From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from simark.ca by simark.ca with LMTP id p5kEKpLqj2AdQAAAWB0awg (envelope-from ) for ; Mon, 03 May 2021 08:20:34 -0400 Received: by simark.ca (Postfix, from userid 112) id 9F8171F11C; Mon, 3 May 2021 08:20:34 -0400 (EDT) X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on simark.ca X-Spam-Level: X-Spam-Status: No, score=-1.0 required=5.0 tests=MAILING_LIST_MULTI, URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.2 Received: from sourceware.org (server2.sourceware.org [8.43.85.97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by simark.ca (Postfix) with ESMTPS id 9BBC51E54D for ; Mon, 3 May 2021 08:20:33 -0400 (EDT) Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id 2FDE9394FC3A; Mon, 3 May 2021 12:20:33 +0000 (GMT) Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by sourceware.org (Postfix) with ESMTPS id 622AA394FC3A for ; Mon, 3 May 2021 12:20:30 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 622AA394FC3A Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=suse.de Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=tdevries@suse.de X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 82AB0AE00; Mon, 3 May 2021 12:20:29 +0000 (UTC) Subject: Re: [PATCH][gdb/guile] Don't allow libguile to change libgmp mem fns To: Andrew Burgess References: <20210503085428.GA20738@delia> <20210503111842.GA6612@embecosm.com> From: Tom de Vries Message-ID: <39526c4b-8de7-c804-baa9-5babe6b05c5e@suse.de> Date: Mon, 3 May 2021 14:20:28 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.9.1 MIME-Version: 1.0 In-Reply-To: <20210503111842.GA6612@embecosm.com> Content-Type: multipart/mixed; boundary="------------19F87ED6182D75C9DCA2CBC3" Content-Language: en-US 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: , Cc: =?UTF-8?Q?Ludovic_Court=c3=a8s?= , gdb-patches@sourceware.org Errors-To: gdb-patches-bounces@sourceware.org Sender: "Gdb-patches" This is a multi-part message in MIME format. --------------19F87ED6182D75C9DCA2CBC3 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit On 5/3/21 1:18 PM, Andrew Burgess wrote: > * Tom de Vries [2021-05-03 10:54:29 +0200]: > >> Hi, >> >> Since gdb commit 880ae75a2b7 "gdb delay guile initialization until >> gdbscm_finish_initialization" I'm running into: >> ... >> (gdb) print My_Var > 10.0^M >> free(): invalid pointer^M >> ERROR: GDB process no longer exists >> GDB process exited with wait status 5995 exp9 0 0 CHILDKILLED SIGABRT SIGABRT >> UNRESOLVED: gdb.ada/fixed_cmp.exp: gnat_encodings=all: print My_Var > 10.0 >> ... >> >> The problem is that both gdb and libguile try to set the libgmp memory functions, >> and since the gdb commit the ones from libguile are effective, which results >> in gdb freeing some memory in a way that is not compatible with the way that >> memory was actually allocated. >> >> The fact that libguile tries to set the libgmp memory functions is a bug which >> should be fixed starting version v3.0.6. >> >> Meanwhile, work around this in gdb by not allowing libguile to set the libgomp >> memory functions. > > Thanks for looking into this, and sorry for causing the breakage. > Price of progress I'd say :) > I had a read through the bug, and this solution seems to make sense, > however, I had two thoughts. > > First, I already had to solve a similar problem for Python when doing > this work. For Python the issue related to which signal handlers were > installed. > > Though the problem was Python specific, I figured that it was cleaner > to make the solution generic, so I placed the fix in > gdb/extension.c:ext_lang_initialization - look for the use of > scoped_default_sigint. > > I wonder if this fix should similarly be placed at this level? I'll > leave this choice up to you, I don't feel strongly on this, but > thought it might be worth mentioning. > Thanks for mentioning that. I've thought about it for a bit, and I haven't convinced myself that it's a better idea to do this one level up. That is: I'm now working around a known bug. Increasing the scope of the workaround means that it will workaround bugs in other components, possible unknown ones, which we'd like to know about. So for now I'm leaving the workaround where it is. FWIW, perhaps what could be done at a larger scope regardless is checking. So, currently we have: ... void _initialize_gmp_utils () { /* Tell GMP to use GDB's memory management routines. */ mp_set_memory_functions (xmalloc, xrealloc_for_gmp, xfree_for_gmp); } ... and we could add some: ... void _verify_gmp_utils () { /* Tell GMP to use GDB's memory management routines. */ mp_get_memory_functions (&f1, &f2, &f3); gdb_assert (f1 == xmalloc && f2 == xrealloc_for_gmp && f3 == xfree_for_gmp); } ... and use _initialize_gmp_utils () to add _verify_gmp_utils to some verify hook list that is checked at some appropiate time(s). > For the second thought, see below... > >> >> Tested on x86_64-linux. >> >> Any comments? >> >> Thanks, >> - Tom >> >> [gdb/guile] Don't allow libguile to change libgmp mem fns >> >> gdb/ChangeLog: >> >> 2021-05-03 Tom de Vries >> >> PR guile/27806 >> * guile/guile.c (gdbscm_initialize): Save and restore libgmp memory >> functions. >> >> --- >> gdb/guile/guile.c | 22 ++++++++++++++++++++++ >> 1 file changed, 22 insertions(+) >> >> diff --git a/gdb/guile/guile.c b/gdb/guile/guile.c >> index bdf15cd498b..6ee8b3f47ce 100644 >> --- a/gdb/guile/guile.c >> +++ b/gdb/guile/guile.c >> @@ -662,10 +662,32 @@ gdbscm_initialize (const struct