From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 25980 invoked by alias); 21 Oct 2014 20:34:59 -0000 Mailing-List: contact gdb-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-owner@sourceware.org Received: (qmail 25891 invoked by uid 89); 21 Oct 2014 20:34:58 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.0 required=5.0 tests=AWL,BAYES_00,RCVD_IN_DNSWL_NONE autolearn=ham version=3.3.2 X-HELO: relay1.mentorg.com Received: from relay1.mentorg.com (HELO relay1.mentorg.com) (192.94.38.131) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Tue, 21 Oct 2014 20:34:56 +0000 Received: from nat-ies.mentorg.com ([192.94.31.2] helo=SVR-IES-FEM-01.mgc.mentorg.com) by relay1.mentorg.com with esmtp id 1Xgg8r-0001Jo-19 from Maciej_Rozycki@mentor.com ; Tue, 21 Oct 2014 13:34:53 -0700 Received: from localhost (137.202.0.76) by SVR-IES-FEM-01.mgc.mentorg.com (137.202.0.104) with Microsoft SMTP Server (TLS) id 14.3.181.6; Tue, 21 Oct 2014 21:34:51 +0100 Date: Tue, 21 Oct 2014 20:34:00 -0000 From: "Maciej W. Rozycki" To: Christopher Bainbridge CC: Subject: Re: [help] Issues with 'g' packet and MIPS - gdb interprets the packet reply wrong In-Reply-To: <54464055.9020100@my.bristol.ac.uk> Message-ID: References: <54464055.9020100@my.bristol.ac.uk> User-Agent: Alpine 1.10 (DEB 962 2008-03-14) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" X-SW-Source: 2014-10/txt/msg00085.txt.bz2 Hi Christopher, > I am trying to implement a remote stub for a MIPS cpu (using GDB version 7.8). > When GDB asks for the general registers using the 'g' packet, I reply with: > > 00000000000000000d01000000000000fffdffff00000000000000000080c0bf30000000f0fec0bf000000002e0000000000000000000000000000008080808000000000000000000000000000000000000000000000000000000000000000000000000000000000000001800000000000000000e8fec0bf00000000702ec0bf0000000000000000000000000000000000000000702ec0bf > > As each register is 32 bits (represented by 8 hex characters), this should be > all the registers up to and including the PC. What makes you assume the registers are 32 bits each? > However, GDB prints this out: > > info reg > zero at v0 v1 a0 a1 a2 a3 > R0 00000000 0000010d fffffdff 00000000 00000030 00000000 00000000 00000000 > t0 t1 t2 t3 t4 t5 t6 t7 > R8 00000000 00000000 00000000 00000000 00000000 80010000 00000000 00000000 > s0 s1 s2 s3 s4 s5 s6 s7 > Sending packet: $p13#d4...Ack > Packet received: 00000000 > Sending packet: $p14#d5...Ack > Packet received: 00000000 > Sending packet: $p15#d6...Ack > Packet received: 00000000 > Sending packet: $p16#d7...Ack > Packet received: 00000000 > Sending packet: $p17#d8...Ack > Packet received: 00000000 > R16 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 > t8 t9 k0 k1 gp sp s8 ra > Sending packet: $p18#d9...Ack > Packet received: 00000000 > Sending packet: $p19#da...Ack > Packet received: 00000000 > Sending packet: $p1a#02...Ack > Packet received: 00000180 > Sending packet: $p1b#03...Ack > > etc > > This looks to be that it is determining the size of each register incorrectly, > and is thus asking for more registers using the 'p' packet. > > Is this a bug on my end or in GDB? > I use the command > > set processor mips:14000 > > beforehand, as this is the processor we're using. You mean: (gdb) set architecture mips:14000 I presume, right? The R14000 is a 64-bit processor so its registers are 64-bit and will be treated as such by default by GDB. You may be able to limit the width of registers expected by selecting a 32-bit processor instead or by selecting a 32-bit ABI such as `o32'. The latter can be done with: (gdb) set mips abi o32 or by selecting a file to debug that has been built for that ABI. Please note that this is a grey area though, with a bare-metal stub you should be really exchanging registers with GDB in their native sizes and letting GDB truncate and extend them as required depending on the ABI used by the program being debugged. GDB is already capable of doing that, however in order to make use of that capability both the stub and GDB would have to support XML register descriptions which is something that owing to the vast number of CP0 register set variants in the MIPS architecture has never been implemented. So in fact you may be hitting problems regardless of the ABI selection noted above. You can always determine the widths of registers GDB expects with the: (gdb) maintenance print registers command -- see the `Type' column on the right for the internal type used and note that the registers exchanged with a remote stub are those in the low half of indices (`Nr' == `Rel'), the so called "raw registers". HTH, Maciej