From 585a756a75886bcb198fe8a641886a38540cfc9f Mon Sep 17 00:00:00 2001 From: Tomi Ollila Date: Thu, 29 Nov 2012 16:23:09 +0200 Subject: [PATCH] Re: [PATCH] lib: fix warnings when building with clang --- da/a4013fc84c8e93115e05b9b3fbd1acdb79a702 | 168 ++++++++++++++++++++++ 1 file changed, 168 insertions(+) create mode 100644 da/a4013fc84c8e93115e05b9b3fbd1acdb79a702 diff --git a/da/a4013fc84c8e93115e05b9b3fbd1acdb79a702 b/da/a4013fc84c8e93115e05b9b3fbd1acdb79a702 new file mode 100644 index 000000000..c34877a36 --- /dev/null +++ b/da/a4013fc84c8e93115e05b9b3fbd1acdb79a702 @@ -0,0 +1,168 @@ +Return-Path: +X-Original-To: notmuch@notmuchmail.org +Delivered-To: notmuch@notmuchmail.org +Received: from localhost (localhost [127.0.0.1]) + by olra.theworths.org (Postfix) with ESMTP id 63D10431FAF + for ; Thu, 29 Nov 2012 06:23:13 -0800 (PST) +X-Virus-Scanned: Debian amavisd-new at olra.theworths.org +X-Spam-Flag: NO +X-Spam-Score: 0 +X-Spam-Level: +X-Spam-Status: No, score=0 tagged_above=-999 required=5 tests=[none] + autolearn=disabled +Received: from olra.theworths.org ([127.0.0.1]) + by localhost (olra.theworths.org [127.0.0.1]) (amavisd-new, port 10024) + with ESMTP id ox3NmJXXXAbj for ; + Thu, 29 Nov 2012 06:23:12 -0800 (PST) +Received: from guru.guru-group.fi (guru.guru-group.fi [46.183.73.34]) + by olra.theworths.org (Postfix) with ESMTP id 26627431FAE + for ; Thu, 29 Nov 2012 06:23:12 -0800 (PST) +Received: from guru.guru-group.fi (localhost [IPv6:::1]) + by guru.guru-group.fi (Postfix) with ESMTP id 78A681000E5; + Thu, 29 Nov 2012 16:23:09 +0200 (EET) +From: Tomi Ollila +To: Jani Nikula , + Ethan Glasser-Camp , notmuch@notmuchmail.org +Subject: Re: [PATCH] lib: fix warnings when building with clang +In-Reply-To: +References: <1349076971-2065-1-git-send-email-jani@nikula.org> + <87pq4c61hc.fsf@betacantrips.com> <87vce3vf5q.fsf@nikula.org> + +User-Agent: Notmuch/0.14+116~g29fcdb5 (http://notmuchmail.org) Emacs/24.2.1 + (x86_64-unknown-linux-gnu) +X-Face: HhBM'cA~ +MIME-Version: 1.0 +Content-Type: text/plain +X-BeenThere: notmuch@notmuchmail.org +X-Mailman-Version: 2.1.13 +Precedence: list +List-Id: "Use and development of the notmuch mail system." + +List-Unsubscribe: , + +List-Archive: +List-Post: +List-Help: +List-Subscribe: , + +X-List-Received-Date: Thu, 29 Nov 2012 14:23:13 -0000 + +On Mon, Oct 22 2012, Tomi Ollila wrote: + +> On Sun, Oct 21 2012, Jani Nikula wrote: +> +>> On Sun, 21 Oct 2012, Ethan Glasser-Camp wrote: +>>> Jani Nikula writes: +>>> +>>>> Building notmuch with CC=clang and CXX=clang++ produces the warnings: +>>>> +>>>> CC -O2 lib/tags.o +>>>> lib/tags.c:43:5: warning: expression result unused [-Wunused-value] +>>>> talloc_steal (tags, list); +>>>> ^~~~~~~~~~~~~~~~~~~~~~~~~ +>>>> /usr/include/talloc.h:345:143: note: expanded from: +>>>> ...__location__); __talloc_steal_ret; }) +>>>> ^~~~~~~~~~~~~~~~~~ +>>>> 1 warning generated. +>>>> +>>>> CXX -O2 lib/message.o +>>>> lib/message.cc:791:5: warning: expression result unused [-Wunused-value] +>>>> talloc_reference (message, message->tag_list); +>>>> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +>>>> /usr/include/talloc.h:932:36: note: expanded from: +>>>> ...