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Date: Thu, 23 Apr 2015 06:08:27 +0100
From: Raphael Cohn <raphael.cohn@...rmmq.com>
To: musl@...ts.openwall.com
Subject: Re: setenv if value=NULL, what say standard? Bug?
Fail fast, fail early is always the right thing to do. I've seen far too
much code in my career that tries to 'carry on' after encountering an
unexpected condition. It's always the wrong thing to do, even for nuclear
power plants. Once you're in UB land, the rest of your reasoning about your
code is invalid. The best you can do is gracefully shutdown and capture as
much diagnostic info as is feasible. Expecting musl to 'cover up' should be
seen the same as in the real world - cover ups just make the problem worse.
Unexpected is not the same as expected but unpleasant to deal with eg
failures to open(). And so hence the arguments about checked and unchecked
exceptions and so on.
Oh and auto restarting daemons is almost always wrong. For exactly the same
reasoning - and frequently leads to data corruption.
On 23 Apr 2015 05:25, "Jean-Marc Pigeon" <jmp@...e.ca> wrote:
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> On 04/22/2015 10:15 PM, Rich Felker wrote:
> > On Wed, Apr 22, 2015 at 09:26:57PM -0400, Jean-Marc Pigeon wrote:
> >>> I think the only safe conclusion is that the application is
> >>> incorrect and should ensure that setenv() is never called with
> >>> a NULL value.
> >>>
> >> Checked glibc, My understanding, it set something as "name=" in
> >> the environment, so the variable is present but value is "empty"i
> >> (top application to decide what to do). uclibc does something
> >> similar (as far I can tell looking at source code)..
> >>
> >>
> >> The application is not careful enough, but not incorrect as
> >> such.
> >
> > It's definitely incorrect. It's doing something that invokes
> > undefined behavior.
> >
> >> Note: we may have tons of applications with the same problem. if
> >> we keep musl setenv like that, musl will be seen as quite
> >> unreliable.
> >
> > No, actually glibc is fixing this bug (maybe they already did).
> > See the thread beginning here:
> >
> > https://sourceware.org/ml/libc-alpha/2015-03/threads.html#00449
> >
> > My understanding is that glibc is planning to do, or already does
> > in the latest version, exactly what musl is doing.
> >
> >> If this situation is indeed UB, there is 2 options for musl: 1)
> >> Swallow the problem nicely... as glibc and uclibc does. 2) Report
> >> an error.. EINVAL? (and document it in manual)
> >>
> >> Crashing at "libc" level is not an option.
> >
> > I can see how it might seem like that at first, but crashing is
> > actually the best possible behavior. Options 1 and 2 cover up a
> I strongly disagree, crashing is not an option for a tools as
> musl/libc.
>
> Think about this, you write an application working perfectly right,
> but 1 in 1000000 you reach something not trapped by low level and
> once in while the application (in production for month) just stop
> to work because "unexpected" within musl...
> (so someone will propose to set a cron to automatically restart this
> unreliable daemon, hmmm...)
>
> Far better to return "trouble" status, then it is to the application
> to decide what must be done in context, as ignore, override, bypass,
> crash, etc.
>
> A sensible policy in case of UB would be for such low level code to
> swallow the problem, (protect the hardware and keep the program
> running as much as possible).
>
> > potentially serious bug -- it's not clear what the application was
> > trying to do, most likely nobody even thought about what they were
> > trying to do, and even if they did have something in mind it's not
> > reliable or portable. The glibc wiki has some text taken from text
> > I wrote on the topic (copied from a stack overflow answer I gave)
> > here:
>
> As reported, the crashing application is hwclock, (util-linux-2.26),
> this a kind of code in the field for a very very long time, so the
> library (glibc and old libc) used for linux over the years defined an
> expected behavior to this "UB".
> As other occurrence of this could be present too in other
> program/application, crashing would make a bench of applications
> to be running hazard (you can have all kind situation with
> env variables, near unpredictable).
>
> Something worry me in comments I have seen in the proposed URL,
> IMHO purpose of musl/glibc is not to "find bugs by crashing", its
> purpose is to be a code "clean, lean, reliable, predictable" (as said
> above, "Protect the hardware, report problem, lets the above layer
> application decide what to do in case of problem").
>
> Crashing is not an option for code pertaining to musl/libc layer.
>
> (:-} why bother to return an error, just crash for all
> problems in open, close, write, etc. just bringing the crashing
> concept to the extreme :-}).
>
>
>
> >
> > https://sourceware.org/glibc/wiki/Style_and_Conventions#Invalid_pointers
> >
> > Specifically it covers why returning an error is not a good idea.
> My experience (for a long time now) about writing complex daemon
> running for months/year, it is not that straightforward (may
> be for a simple application it is)
>
> >
> > Rich
> >
>
>
> - --
>
> A bientôt
> ===========================================================
> Jean-Marc Pigeon E-Mail: jmp@...e.ca
> SAFE Inc. Phone: (514) 493-4280
> Clement, 'a kiss solution' to get rid of SPAM (at last)
> Clement' Home base <"http://www.clement.safe.ca">
> ===========================================================
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