From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 21853 invoked by alias); 29 Jul 2014 22:03:55 -0000 Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org Received: (qmail 21832 invoked by uid 89); 29 Jul 2014 22:03:51 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-3.2 required=5.0 tests=AWL,BAYES_00,RCVD_IN_DNSWL_LOW,RP_MATCHES_RCVD,SPF_PASS autolearn=ham version=3.3.2 X-HELO: mail-vc0-f170.google.com Received: from mail-vc0-f170.google.com (HELO mail-vc0-f170.google.com) (209.85.220.170) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES128-SHA encrypted) ESMTPS; Tue, 29 Jul 2014 22:03:49 +0000 Received: by mail-vc0-f170.google.com with SMTP id lf12so560017vcb.1 for ; Tue, 29 Jul 2014 15:03:47 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:date :message-id:subject:from:to:cc:content-type; bh=w+W2duNpWGitJuhAED5JHW90PSoZVqOYip36BmGuGYo=; b=Az0MfgJLuMjB2dJnAihmiZRQXINYlmbXZowG9dByhV7ZuCtBi1Cr7qXWzlzTg1BL1K 8GVDkh3atd2UR7gYNCgI8e5CE1Z1yE/n8vAuzUxXanGdhTKkB8+rR1etqZ9NjYQWVeQq ldhZz4kf1EaPXRGRI9USGCQsrxzEcQIu7rZMFPD9TrTvDCD7FT7CvN3ODvCVDjRioGnQ FFkpasZRtRwvjwNSiW49QcygRSKmISVuiqx9LEncgN7cJXQZt5hfpZn3Xivbw8v3bz1S KVZuvuO5Uh81eXi1crsnCKYLrGxk4u6qbl0iAsmmOOxQzDxtFzi3W7KPkL2iq2umKQNJ 19og== X-Gm-Message-State: ALoCoQkwEf0ADrvhATH2N56bMkCuYEgVuk8/uDH+x08m91ogxxzlR6EnCyqgz7Pn4LKtHuVLtHlu MIME-Version: 1.0 X-Received: by 10.220.192.129 with SMTP id dq1mr4778406vcb.57.1406671427202; Tue, 29 Jul 2014 15:03:47 -0700 (PDT) Received: by 10.52.28.233 with HTTP; Tue, 29 Jul 2014 15:03:47 -0700 (PDT) In-Reply-To: References: <1400878753-24688-1-git-send-email-palves@redhat.com> <538739A2.2050105@redhat.com> <20140701162830.GA25877@host2.jankratochvil.net> <1404291574.3766.35.camel@bordewijk.wildebeest.org> <53B3CDCC.9050502@redhat.com> <53B57911.10304@redhat.com> <53B6B0B8.2050702@redhat.com> <21434.52532.737427.778289@ruffy.mtv.corp.google.com> <53BC0D0B.7040001@redhat.com> <21437.28600.751354.629884@ruffy.mtv.corp.google.com> <53BD7749.5000800@redhat.com> Date: Tue, 29 Jul 2014 23:10:00 -0000 Message-ID: Subject: Re: [pushed+7.8] Re: [PATCH] Fix "attach" command vs user input race [Re: Regression for attach from stdin [Re: [pushed] Re: [PATCH v6 0/2] enable target-async by default]] From: Doug Evans To: Pedro Alves Cc: gdb-patches Content-Type: text/plain; charset=UTF-8 X-IsSubscribed: yes X-SW-Source: 2014-07/txt/msg00773.txt.bz2 On Tue, Jul 29, 2014 at 2:48 PM, Doug Evans wrote: > On Wed, Jul 9, 2014 at 10:09 AM, Pedro Alves wrote: >> On 07/09/2014 05:37 PM, Doug Evans wrote: >> >>> spurious change >> >> Fixed. >> >>> I like this a lot better. Thanks. >>> The patch is ok with me, modulo removing the spurious change. >> >> Here's what I pushed to both master and gdb-7.8-branch. >> >> Thanks. >> >> ------------- >> From 1fe2833b6dd03602ba86aa334e81466ea9abe66a Mon Sep 17 00:00:00 2001 >> From: Pedro Alves >> Date: Wed, 9 Jul 2014 17:52:58 +0100 >> Subject: [PATCH] Fix "attach" command vs user input race >> >> On async targets, a synchronous attach is done like this: >> >> #1 - target_attach is called (PTRACE_ATTACH is issued) >> #2 - a continuation is installed >> #3 - we go back to the event loop >> #4 - target reports stop (SIGSTOP), event loop wakes up, and >> attach continuation is called >> #5 - among other things, the continuation calls >> target_terminal_inferior, which removes stdin from the event >> loop >> >> Note that in #3, GDB is still processing user input. If the user is >> fast enough, e.g., with something like: >> >> echo -e "attach PID\nset xxx=1" | gdb >> >> ... then the "set" command is processed before the attach completes. >> >> We get worse behavior even, if input is a tty and therefore >> readline/editing is enabled, with e.g.,: >> >> (gdb) attach PID\nset xxx=1 >> >> we then crash readline/gdb, with: >> >> Attaching to program: attach-wait-input, process 14537 >> readline: readline_callback_read_char() called with no handler! >> Aborted >> $ >> >> Fix this by calling target_terminal_inferior before #3 above. >> >> The test covers both scenarios by running with editing/readline forced >> to both on and off. >> >> gdb/ >> 2014-07-09 Pedro Alves >> >> * infcmd.c (attach_command_post_wait): Don't call >> target_terminal_inferior here. >> (attach_command): Call it here instead. >> >> gdb/testsuite/ >> 2014-07-09 Pedro Alves >> >> * gdb.base/attach-wait-input.exp: New file. >> * gdb.base/attach-wait-input.c: New file. > > Hi. > > Is this TODO still needed after this patch? > > infcmd.c: > > /* > * TODO: > * Should save/restore the tty state since it might be that the > * program to be debugged was started on this tty and it wants > * the tty in some state other than what we want. If it's running > * on another terminal or without a terminal, then saving and > * restoring the tty state is a harmless no-op. > * This only needs to be done if we are attaching to a process. > */ A related issue (or the same one if one prefers): post_create_inferior does this: /* Be sure we own the terminal in case write operations are performed. */ target_terminal_ours (); but post_create_inferior is called *after* target_post_attach in attach_command_post_wait: /* Take any necessary post-attaching actions for this platform. */ target_post_attach (ptid_get_pid (inferior_ptid)); post_create_inferior (¤t_target, from_tty); What if target_post_attach does some writes? Seems like it can, e.g., some of the ptrace checking stuff may print a warning. Plus attach_command_post_wait calls some other stuff before post_create_inferior that could cause some writes to the terminal. Question: Is there a specific terminal state that needs to be in effect when attach_command_post_wait returns? Or can we just call target_terminal_ours at its start? [and leave it to other code to switch back to target_terminal_inferior as needed - e.g. proceed calls resume which will call target_terminal_inferior]