(_TALLOC_TYPEOF(ptr))_talloc_reference_loc((ctx),(ptr), __location__) +>>>> ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +>>>> 1 warning generated. +>>>> +>>>> Check talloc_reference() return value, and explicitly ignore +>>>> talloc_steal() return value as it has no failure modes, to silence the +>>>> warnings. +>>>> --- +>>>> lib/message.cc | 4 +++- +>>>> lib/tags.c | 2 +- +>>>> 2 files changed, 4 insertions(+), 2 deletions(-) +>>>> +>>>> diff --git a/lib/message.cc b/lib/message.cc +>>>> index 978de06..320901f 100644 +>>>> --- a/lib/message.cc +>>>> +++ b/lib/message.cc +>>>> @@ -788,7 +788,9 @@ notmuch_message_get_tags (notmuch_message_t *message) +>>>> * possible to modify the message tags (which talloc_unlink's the +>>>> * current list from the message) while still iterating because +>>>> * the iterator will keep the current list alive. */ +>>>> - talloc_reference (message, message->tag_list); +>>>> + if (!talloc_reference (message, message->tag_list)) +>>>> + return NULL; +>>>> + +>>>> return tags; +>>>> } +>>> +>>> Hi! What you did with talloc_steal is obviously fine. +>>> +>>> I'd be happier about what you did with talloc_reference() if there were +>>> precedent, or a clearly-articulated convention for notmuch. Instead this +>>> is the third use in the codebase that I can see, and the other two are +>>> each unique to themselves. In mime-node.c we print an "out-of-memory" +>>> error and in lib/filenames.c we cast (void) talloc_reference (...), I +>>> guess figuring that we're pretty much hosed anyhow if we run out of +>>> memory. +>>> +>>> Why return NULL here? It seems like if talloc_reference fails, we're +>>> going to crash eventually, so we should print an error to explain our +>>> impending doom. I'd guess you're uneasy printing anything from lib/, but +>>> still want to signal an error, and the only way you can do so is to +>>> return NULL. I guess that silences the compiler warning, but it's not +>>> really the correct way to handle the error IMO. On the other hand, it's +>>> such a weird corner case that I don't even think it merits a FIXME +>>> comment. +>>> +>>> How about an assert instead of a return NULL? +>> +>> No. I don't think a library should assert, exit, or print to stderr on +>> this sort of thing. It's up to the calling application. Even if it +>> probably doesn't have many choices left, given how much memory +>> talloc_reference needs (not much). +>> +>> Ignoring the talloc_reference return value with (void) is just wrong, +>> and the caller of notmuch_message_get_tags should anticipate a NULL +>> return. So IMHO that's the pragmatic thing to do in this mostly +>> theoretical situation, the biggest change being silencing the warning. +> +> I agree that the best library can do is to return NULL (if talloc had +> a place in ctx to store error indication that could be used but I did +> not see any in quick look -- and using global there is not a good idea) +> +> but, before returning NULL should 'tags' be freed. + +Ah, this is talloc() stuff, so the patch is good in this part. + +> Additionally, should lib/filenames.c be changed to have code: +> +> if (unlikely (talloc_reference(filenames, list) == NULL)) { +> talloc_free (filenames); +> return NULL; +> } + +More like + +if (unlikely (talloc_reference(filenames, list) == NULL)) + return NULL; + +But that is out of scope of this patch... + + +so, +1 + +Tomi + +>> BR, +>> Jani. +> +> (btw, what are the chances that program crashes before returning NULL +> due to page fault in stack frame allocation ???) +> +> Tomi -- 2.26.2