RFR: 8330539: Use #include <alloca.h> instead of -Dalloca'(size)'=__builtin_alloca'(size)' for AIX

[Julian Waters]

On Thu, 2 May 2024 09:54:14 GMT, Joachim Kern <jkern at openjdk.org> wrote:

> We need to find a better way to handle alloca on AIX.
> 
> See the discussion in the PR for https://bugs.openjdk.org/browse/JDK-8329257, e.g. https://github.com/openjdk/jdk/pull/18536#discussion_r1568650313 in which three alternatives are suggested. Quoting:
> 
> Let me summarize the choices we have and ask for your vote.
> Magnus dislikes the -Dalloca'(size)'=__builtin_alloca'(size)' in flags-cflags.m4 I introduced to get rid of
> 
> #if defined(_AIX)
> #include <alloca.h>
> #endif
> 
> in globalDefinitions_gcc.hpp.
> 
> We have four possible solutions
> 
> 1. Reintroduce
> 
> #if defined(_AIX)
> #include <alloca.h>
> #endif
> 
> in globalDefinitions_gcc.hpp.
> 
> 2. Unconditionally introduce only #include <alloca.h> in globalDefinitions_gcc.hpp. This should work for all platforms using this header including the unofficial Windows/gcc Port, although only AIX needs it.
> 
> 3. Add
> 
> #if defined(_AIX)
> #include <alloca.h>
> #endif
> 
> to the sources using alloca(). These are
> /hotspot/share/runtime/os.cpp
> /hotspot/share/runtime/javaThread.cpp
> /hotspot/share/utilities/vmError.cpp
> Here we need the AIX condition, because otherwise the classic Windows Build (NTAMD64) fails.
> 
> 4. Replace -Dalloca'(size)'=__builtin_alloca'(size)' in flags-cflags.m4 by -U__STRICT_ANSI__ at the same place. Explanation can also found in https://github.com/openjdk/jdk/pull/18536#discussion_r1583360569 and following.
> 
> I will implement the solution with the most likes and having no dislike.

I stand corrected, it seems that MinGW distributions don't have alloca.h in their headers. No worries, the Windows/gcc Port will handle this downstream

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PR Comment: https://git.openjdk.org/jdk/pull/19053#issuecomment-2091958780