RFR: 8348286: [AIX] clang 17 introduces new warning Wtentative-Definitions which produces Build errors [v3]

[Magnus Ihse Bursie]

On Thu, 23 Jan 2025 13:48:06 GMT, Joachim Kern <jkern at openjdk.org> wrote:

>> We (SAP) try to introduce the ‘IBM Open XL C/C++ for AIX 17.1.2’ (based on clang 17) as a feasible compiler for jdk25, because in combination with the 17.1.3 runtime this would enable the support for ubsan.
>> Unfortunately, the new compiler comes along with a new set of compiler warnings turned into errors by -Werror.
>> One of the warnings is -Wtentative-definitions. It is fired when a variable definition in a header is found:
>> /jdk/src/java.desktop/share/native/libawt/awt/image/imageInitIDs.h:36:20: error: possible missing 'extern' on global variable definition in header [-Werror,-Wtentative-definitions]
>>    36 | IMGEXTERN jfieldID g_BImgRasterID;
>>       | ^
>> From now on headers allow only extern declarations of variables. The definition must take place in a c/cpp file. This means e.g.
>> imageInitIDs.h:36:20
>>    36 extern jfieldID g_BImgRasterID;
>> and the corresponding c-File
>>    jfieldID g_BImgRasterID;
>> 
>> The other possible solution would be to compile everything with
>> -Wno-tentative-definitions
>> which could be set in flags-cflags.m4, if compiling with clang 17.
>
> Joachim Kern has updated the pull request incrementally with one additional commit since the last revision:
> 
>   remove old solution

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Marked as reviewed by ihse (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/23236#pullrequestreview-2570094539