RFR: build pragma error with gcc 4.4.7

[Kim Barrett]

> On Apr 21, 2018, at 11:18 AM, Andrew Hughes <gnu.andrew at redhat.com> wrote:
> 
> On 19 March 2018 at 23:23, Kim Barrett <kim.barrett at oracle.com> wrote:
>> There are also problems with the patch as provided.
>> 
>> (1) Since PRAGMA_DIAG_PUSH/POP do nothing in the version of gcc this
>> change is being made in support of, the warning would be disabled for
>> all following code in any translation unit that includes this file.
>> That doesn't seem good.
> 
> No, but it's really the only solution on those compilers. We have such
> usage already elsewhere e.g.
> 
> // Silence -Wformat-security warning for fatal()
> PRAGMA_DIAG_PUSH
> PRAGMA_FORMAT_NONLITERAL_IGNORED
>  fatal(buf);
> PRAGMA_DIAG_POP
>  return true; // silence compiler warnings
> }
> in src/hotspot/os_cpu/linux_zero/os_linux_zero.cpp
> 
> If there are other warnings, then they will picked up on newer compilers,
> especially when building with -Werror. I don't think it's likely people are
> doing development on older compilers, but rather that we have to use
> them to build for older platforms.

I would be a lot more comfortable if the possibly do-nothing push/pop and
the associated code were in a .cpp file, rather than in a .hpp file where it
could affect some open-ended and unexpected set of code.

But I think this is moot if os::readdir can be changed to call ::readdir rather
than ::readdir_r, as appears to be the case, possibly with some documentation
about not sharing the DIR* among multiple threads, at least not without locking.

That seemed to be what Michal was planning to do, but hasn’t gotten back to
it yet.