From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.freebsd.org (mx2.freebsd.org [96.47.72.81]) by sourceware.org (Postfix) with ESMTPS id 70C5D3857C4A for ; Tue, 31 May 2022 16:08:19 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 70C5D3857C4A Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=FreeBSD.org Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) client-signature RSA-PSS (4096 bits)) (Client CN "mx1.freebsd.org", Issuer "R3" (verified OK)) by mx2.freebsd.org (Postfix) with ESMTPS id 4C5607C11D; Tue, 31 May 2022 16:08:19 +0000 (UTC) (envelope-from jhb@FreeBSD.org) Received: from smtp.freebsd.org (smtp.freebsd.org [IPv6:2610:1c1:1:606c::24b:4]) (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 client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "smtp.freebsd.org", Issuer "R3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 4LCHJ31SN6z4hk6; Tue, 31 May 2022 16:08:19 +0000 (UTC) (envelope-from jhb@FreeBSD.org) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=freebsd.org; s=dkim; t=1654013299; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ebpBg+0Ixv00+OOfbwOucdeIS2Kqwe8nCKKgG5Nu3HM=; b=iSpm6AZwIH52NFkYJzZXpGNAK3jgiknRP8F5hRSSnvoZxhjsXFDHR4k4ejiTl6iju1v9qR 8SbyACcqLMy5JEFvx+8tWVtpf8ThA4L51J7FT7/rlpiTD35uu8FZK3m7MQ+3DYzpMSyN8M pMuIb2EtAXE8EAhpxssJzOMeyX5fenx1yCdiiFMjD8Z7nnRQRb/fQNCJiiAzOmxQC5iAcN p08l5YghD3mhhrv1TUcJgpeHn48Gl4R4eacWtvpu3t7GkuFFSiHzvo2hklgtVt5+3jEAf2 sEbUc0rPIZw3thAoOrtA3r127kbGgsYuU44DlnD6/I+5Zxq6cQnoKoOVnBKInw== Received: from [10.0.1.4] (ralph.baldwin.cx [66.234.199.215]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client did not present a certificate) (Authenticated sender: jhb) by smtp.freebsd.org (Postfix) with ESMTPSA id C1B792C984; Tue, 31 May 2022 16:08:18 +0000 (UTC) (envelope-from jhb@FreeBSD.org) Message-ID: <71a986a5-2cfa-543e-4034-70f3af7dfecf@FreeBSD.org> Date: Tue, 31 May 2022 09:08:17 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:91.0) Gecko/20100101 Thunderbird/91.9.0 Subject: Re: [PATCH 5/5] gdb: native target invalid architecture detection Content-Language: en-US To: Andrew Burgess , gdb-patches@sourceware.org References: From: John Baldwin In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=freebsd.org; s=dkim; t=1654013299; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ebpBg+0Ixv00+OOfbwOucdeIS2Kqwe8nCKKgG5Nu3HM=; b=KRzrURAd+NANXjDIJx6qPzDIEf98WikMvo0sO+kbrMy0mMKYhk9lmuA58LKJwAPiWHY+vf AvhJt5K9PJxogoxoFfB241E7rTuEBBobIn/PL8N55G3inI6BxHRa7RSLJxFSMKQmm6i2sC hw1yzpMgZTOxRAHnLx42yly9oel2y9km80oD4+mqEmaqnkZYKvKq3otDKj6YXmNy+NZ/Gh pUKWTRtSwpyl8McR29kEUsGMAdABsht+6dSkoPyfMxwkiLjrxRNOgt3WAzBwhRl4rwNQhX LHJB7LlgkGazOP2PsmO+bjsYIgToZYGYUOris4GMdYzVAOd6MF3VMyhNEHJ0ow== ARC-Seal: i=1; s=dkim; d=freebsd.org; t=1654013299; a=rsa-sha256; cv=none; b=JKe+gg3N8t1M9usluXiCKvExWexibiXSZWU4Ov+n8387+4MiM/uTr3NCnrG3F9AIWIa30U Lvl1EeJIAj9/6e4ySxnqCYk7a2po1dSPVPop82lzFp6fnBmgQjJJkWkDWq+reu9Qvjm/+u oTQBwwTqtpUZqGoY0v6As+uoRJmKBii/haRs9lP7R9V+p0kTX4ZiLR+9yQ4dde5pFW/q+8 lpfZ4SshM8ubW+CH7drYwXWrep54xfQ1DL9BifMCtufWav+GgkcBGJl9JjsSi3XPwIc1+r 0QJr3z/sAd4vgkHVuI40hzW13aKCwnlEasf4VPPc222ihFwXYd00cj5Q5r0nIg== ARC-Authentication-Results: i=1; mx1.freebsd.org; none X-Spam-Status: No, score=-6.6 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, NICE_REPLY_A, SPF_HELO_NONE, SPF_PASS, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: gdb-patches@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gdb-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 31 May 2022 16:08:21 -0000 On 5/31/22 7:30 AM, Andrew Burgess via Gdb-patches wrote: > If GDB is asked to start a new inferior, or attach to an existing > process, using a binary file for an architecture that does not match > the current native target, then, currently, GDB will assert. Here's > an example session using current HEAD of master with GDB built for an > x86-64 GNU/Linux native target, the binary being used is a RISC-V ELF: > > $ ./gdb/gdb -q --data-directory ./gdb/data-directory/ > (gdb) file /tmp/hello.rv32imc.x > Reading symbols from /tmp/hello.rv32imc.x... > (gdb) start > Temporary breakpoint 1 at 0x101b2: