[cfe-dev] Why clang needs to fork into itself?

Ted Kremenek kremenek at apple.com
Tue Jan 28 16:55:19 PST 2014

On Jan 28, 2014, at 4:35 PM, Alp Toker <alp at nuanti.com> wrote:

> On 28/01/2014 22:20, Ted Kremenek wrote:
>> On Jan 28, 2014, at 2:16 PM, Yuri <yuri at rawbw.com> wrote:
>>> On 01/28/2014 14:10, Ted Kremenek wrote:
>>>> The few million users of Clang that I deal with never invoke the compiler directly from the command line.  Most of them probably don’t know how to.  The use the compiler from an IDE. That can, however, look at a build log and see that a crash report was generated for them, including a shell script that can be provided in a bug report that reruns the compiler with the correct arguments to reproduce the crash.
>>> If they don't know how to run a compiler, how can they possibly know know to program anything? Programming is much more complicated and involved than simply running a compiler. And you are saying there are millions of them?
>>> Yuri
>> For them they know enough to run the compiler.  They can simply click “Build” in an IDE.  Sure they need to understand the compilation model, as implied by the programming language, but they don’t need to memorize all the list of flags, etc., that are needed to run the compiler from the command line. I’m not saying that everyone doesn’t know how to use the compiler directly from the command line, but I’d argue that a very large constituency of developers (who clearly have demonstrated that they can write software) don’t have this knowledge, nor do they need it.
> Yuri, Ted,
> This is an open-ended argument and I think in this case you're *both* right. It is a handy default to enable a reproducible shell script and we certainly want to preserve those.
> The community is however interested in finding lighter ways to achieve that with a single process, whether it's Breakpad or something built upon the existing crash handler facilities in LLVM.
> The ability to disable and debug directly would be useful in some cases and "copy and paste the -cc1 invocation" isn't ideal so on that part I agree with Yuri.
> Alp.

I’m not married to forking clang.  I just don’t think we should regress on this functionality, even temporarily.  It is extremely important to us, far more than being able to debug clang directly without pasting the -cc1 invocation.  For the latter, in my experience one quickly learns what to do if you are hacking on clang.  I won’t argue that it is great, but it’s trivial to do when you compare it against losing good signal from bug reports.

If another solution is available other than forking that accomplishes the same aim with capturing reproducible failure cases, then I think we should adopt that first before dropping forking.  Alternatively, if we preserve the forking behavior, possibly as being conditionally compiled, that’s fine with me.  Within Apple we’ll just continue to build it that way.
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