extension_language_defn *extlang) >> { >> gdb::block_signals blocker; >> >> + /* There are libguile versions (f.i. v3.0.5) that by default call >> + mp_get_memory_functions during initialization to install custom >> + libgmp memory functions. This is considered a bug and should be >> + fixed starting v3.0.6. >> + Before gdb commit 880ae75a2b7 "gdb delay guile initialization until >> + gdbscm_finish_initialization", that bug had no effect for gdb, >> + because gdb subsequently called mp_get_memory_functions to install >> + its own custom functions in _initialize_gmp_utils. However, since >> + aforementioned gdb commit the initialization order is reversed, >> + allowing libguile to install a custom malloc that is incompatible >> + with the custom free as used in gmp-utils.c, resulting in a >> + "double free or corruption (out)" error. >> + Work around the libguile bug by saving the libgmp memory functions >> + before guile initialization, and restoring them afterwards. */ >> + void *(*alloc_func) (size_t); >> + void *(*realloc_func) (void *, size_t, size_t); >> + void (*free_func) (void *, size_t); >> + mp_get_memory_functions (&alloc_func, &realloc_func, &free_func); > > I think any time we do SAVE-VALUE -> WORK -> RESTORE-VALUE, we should > be wrapping this up in an RAII class. Right now I don't believe > scm_with_guile can throw an exception, but you never know how the code > will change in the future, and creating an RAII class now just makes > things future proof. > Yes, that makes sense, I've updated the patch. I'll commit like this unless you have further comments. Thanks, - Tom --------------19F87ED6182D75C9DCA2CBC3 Content-Type: text/x-patch; charset=UTF-8; name="0001-gdb-guile-Don-t-allow-libguile-to-change-libgmp-mem-fns.patch" Content-Transfer-Encoding: quoted-printable Content-Disposition: inline; filename*0="0001-gdb-guile-Don-t-allow-libguile-to-change-libgmp-mem-fns"; filename*1=".patch" [gdb/guile] Don't allow libguile to change libgmp mem fns Since gdb commit 880ae75a2b7 "gdb delay guile initialization until gdbscm_finish_initialization" I'm running into: =2E.. (gdb) print My_Var > 10.0^M free(): invalid pointer^M ERROR: GDB process no longer exists GDB process exited with wait status 5995 exp9 0 0 CHILDKILLED SIGABRT SIG= ABRT UNRESOLVED: gdb.ada/fixed_cmp.exp: gnat_encodings=3Dall: print My_Var > 1= 0.0 =2E.. The problem is that both gdb and libguile try to set the libgmp memory fu= nctions, and since the gdb commit the ones from libguile are effective, which resu= lts in gdb freeing some memory in a way that is not compatible with the way t= hat memory was actually allocated. The fact that libguile tries to set the libgmp memory functions is a bug = which should be fixed starting version v3.0.6. Meanwhile, work around this in gdb by not allowing libguile to set the li= bgomp memory functions. Tested on x86_64-linux. gdb/ChangeLog: 2021-05-03 Tom de Vries PR guile/27806 * guile/guile.c (struct scoped_restore_libgmp_memory_functions): New struct. (gdbscm_initialize): Use scoped_restore_libgmp_memory_functions to save and restore libgmp memory functions. --- gdb/guile/guile.c | 39 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) diff --git a/gdb/guile/guile.c b/gdb/guile/guile.c index bdf15cd498b..2d121b19505 100644 --- a/gdb/guile/guile.c +++ b/gdb/guile/guile.c @@ -637,6 +637,29 @@ call_initialize_gdb_module (void *data) return NULL; } =20 +/* RAII class used to restore libgmp memory functions. */ + +struct scoped_restore_libgmp_memory_functions +{ + scoped_restore_libgmp_memory_functions () + { + mp_get_memory_functions (&alloc_func, &realloc_func, &free_func); + } + + ~scoped_restore_libgmp_memory_functions () + { + mp_set_memory_functions (alloc_func, realloc_func, free_func); + } + + DISABLE_COPY_AND_ASSIGN (scoped_restore_libgmp_memory_functions); + +private: + /* The saved libgmp memory functions that need to be restored. */ + void *(*alloc_func) (size_t); + void *(*realloc_func) (void *, size_t, size_t); + void (*free_func) (void *, size_t); +}; + /* A callback to initialize Guile after gdb has finished all its initialization. This is the extension_language_ops.initialize "metho= d". */ =20 @@ -662,6 +685,22 @@ gdbscm_initialize (const struct extension_language_d= efn *extlang) { gdb::block_signals blocker; =20 + /* There are libguile versions (f.i. v3.0.5) that by default call + mp_get_memory_functions during initialization to install custom + libgmp memory functions. This is considered a bug and should be + fixed starting v3.0.6. + Before gdb commit 880ae75a2b7 "gdb delay guile initialization unt= il + gdbscm_finish_initialization", that bug had no effect for gdb, + because gdb subsequently called mp_get_memory_functions to instal= l + its own custom functions in _initialize_gmp_utils. However, sinc= e + aforementioned gdb commit the initialization order is reversed, + allowing libguile to install a custom malloc that is incompatible= + with the custom free as used in gmp-utils.c, resulting in a + "double free or corruption (out)" error. + Work around the libguile bug by saving the libgmp memory function= s + before guile initialization, and restoring them afterwards. */ + scoped_restore_libgmp_memory_functions restore_libgmp_memory_functio= ns; + /* scm_with_guile is the most portable way to initialize Guile. Plu= s we need to initialize the Guile support while in Guile mode (e.g.= , called from within a call to scm_with_guile). */ --------------19F87ED6182D75C9DCA2CBC3--