[Click] Recent optimizations may cause segmentation faults

[Eddie Kohler]

Hi Jimmy,

Thanks for this bug report. I will shortly set up a FreeBSD VM to
test, but do the latest commits work for you?

Eddie


On Thu, Aug 16, 2012 at 5:55 AM, Jimmy Kjällman
<jimmy.kjallman at nomadiclab.com> wrote:
> FYI,
>
> it seems that recent string-related optimizations in Click cause some problems when the code is compiled with GCC 4.2.1 - which is a rather old compiler, but is still used as the default compiler in some systems (e.g. in FreeBSD 8 and 9). Of course, some other versions of GCC might also have the same problem.
>
> The code gets compiled (without errors etc.), but segmentation faults may occur when Click is started.
>
> With other, newer compilers that I tried (e.g. GCC 4.6), the code seems to work as it should.
>
>
> Some more details:
>
> It seems that commit "String, StringAccum: Call strlen() early when the result's a constant" (8b94ae6) causes problems for GCC 4.2.1, at least based on my observations on FreeBSD and Mac OS X.
>
> E.g. in String::String(const char *cstr), the code based on __builtin_constant_p(strlen(cstr)) and inlining doesn't get compiled correctly for some reason, so assign(cstr, strlen(cstr), false) gets called instead of assign(cstr, -1, false) at runtime. Possibly this is what always happens. If then cstr is NULL (for example), calling strlen(NULL) obviously causes a segmentation fault.
>
> This error is very easy to produce: Running "click" without any arguments results in a segmentation fault in the string constructor. This happens before starting to read a configuration from stdin. Apparently this error also occurs if a configuration file given as input starts with require(...), for instance.
>
> The current code works if I compile Click e.g. with GCC 4.6 in FreeBSD or LLVM-GCC 4.2.1 in OS X - and that's OK for me. Possibly some other workarounds, such as giving suitable options to the old compiler, might also work - but I haven't tried any. And I'm not sure whether this error occurs on all platforms.
>
>
>  - Jimmy
>
>
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