RFR: JDK-8329257: AIX: Switch HOTSPOT_TOOLCHAIN_TYPE from xlc to gcc [v3]

[Martin Doerr]

On Wed, 10 Apr 2024 09:40:16 GMT, Joachim Kern <jkern at openjdk.org> wrote:

>> Do we even need to include <alloca.h>? 
>> 
>> From the Linux man page for alloca:
>> 
>> By necessity, alloca() is a compiler built-in, also known as
>> __builtin_alloca().  By default, modern compilers automatically
>> translate all uses of alloca() into the built-in, but this is
>> forbidden if standards conformance is requested (-ansi, -std=c*),
>> in which case <alloca.h> is required, lest a symbol dependency be
>> emitted.
>> 
>> There are uses of it in shared code where there isn't an applicable include,
>> other than from globalDefinitions_xlc.hpp. So it appears all other supported
>> compilers do treat it as a built-in with the options we are providing, and
>> don't need the include. Maybe that's true for the new xlc compiler too?
>
> If I omit this #include <alloca.h>
> I get compiler errors of the following kind
> 
> .../src/hotspot/share/runtime/javaThread.cpp:2222:24: error: use of undeclared identifier 'alloca'
>     char* p1 = (char*) alloca(1);
>                        ^
> 
> 
> Of course I can do this include in every nagging file, but I thought it is simpler to keep it in the central header.

Is the comment in front of https://github.com/openjdk/jdk/blob/51ed69a586105b707ae616f9eba898449bf9fba7/src/hotspot/os/aix/os_aix.cpp#L28 still correct? Seems like it isn't followed everywhere.

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PR Review Comment: https://git.openjdk.org/jdk/pull/18536#discussion_r1559175426