RFR (trivial): 8235819: -Wformat-overflow is reported from GCC 9

[Thomas Schatzl]

Hi,

On 15.12.19 07:08, Yasumasa Suenaga wrote:
> Hi Thomas, Leo,
> 
> How about this change?
> 
>    http://hg.openjdk.java.net/jdk/submit/rev/10816e67561a
> 
> It generates indent string via alloca().
> So get_indent() should be inlined.

(typical Hotspot style is without the "get_" prefix).

> 
> However it was failed at TestGCLogMessages on macOS only on submit repo 
> (mach5-one-ysuenaga-JDK-8235819-1-20191215-0359-7545712).
> 
> If you are generally ok to this change, could you share details of this 
> failure?
> I will fix it.

The alloca-allocated buffer will be freed at the exit of the 
get_indent() method, so the new code effectively accesses freed memory 
as get_indent() returns a pointer to it.

The intent of our comments has basically been:

- remove the "5" (or "4") in the Indents static.
- add a static indent() method that does something like:

static const char* indent(uint level) {
   assert(level < ARRAY_SIZE(Indents), "Too high indent level %u", level);
   return Indents[level];
}

And replace the direct access to the Indents array in the code with a 
call to  the indent() method.

If gcc still complains, add that additional indent level you added in 
webrev.00. I do not like easily avoidable pragmas in the code, and the 
additional level does not hurt, but others might disagree.

Probably also file a bug with gcc.

Thanks,
   Thomas