhmtMb; dkim=pass header.d=suse.de header.s=susede2_ed25519 header.b=tCKTi3mJ DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1789162327; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=/g17XdKJU4VhSwldDKT1+Mktgla+9j8jwxcDvvITC54=; b=MyMhmtMboEJkw5nsvzfWXWaOajYVWZFl2dn31zmKRNtjBLRz3f9dUje4VeqkEDjOyYWFtW SPRGJSy6aqFcNYLIudZJhBlCeh0JlyKzOdbO06FZUWc2IiEqjz48hXK8O2SR8b0+UNslDa qU0CPH2wMO6DvgMkT+Axn3xhpsoqFu4= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1789162327; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=/g17XdKJU4VhSwldDKT1+Mktgla+9j8jwxcDvvITC54=; b=tCKTi3mJJxDpY2atT6kwtq318ORskwZt9gC9R9lwEciU+luzwBSYSxMdz6DOIrV+nypDqn LIijP1rKApxbKgDw== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (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 imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id 33468136ED; Fri, 11 Sep 2026 21:32:07 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id TEnMCVdzpGqIJQAAD6G6ig (envelope-from ); Fri, 11 Sep 2026 21:32:07 +0000 Message-ID: Date: Fri, 11 Sep 2026 23:32:06 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] Rewrite gdb_mpz::export_bits To: Tom Tromey Cc: gdb-patches@sourceware.org References: <20260909180822.2255847-1-tromey@adacore.com> <875x0d0w41.fsf@tromey.com> Content-Language: en-US From: Tom de Vries In-Reply-To: <875x0d0w41.fsf@tromey.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 66ED521DB4 X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Rspamd-Action: no action X-Spamd-Result: default: False [-4.51 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; MID_RHS_MATCH_FROM(0.00)[]; TO_DN_SOME(0.00)[]; RCPT_COUNT_TWO(0.00)[2]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[buf.data:url,sourceware.org:url,imap1.dmz-prg2.suse.org:helo,imap1.dmz-prg2.suse.org:rdns,suse.de:dkim,suse.de:mid,adacore.com:email]; DKIM_TRACE(0.00)[suse.de:+] X-BeenThere: gdb-patches@sourceware.org X-Mailman-Version: 2.1.30 Precedence: list List-Id: Gdb-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: gdb-patches-bounces~public-inbox=simark.ca@sourceware.org On 9/10/26 9:01 PM, Tom Tromey wrote: > Tom> If so, I prefer "truncated" to "masked". > > I changed the name. > >>> + if (sign < 0 && masked.sgn () != 0) > > Tom> I think it's clearer to do this, because there's less state to keep > Tom> going forward: > Tom> ... > Tom> if (masked.sgn () == 0) > Tom> { > Tom> memset (buf.data (), 0, buf.size ()); > Tom> return; > Tom> } > > Tom> if (sign < 0) > Tom> ... > > Tom> This starts to get verbose, but after factoring out some lambda functions: > > I don't like lambda functions in a situation like this. IMO they often > just obfuscate the code. > > Instead I rearranged the code a bit in v2. > This makes it a little simpler. I see. LGTM. Thanks, - Tom > Tom > > commit b107ae9e505d14a46211dd6832b69b8bd70fc16b > Author: Tom Tromey > Date: Wed Sep 9 11:22:04 2026 -0600 > > Rewrite gdb_mpz::export_bits > > A couple of bugs point out that, when multiplication overflows, gdb > does not compute the correct result. This is caused by some bugs in > gdb_mpz::export_bits. This patch rewrites part of this function, > hopefully now getting the correct answer. I think the new code should > be somewhat simpler to follow. > > A new selftest is added, derived from the code in the bug report. > > This rewrite doesn't try to minimize allocations, the way the previous > one did. I tend to doubt that matters, and this is one of the > readability improvements IMO. > > Regression tested on x86-64 Fedora 43. > > I am not sure but it might be worth applying this to gdb 18; your > thoughts appreciated. > > Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=34601 > > diff --git a/gdb/gmp-utils.c b/gdb/gmp-utils.c > index b7fed9a82d1..21f474798eb 100644 > --- a/gdb/gmp-utils.c > +++ b/gdb/gmp-utils.c > @@ -128,38 +128,24 @@ gdb_mpz::export_bits (gdb::array_view buf, int endian, bool unsigned_p > hi.str ().c_str ()); > } > > - const gdb_mpz *exported_val = this; > - gdb_mpz un_signed; > - if (sign < 0) > - { > - /* mpz_export does not handle signed values, so create a positive > - value whose bit representation as an unsigned of the same length > - would be the same as our negative value. */ > - gdb_mpz neg_offset = gdb_mpz::pow (2, buf.size () * HOST_CHAR_BIT); > - un_signed = *exported_val + neg_offset; > - exported_val = &un_signed; > - } > + gdb_mpz truncated = *this; > + truncated.mask (buf.size () * HOST_CHAR_BIT); > > - /* If the value is too large, truncate it. */ > - if (!safe > - && mpz_sizeinbase (exported_val->m_val, 2) > buf.size () * HOST_CHAR_BIT) > + /* It's possible that the above results in zero, which has to be > + handled specially. */ > + if (truncated.sgn () == 0) > { > - /* If we don't already have a copy, make it now. */ > - if (exported_val != &un_signed) > - { > - un_signed = *exported_val; > - exported_val = &un_signed; > - } > - > - un_signed.mask (buf.size () * HOST_CHAR_BIT); > + memset (buf.data (), 0, buf.size ()); > + return; > } > > - /* It's possible that one of the above results in zero, which has to > - be handled specially. */ > - if (exported_val->sgn () == 0) > + if (sign < 0) > { > - memset (buf.data (), 0, buf.size ()); > - return; > + /* mpz_export does not handle signed values, so create a > + positive value whose bit representation as an unsigned of the > + same length would be the same as our negative value. */ > + gdb_mpz neg_offset = gdb_mpz::pow (2, buf.size () * HOST_CHAR_BIT); > + truncated += neg_offset; > } > > /* Do the export into a buffer allocated by GMP itself; that way, > @@ -174,8 +160,9 @@ gdb_mpz::export_bits (gdb::array_view buf, int endian, bool unsigned_p > > size_t word_countp; > gdb::unique_xmalloc_ptr exported > - (mpz_export (NULL, &word_countp, -1 /* order */, buf.size () /* size */, > - endian, 0 /* nails */, exported_val->m_val)); > + (mpz_export (nullptr, &word_countp, -1 /* order */, > + buf.size () /* size */, endian, 0 /* nails */, > + truncated.m_val)); > > gdb_assert (word_countp == 1); > > diff --git a/gdb/unittests/gmp-utils-selftests.c b/gdb/unittests/gmp-utils-selftests.c > index 1912d346c17..417abae5463 100644 > --- a/gdb/unittests/gmp-utils-selftests.c > +++ b/gdb/unittests/gmp-utils-selftests.c > @@ -80,6 +80,12 @@ gdb_mpz_as_integer () > v -= 1; > > SELF_CHECK (v.as_integer () == ul_expected); > + > + /* This is from PR gdb/34601. */ > + LONGEST neg = (LONGEST) 0x8000000000000001ull; > + gdb_mpz a (neg); > + gdb_mpz b (0x1234); > + SELF_CHECK ((a * b).as_integer_truncate () == 0x1234); > } > > /* A helper function which calls the given gdb_mpz object's as_integer