RFR: 8299329: Assertion failure with fastdebug build when trying to use CDS without classpath

[Ashutosh Mehra]

On Fri, 23 Dec 2022 18:12:38 GMT, Severin Gehwolf <sgehwolf at openjdk.org> wrote:

>> It appears longest_common_app_classpath_prefix_len() is not returning correct value when there is no file separator in the path being searched backwards. Instead of returning 0 it return 1.
>> 
>> In case of empty classpath, it can result in assertion failure in check_paths():
>> 
>> `assert(strlen(rp_array->at(i)) > (size_t)runtime_prefix_len, "sanity");`
>> 
>> It can also result in incorrectly validating the app classpaths if they only differ by first character. Eg:
>> 
>> Dump time:
>>   -cp hello.jar
>> Run time:
>>   -cp mello.jar
>> 
>> This would not result in classpath mismatch!
>> 
>> This fix updates longest_common_app_classpath_prefix_len() to return 0 if no file separator character is found.
>> 
>> Signed-off-by: Ashutosh Mehra <asmehra at redhat.com>
>
> Could we add a test for this a la `test/hotspot/jtreg/runtime/cds/appcds/WrongClasspath.java`?

@jerboaa I see WrongClasspath.java already has a test for "no classpath" condition, but it is not failing with debug build.
The command line used for running "no classpaht" test reveals it is actually running with a classpath:

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PR: https://git.openjdk.org/jdk/pull/11781