RFR: 8273152: Refactor CDS FileMapHeader loading code [v5]

[Yumin Qi]

On Wed, 6 Oct 2021 04:15:06 GMT, Ioi Lam <iklam at openjdk.org> wrote:

>> Yumin Qi has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Added a helper class to facilitate checking archive
>
> src/hotspot/share/cds/filemap.cpp line 1205:
> 
>> 1203:   }
>> 1204: 
>> 1205:   _header = (FileMapHeader*)os::malloc(gen_header->_header_size, mtInternal);
> 
> There's no need to allocate and read the header again. It's already in gen_header. This should be enough:
> 
> 
> _header = (FileMapHeader*)gen_header;

see above reply. We need read the full _header_size for _header. Also note that helper class will delete gen_header when out of scope.

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PR: https://git.openjdk.java.net/jdk/pull/5768