From: Bernd Edlinger <bernd.edlinger@hotmail.de>
To: Jeff Law <law@redhat.com>, Martin Sebor <msebor@gmail.com>,
Gcc Patch List <gcc-patches@gcc.gnu.org>
Subject: Re: PING [PATCH] warn for strlen of arrays with missing nul (PR 86552, 86711, 86714) )
Date: Sat, 25 Aug 2018 06:32:00 -0000 [thread overview]
Message-ID: <AM5PR0701MB2657E36E54AB1B39064A58B3E4350@AM5PR0701MB2657.eurprd07.prod.outlook.com> (raw)
In-Reply-To: <e2cfaf66-53e0-eac7-e78d-eb4311db56bc@redhat.com>
On 08/25/18 01:54, Jeff Law wrote:
> On 08/24/2018 11:26 AM, Bernd Edlinger wrote:
>> On 08/24/18 18:51, Jeff Law wrote:
>>>> Well, this is broken for wide character strings.
>>>> but I hope we can get rid of STRING_CST which are
>>>> not explicitly null terminated.
>>
>> I am afraid that is not going to happen.
>> Maybe we can get STRING_CST that are never longer
>> than the TYPE_UNIT_SIZE, but c_strlen and c_getstr
>> need to take care that the string is zero-terminated.
>>
>> string_constant, should not promise the string is zero terminated.
>> But instead it can promise that:
>> 1) the STRING_CST is valid up to TREE_STRING_LENGTH
>> 2) mem_size is >= TREE_STRING_LENGTH
>> 3) memory between TREE_STRING_LENGTH and mem_size is ZERO.
>>
>> It will not guarantee anything about zero termination any more.
> Interesting because those conditions would be sufficient to deal with a
> regression I stumbled over after fixing Martin's patch to not assume
> that all STRING_CSTs are NUL terminated.
>
> But I need to think about this a bit more. Essentially the question
> we'd need to ask is whether or not these are sufficient in general or
> just in specific cases.
>
> I tend to think they're not sufficient in general. If a string returned
> by string_constant that didn't have a terminating NUL, but which did
> pass the tests above were ultimately passed to the runtime's str*
> routines, then the call may run off the end of the string. We'd like to
> be able to warn for that.
>
> So ISTM those rules are only valid in contexts where we know the result
> isn't going to be passed to str* and friends within the C library.
>
> I do think they're sufficient to avoid problems with the
> tree-ssa-forwprop code we've looked at. So what may make the most sense
> is to have that routine indicate it's willing to accept unterminated
> strings, then check the conditions above before optimizing the code.
>
There are not too many callers of string_constant.
Not all need zero termination.
But I think if the are interested in zero-termination
they should simply call c_strlen or c_getstr.
>>
>> In the end, the best approach might be to either merge my patch
>> with Martins, or step-wise, first fixing wrong code, and then
>> implementing warnings without fixing wrong code.
> Unsure at this time. I've been working with both. I suspect that if we
> went with yours that we'd then turn around and layer Martin's on top of
> it because of the desire to signal to callers that we have an
> unterminated string and have the callers take appropriate action. Which
> begs the question of whether or not we just go with Martin's -- ie, is
> there really any value in using both. I haven't seen indications there
> is value in that approach, but I'm still poking at things.
>
Well, ya call it "layer one patch over the other"
I call it "incremental improvements".
Bernd.
next prev parent reply other threads:[~2018-08-25 6:32 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-19 20:09 [PATCH] warn for strlen of arrays with missing nul (PR 86552) Martin Sebor
2018-07-25 23:38 ` PING " Martin Sebor
2018-07-30 19:18 ` Martin Sebor
2018-08-02 2:44 ` PING [PATCH] warn for strlen of arrays with missing nul (PR 86552, 86711, 86714) ) Martin Sebor
2018-08-02 13:26 ` Bernd Edlinger
2018-08-02 18:56 ` Bernd Edlinger
2018-08-02 20:34 ` Martin Sebor
2018-08-03 13:01 ` Bernd Edlinger
2018-08-03 19:59 ` Martin Sebor
2018-08-15 5:31 ` Jeff Law
2018-08-29 17:17 ` Jeff Law
2018-08-24 6:36 ` Jeff Law
2018-08-24 12:28 ` Bernd Edlinger
2018-08-24 16:04 ` Jeff Law
2018-08-24 21:56 ` Bernd Edlinger
2018-08-24 16:51 ` Jeff Law
2018-08-24 17:26 ` Bernd Edlinger
2018-08-24 23:54 ` Jeff Law
2018-08-25 6:32 ` Bernd Edlinger [this message]
2018-08-25 17:33 ` Jeff Law
2018-08-25 18:36 ` Bernd Edlinger
2018-08-25 19:02 ` Jeff Law
2018-08-25 19:32 ` Bernd Edlinger
2018-08-25 20:42 ` Martin Sebor
2018-08-26 10:20 ` Bernd Edlinger
2018-08-25 23:22 ` Jeff Law
2018-08-17 5:15 ` Jeff Law
2018-08-17 14:38 ` Martin Sebor
2018-08-13 21:23 ` [PATCH 0/6] improve handling of char arrays with missing nul (PR 86552, 86711, 86714) Martin Sebor
2018-08-13 21:25 ` [PATCH 1/6] prevent folding of unterminated const arrays in memchr calls (PR " Martin Sebor
2018-08-13 21:27 ` [PATCH 3/6] detect unterminated const arrays in strcpy calls (PR 86552) Martin Sebor
2018-08-30 22:31 ` Jeff Law
2018-08-13 21:28 ` [PATCH 4/6] detect unterminated const arrays in sprintf " Martin Sebor
2018-08-30 22:55 ` Jeff Law
2018-08-13 21:29 ` [PATCH 6/6] detect unterminated const arrays in strnlen " Martin Sebor
2018-08-30 23:25 ` Jeff Law
2018-10-01 21:49 ` Jeff Law
2018-08-13 21:29 ` [PATCH 5/6] detect unterminated const arrays in stpcpy " Martin Sebor
2018-08-30 23:07 ` Jeff Law
2018-09-14 18:39 ` Jeff Law
2018-08-14 3:21 ` [PATCH 2/6] detect unterminated const arrays in strlen " Martin Sebor
2018-08-30 22:15 ` Jeff Law
2018-08-31 2:25 ` Martin Sebor
2018-08-15 6:02 ` [PATCH 0/6] improve handling of char arrays with missing nul (PR 86552, 86711, 86714) Jeff Law
2018-08-15 14:47 ` Martin Sebor
2018-08-15 15:42 ` Jeff Law
2018-08-24 10:13 ` Richard Biener
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