RFR: 8257913: Add more known library locations to simplify Linux cross-compilation [v3]

[Magnus Ihse Bursie]

On Mon, 8 Mar 2021 16:14:21 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> make/autoconf/platform.m4 line 364:
>> 
>>> 362:   AC_SUBST(OPENJDK_TARGET_CPU_AUTOCONF)
>>> 363:   AC_SUBST(OPENJDK_TARGET_LIBC)
>>> 364:   AC_SUBST(OPENJDK_TARGET_ABI)
>> 
>> I realize this has already been integrated, but I don't fully understand this. There is no corresponding change in spec.gmk.in adding OPENJDK_TARGET/BUILD_CPU_AUTOCONF and OPENJDK_TARGET/BUILD_ABI. 
>> 
>> So why the AC_SUBST()?
>
> I thought we need to declare these as `AC_SUBST` as we define the variables outside this file? I can revert these additions if you think these are incorrect.

No, they are only needed to be able to populate the @FOO@ tags in spec.gmk.in. All the *.m4 files are concatenated into a single shell script by autoconf, so referring to variables in a different m4 file does not really matter.

I don't think it's worth a separate bug to remove them, but if you touch the area again you can get rid of them while you're at it :)

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PR: https://git.openjdk.java.net/jdk/pull/2833