RFR: 8275405: Linking error for classes with lambda template parameters and virtual functions [v2]

[Per Liden]

On Wed, 20 Oct 2021 12:23:28 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

>> We encountered the following linking error when trying to build Generational ZGC on Windows:
>> 
>> jvm.exp : error LNK2001: unresolved external symbol "const ZBasicOopIterateClosure<class <lambda_9767402e468f9fc654281195f9700e48> >::`vftable'" (??_7?$ZBasicOopIterateClosure at V<lambda_9767402e468f9fc654281195f9700e48>@@@@6B@)
>> 
>> 
>> I narrowed this down to a simple reproducer, which doesn't link when built through the HotSpot build system:
>> 
>> #include <functional>
>> std::function<void()> = [](){};
>> 
>> 
>> I found that we have a line in our make files that filters out symbols that contain the string vftable (though it checks the mangled name, so a bit hard to find):
>> 
>> else ifeq ($(call isTargetOs, windows), true)
>>   DUMP_SYMBOLS_CMD := $(DUMPBIN) -symbols *.obj
>>   FILTER_SYMBOLS_AWK_SCRIPT := \
>>       '{ \
>>         if ($$7 ~ /??_7.*@@6B@/ && $$7 !~ /type_info/) print $$7; \
>>       }'
>> 
>> 
>> The following line prints the vftable symbol if it doesn't contain the string 'type_info':
>>  if ($$7 ~ /??_7.*@@6B@/ && $$7 !~ /type_info/) print $$7;
>> 
>> The printed values are added to a list of symbols that get filtered out of the mapfile, which is then passed to the linker.
>> 
>> I can get the code to link if I add a second exception for vftable symbols containing the string 'lambda':
>>  if ($$7 ~ /??_7.*@@6B@/ && $$7 !~ /type_info/ && $$7 !~ /lambda/) print $$7;
>> 
>> I did an additional experiment where I completely removed this filtering of vftable symbols. When I did that the linker complained that we used more than 64K symbols.
>
> Stefan Karlsson has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix typo

Looks good to me!

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Marked as reviewed by pliden (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/6030