Request or comment: 8071690: Include local HotSpot headers before the system headers

[Lindenmaier, Goetz]

Hi David,

but by enforcing that rule, the effect is limited to the header
that includes other system headers.  You can fix the problem
by adding globalDefinitions.hpp in that one header foo.h, and whoever
includes foo.h get's it right.

If fcntl.h had been added to foo.h in first place, all files that include
foo.h must include globalDefinitions.hpp before it ... not very easy to 
catch.

Best regards,
   Goetz.





-----Original Message-----
From: hotspot-dev [mailto:hotspot-dev-bounces at openjdk.java.net] On Behalf Of David Holmes
Sent: Wednesday, January 28, 2015 5:22 AM
To: Volker Simonis; HotSpot Open Source Developers
Subject: Re: Request or comment: 8071690: Include local HotSpot headers before the system headers

Hi Volker,

On 28/01/2015 3:29 AM, Volker Simonis wrote:
> Hi,
>
> I've just opened "8071690: Include local HotSpot headers before the
> system headers" but before I start working on it I'd like to hear what
> others think about the problem. If there's a consensus that it will be
> worth while doing this change I'll be happy to start working on it.

As I wrote in the bug report:

I don't see how you can apply this as a general rule - or at least not 
without some further rules. If local foo.h depends on a system header 
then it will #include it, so a file that #includes foo.h can't control 
the order of that system header include.

We need to recognize (and detect!) where we have implicit ordering 
constraints but I don't think a general rule actually helps with that. 
And there may be cases where we rely on a system include coming first eg:

#ifndef SOME_SYSTEM_THING
   #define SOME_SYSTEM_THING xxx
#endif

David
-----

> https://bugs.openjdk.java.net/browse/JDK-8071690
>
> The following description is copied from the bug report for your convenience:
>
> There's no general rule in which order header files should be included
> but I think a good hint is to include local, project specific headers
> before system headers. This is mainly for two reasons:
>
> 1. It prevents that dependencies from local header files to system
> headers are hidden because a local header is included after a system
> header by chance. Instead, every local header should explicitly
> specify the system headers it depends on.
>
> 2. It enables the definition of local macros which control the
> behaviour of the system headers which are included later on.
>
> Point two may be considered bad style, but we actually use it for
> example in src/share/vm/utilities/globalDefinitions.hpp where we
> define "__STDC_FORMAT_MACROS" before we include "<inttypes.h>" in the
> compiler specific global definitions file.
>
> "__STDC_FORMAT_MACROS" controls the definition of the printf format
> macros in "<inttypes.h>" but this can only work if "<inttypes.h>" is
> really included AFTER the definition of "__STDC_FORMAT_MACROS". And
> this can only wok if every file includes the local HotSpot headers
> before any system headers, because otherwise "<inttypes.h>" may be
> indirectly included by a system header before we had a chance to
> define "__STDC_FORMAT_MACROS".
>
> This is exactly what happened after the integration of 8050807 which
> added the system include "<fcntl.h>" to vmError.cpp as follows:
>
> #include <fcntl.h>
> #include "precompiled.hpp"
> #include "code/codeCache.hpp"
>
> This change broke the build on AIX because "<fcntl.h>" indirectly
> included "<inttypes.h>" BEFORE we defined "__STDC_FORMAT_MACROS".
>
> To prevent such errors in the future I propose to change all HotSpot
> source files to always include the system headers AFTER the inclusion
> of the project specific HotSpot headers.
>
> I’ve attached a small Pythin script to this bug report which can be
> used as follows to detect the files which are currently violating this
> rule:
>
> find src/ \( -name "*.cpp" -o -name "*.hpp" \) -type f -exec python
> include.py {} \;
>
> src/os/solaris/dtrace/generateJvmOffsets.cpp: system header #include
> <proc_service.h> included before local header #include
> "code/codeBlob.hpp"
> src/os/windows/vm/decoder_windows.hpp: system header #include
> <imagehlp.h> included before local header #include
> "utilities/decoder.hpp"
> src/os_cpu/bsd_zero/vm/os_bsd_zero.cpp: system header # include
> <pthread_np.h> included before local header #include
> "assembler_zero.inline.hpp"
> src/share/vm/adlc/adlc.hpp: system header #include <iostream> included
> before local header #include "string.h"
> src/share/vm/libadt/port.hpp: system header #include <string.h>
> included before local header #include "port_tandem.hpp"
> src/share/vm/runtime/os.hpp: system header # include <setjmp.h>
> included before local header # include "jvm_solaris.h"
> src/share/vm/trace/traceDataTypes.hpp: system header #include
> <stddef.h> included before local header #include
> "utilities/globalDefinitions.hpp"
> src/share/vm/utilities/dtrace.hpp: system header #include
> <sys/types.h> included before local header #include
> "dtracefiles/hotspot.h"
> src/share/vm/utilities/elfFile.cpp: system header #include <new>
> included before local header #include "memory/allocation.inline.hpp"
> src/share/vm/utilities/elfFile.hpp: system header #include <stdio.h>
> included before local header #include "globalDefinitions.hpp"
> src/share/vm/utilities/vmError.cpp: system header #include <fcntl.h>
> included before local header #include "precompiled.hpp"
>
> The script is written in Python intentionally such that it can be
> easily added as an automated hook to jcheck to prevent violations of
> this inclusion rule in the future.
>
> Of course we can also try to not rely on the inclusion order at all.
> IMHO it actually seems that this is the cleanest solution, but it may
> require moving some macro definitions from header files right into the
> command line (e.g. -D__STDC_FORMAT_MACROS for the example above). By
> the way, that's actually the way how I've fixed the above mentioned
> compile error on AIX without the need to touch any shared files.
>
> What do you think?
>
> Regards,
> Volker
>