From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 25655 invoked by alias); 8 Mar 2004 14:25:24 -0000 Mailing-List: contact gdb-patches-help@sources.redhat.com; run by ezmlm Precedence: bulk List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sources.redhat.com Received: (qmail 25601 invoked from network); 8 Mar 2004 14:25:22 -0000 Received: from unknown (HELO nevyn.them.org) (66.93.172.17) by sources.redhat.com with SMTP; 8 Mar 2004 14:25:22 -0000 Received: from drow by nevyn.them.org with local (Exim 4.30 #1 (Debian)) id 1B0Lh4-000413-5B; Mon, 08 Mar 2004 09:25:22 -0500 Date: Fri, 19 Mar 2004 00:09:00 -0000 From: Daniel Jacobowitz To: Richard Earnshaw Cc: gdb-patches@sources.redhat.com Subject: Re: [rfa/arm] Handle bx and blx Message-ID: <20040308142522.GA15288@nevyn.them.org> Mail-Followup-To: Richard Earnshaw , gdb-patches@sources.redhat.com References: <20040308140948.GA14686@nevyn.them.org> <200403081419.i28EJTH10164@pc960.cambridge.arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200403081419.i28EJTH10164@pc960.cambridge.arm.com> User-Agent: Mutt/1.5.1i X-SW-Source: 2004-03/txt/msg00153.txt.bz2 Message-ID: <20040319000900.hHm-qPN_jQ2l52yr_DPFzN8QWYxcjwY4kKnsTx_jdtg@z> On Mon, Mar 08, 2004 at 02:19:29PM +0000, Richard Earnshaw wrote: > > On Mon, Mar 08, 2004 at 10:17:53AM +0000, Richard Earnshaw wrote: > > > > On Wed, Mar 03, 2004 at 04:01:55PM +0000, Richard Earnshaw wrote: > > > > > > The software single-step implementation in GDB doesn't know either BX or > > > > > > BLX. This results in losing control of the inferior when we single-step > > > > > > over them. I based this on the ARM ARM, so I'm pretty sure I've got the > > > > > > numbers correct. > > > > > > > > > > > > OK to check in? > > > > > > > > > > > > -- > > > > > > Daniel Jacobowitz > > > > > > MontaVista Software Debian GNU/Linux Developer > > > > > > > > > > > > 2004-02-28 Daniel Jacobowitz > > > > > > > > > > > > * arm-tdep.c (thumb_get_next_pc): Handle BX. > > > > > > (arm_get_next_pc): Handle BX and BLX. > > > > > > > > > > Yikes! Yes, this is OK. However, Thumb has BLX (2 variants) as well. > > > > > > > > Right you are. I've checked in the above; if I'm reading > > > > thumb_get_next_pc and the ARM correctly, then the below is all I need > > > > for BLX. The first form is already handled since we don't check H. > > > > The second form can be handled identically to BX by relaxing a test. > > > > > > > > OK? > > > > > > > > -- > > > > Daniel Jacobowitz > > > > MontaVista Software Debian GNU/Linux Developer > > > > > > > > 2004-03-07 Daniel Jacobowitz > > > > > > > > * arm-tdep.c (thumb_get_next_pc): Handle Thumb BLX. > > > > > > Very close, and possibly good enough for most purposes. But the ARM ARM > > > says that in the blx(1) case, the resulting address should be masked with > > > 0xfffffffc. That means that there are two theoretical encodings for each > > > target ARM-state instruction. I think you need to add a test for H=01 and > > > if so, to apply the mask to nextpc. > > > > Except it also says: > > Bit[0] for BLX If H == 01, then bit[0] of the instruction must > > be zero, or the instruction is UNDEFINED. > > The offset calculation method described > > in Usage above ensures that the offset > > calculated for a BLX instruction is a > > multiple of four, and that this > > restriction is obeyed. > > > > So I think the mask really isn't needed, or am I reading that wrong? > > Ah, missed that bit. However, we could be starting with a pc value where > pc[1] != 0, so we still need the mask. Ahh, that's right. The offset will be a multiple of four but the PC+offset may not be. This OK then? -- Daniel Jacobowitz MontaVista Software Debian GNU/Linux Developer 2004-03-08 Daniel Jacobowitz * arm-tdep.c (thumb_get_next_pc): Handle Thumb BLX. Index: arm-tdep.c =================================================================== RCS file: /cvs/src/src/gdb/arm-tdep.c,v retrieving revision 1.165 diff -u -p -r1.165 arm-tdep.c --- arm-tdep.c 7 Mar 2004 20:03:12 -0000 1.165 +++ arm-tdep.c 8 Mar 2004 14:24:49 -0000 @@ -1651,13 +1651,16 @@ thumb_get_next_pc (CORE_ADDR pc) { nextpc = pc_val + (sbits (inst1, 0, 10) << 1); } - else if ((inst1 & 0xf800) == 0xf000) /* long branch with link */ + else if ((inst1 & 0xf800) == 0xf000) /* long branch with link, and blx */ { unsigned short inst2 = read_memory_integer (pc + 2, 2); offset = (sbits (inst1, 0, 10) << 12) + (bits (inst2, 0, 10) << 1); nextpc = pc_val + offset; + /* For BLX make sure to clear the low bits. */ + if (bits (inst2, 11, 12) == 1) + nextpc = nextpc & 0xfffffffc; } - else if ((inst1 & 0xff80) == 0x4700) /* branch and exchange (bx) */ + else if ((inst1 & 0xff00) == 0x4700) /* bx REG, blx REG */ { if (bits (inst1, 3, 6) == 0x0f) nextpc = pc_val;