RFR: 8286978: SIGBUS in libz during CDS initialization [v2]

[Calvin Cheung]

On Fri, 20 May 2022 14:48:36 GMT, Ioi Lam <iklam at openjdk.org> wrote:

>> test/lib/jdk/test/lib/cds/CDSArchiveUtils.java line 440:
>> 
>>> 438:             transferFrom(inputChannel, outputChannel, 0, offset);
>>> 439:             outputChannel.position(offset);
>>> 440:             outputChannel.write(ByteBuffer.wrap(bytes));
>> 
>> The changes for transferFrom looks good, but we still have a problem with outputChannel.write(), which can also return fewer bytes than requested (or even zero).
>> 
>> For simplicity, I think it's best to ditch FileChannel and use FileOutputStream.write() instead.
>
> Another option is to avoid using outputChannel.write(). Instead, duplicate some bytes from the end of the header.
> 
> 
>     public static File insertBytesRandomlyAfterHeader(File orgFile, String newFileName) throws Exception {
>         long headerSize = fileHeaderSize(orgFile);
>         long dupSize = getRandomBetween(0L, headerSize);
>         File dstFile = new File(newFileName);
>         try (FileChannel inputChannel = new FileInputStream(orgFile).getChannel();
>              FileChannel outputChannel = new FileOutputStream(dstFile).getChannel()) {
>             long orgSize = inputChannel.size();
>             // Copy the header
>             transferFrom(inputChannel, outputChannel, 0, headerSize);
>             // Copy dupSize bytes from the end of the header. Then, copy the rest
>             // of the input such that the new file will have the same size as
>             // the old file.
>             inputChannel.position(headerSize - dupSize);
>             transferFrom(inputChannel, outputChannel, headerSize, orgSize - headerSize);
>         }
>         return dstFile;
>     }

Thanks for the suggestions. I've pushed another commit with the above changes. I also changed the callsite in SharedArchiveConsistency.java since there's no need to pass in a byte array.

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PR: https://git.openjdk.java.net/jdk/pull/8799