file hello.rv32.c, line 23. > Starting program: /tmp/hello.rv32imc.x > ../../src/gdb/gdbarch.h:166: internal-error: gdbarch_tdep: Assertion `dynamic_cast (tdep) != nullptr' failed. > A problem internal to GDB has been detected, > further debugging may prove unreliable. > > The same error is encountered if, instead of starting a new inferior, > the user tries to attach to an x86-64 process with a RISC-V binary set > as the current executable. > > These errors are not specific to the x86-64/RISC-V pairing I'm using > here, any attempt to use a binary for one architecture with a native > target of a different architecture will result in a similar error. > > Clearly, attempting to use this cross-architecture combination is a > user error, but I think GDB should do better than an assert; ideally a > nice error should be printed. > > The problem we run into is that, when the user starts a new inferior, > or attaches to an inferior, the inferior stops. At this point GDB > attempts to handle the stop, and this involves reading registers from > the inferior. > > These register reads end up being done through the native target, so > in the example above, we end up in the amd64_supply_fxsave function. > However, these functions need a gdbarch. The gdbarch is fetched from > the register set, which was constructed using the gdbarch from the > binary currently in use. And so we end up in amd64_supply_fxsave > using a RISC-V gdbarch. > > When we call: > > i386_gdbarch_tdep *tdep = gdbarch_tdep (gdbarch); > > this will assert as the gdbarch_tdep data within the RISC-V gdbarch is > of the type riscv_gdbarch_tdep not i386_gdbarch_tdep. > > The solution I propose in this commit is to add a new target_ops > method supports_architecture_p. This method will return true if a > target can safely be used with a specific architecture, otherwise, the > method returns false. > > I imagine that a result of true from this method doesn't guarantee > that GDB can start an inferior of a given architecture, it just means > that GDB will not crash if such an attempt is made. A result of false > is a hard stop; attempting to use this target with this architecture > is not supported, and may cause GDB to crash. > > This distinction is important I think for things like remote targets, > and possibly simulator targets. We might imagine that GDB can ask a > remote (or simulator) to start with a particular executable, and the > target might still refuse for some reason. But my thinking is that > these refusals should be well handled (i.e. GDB should give a user > friendly error), rather than crashing, as is the case with the native > targets. > > For example, if I start gdbserver on an x86-64 machine like this: > > gdbserver --multi :54321 > > Then make use of this from a GDB session like this: > > $ ./gdb/gdb -q --data-directory ./gdb/data-directory/ > (gdb) file /tmp/hello.rv32imc.x > Reading symbols from /tmp/hello.rv32imc.x... > (gdb) target extended-remote :54321 > Remote debugging using :54321 > (gdb) run > Starting program: /tmp/hello.rv32imc.x > Running the default executable on the remote target failed; try "set remote exec-file"? > (gdb) > > Though the error is not very helpful in diagnosing the problem, we can > see that GDB has not crashed, but has given the user an error. > > And so, the supports_architecture_p method is created to return true > by default, then I override this in inf_child_target, where I compare > the architecture in question with the default_bfd_arch. > > Finally, I've added calls to supports_architecture_p for the > run (which covers run, start, starti) and attach commands. > > You will notice a lack of tests for this change. I'm not sure of a > good way that I can build a binary for a different architecture as > part of a test, but if anyone has any ideas then I'll be happy to add > a test here. Have you considered multi-arch cases such as running i386 binaries on an x86-64 host or 32-bit arm binaries on an AArch64 host? Will we need to override this method in certain targets (e.g. x86-linux-nat.c or x86-fbsd-nat.c) to support such cases? -- John Baldwin