From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 101565 invoked by alias); 29 Apr 2015 15:54:16 -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 101548 invoked by uid 89); 29 Apr 2015 15:54:15 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.9 required=5.0 tests=AWL,BAYES_00,SPF_HELO_PASS,SPF_PASS,T_RP_MATCHES_RCVD autolearn=ham version=3.3.2 X-HELO: mx1.redhat.com Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES256-GCM-SHA384 encrypted) ESMTPS; Wed, 29 Apr 2015 15:54:15 +0000 Received: from int-mx11.intmail.prod.int.phx2.redhat.com (int-mx11.intmail.prod.int.phx2.redhat.com [10.5.11.24]) by mx1.redhat.com (Postfix) with ESMTPS id 032929174D for ; Wed, 29 Apr 2015 15:54:13 +0000 (UTC) Received: from [127.0.0.1] (ovpn01.gateway.prod.ext.ams2.redhat.com [10.39.146.11]) by int-mx11.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id t3TFsCTQ000492; Wed, 29 Apr 2015 11:54:13 -0400 Message-ID: <5540FEA3.7050406@redhat.com> Date: Wed, 29 Apr 2015 18:19:00 -0000 From: Pedro Alves User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 MIME-Version: 1.0 To: Jan Kratochvil , gdb-patches@sourceware.org CC: Phil Muldoon Subject: Re: [PATCH v3 9/9] compile: compile printf: gdbserver support References: <20150411194322.29128.52477.stgit@host1.jankratochvil.net> <20150411194437.29128.58569.stgit@host1.jankratochvil.net> <20150426093318.GA6765@host1.jankratochvil.net> In-Reply-To: <20150426093318.GA6765@host1.jankratochvil.net> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-SW-Source: 2015-04/txt/msg01080.txt.bz2 On 04/26/2015 10:33 AM, Jan Kratochvil wrote: > On Sat, 11 Apr 2015 21:44:37 +0200, Jan Kratochvil wrote: >> former patch injects plain: >> printf (...); >> This patch injects gdbserver-compatible: >> f = open_memstream (&s, ...); >> fprintf (f, ...); >> fclose (f); >> return s; > > I have realized this print+printf patchset introduces calling inferior > implicit malloc() + explicit free() (by free_inferior_memory) which the > original 'compile code' series avoided (using gdbarch_infcall_mmap() instead). > The goal was not to crash the inferior futher with print commands when > analyzing corrupted inferior memory lists. Right. The "compile code" infrastructure should restrict itself to async-signal-safe functions for its internal mechanisms for that reason. Of course, if the expression the user injects runs non-async-signal-safe at the wrong time, the user gets what she asked for. > > I somehow expected that printf()/fprintf() are so heavyweight they will call > malloc() on their own so this mmap goal is no longer achievable for printf. > But I have found now glibc in most real world cases uses just alloca(). > > The problem is even calling fmemopen() instead of open_memstream() still > implicitly calls malloc() - for fmemopen_cookie_t and for FILE. > > The only idea I have is to redirect by a breakpoint glibc's implicit calls to > malloc() into GDB's allocator by inferior mmap. But that seems a bit ugly. Using mmap along with snprintf would be safer, but given that snprintf is not async-signal-safe in general either, it's fine with me to leave this as you have it. I think the manual should say that the command internally may call functions that are not async-signal-safe though. > So currently keeping it as a known bug. Otherwise looks good to me. Thanks, Pedro Alves