PING: RFR: 8241439: jdk.NativeLibraryEvent hooks all opened regular files

[David Holmes]

Hi Yasumasa,

Not a review - sorry.

On 16/04/2020 10:30 am, Yasumasa Suenaga wrote:
> PING: Could you review it?
> 
>    JBS: https://bugs.openjdk.java.net/browse/JDK-8241439
>    webrev: http://cr.openjdk.java.net/~ysuenaga/JDK-8241439/webrev.01/
> 
> 
> Yasumasa
> 
> 
> On 2020/04/09 16:00, Yasumasa Suenaga wrote:
>> Hi all,
>>
>> Please review this change:
>>
>>    JBS: https://bugs.openjdk.java.net/browse/JDK-8241439
>>    webrev: http://cr.openjdk.java.net/~ysuenaga/JDK-8241439/webrev.00/
>>
>> HotSpot has os::get_loaded_modules_info() to get all loaded native 
>> libraries, however it would call callback in twice on same library on 
>> Linux. Also it would call callback even if the file is not a library.

I'm not at all sure I agree with the problem as presented. If I examine 
a mapfile I see for example:

7fb0400f0000-7fb0402b3000 r-xp 00000000 08:03 21081 
/usr/lib64/libc-2.17.so
7fb0402b3000-7fb0404b3000 ---p 001c3000 08:03 21081 
/usr/lib64/libc-2.17.so
7fb0404b3000-7fb0404b7000 r--p 001c3000 08:03 21081 
/usr/lib64/libc-2.17.so
7fb0404b7000-7fb0404b9000 rw-p 001c7000 08:03 21081 
/usr/lib64/libc-2.17.so

and I would expect to get the callback called for each of those lines 
because they report different mapped ranges. Is your approach 
consolidating this to a single callback with a contiguous range? Is that 
the kind of information people want to see? (I have no idea).

As for filtering out memory-mapped files like classes.jsa ... while it 
is not a library as such it may be useful information to present. So 
perhaps the filtering should be done in the client code rather than in 
the os::get_loaded_modules_info() code?

But this functionality was added purely for JFR so I think it is best if 
the JFR folk determine what is and isn't wanted here.

Thanks,
David
-----

>>
>> We can see this problem in jdk.NativeLibrary JFR event as below:
>>
>>
>> ```
>> jdk.NativeLibrary {
>>     startTime = 16:59:06.621
>>     name = "/usr/lib64/libc-2.30.so"
>>     baseAddress = 0x7FDB06ACC000
>>     topAddress = 0x7FDB06AF1000
>> }
>>
>> jdk.NativeLibrary {
>>     startTime = 16:59:06.621
>>     name = "/usr/lib64/libc-2.30.so"
>>     baseAddress = 0x7FDB06AF1000
>>     topAddress = 0x7FDB06C40000
>> }
>>
>>      :
>>
>> ```
>>
>> ```
>> jdk.NativeLibrary {
>>     startTime = 16:59:06.621
>>     name = 
>> "/home/ysuenaga/OpenJDK/jdk/build/linux-x86_64-server-fastdebug/images/jdk/lib/server/classes.jsa" 
>>
>>     baseAddress = 0x800000000
>>     topAddress = 0x800007000
>> }
>> ```
>>
>> This change uses dl_iterate_phdr() to get them, so these problem has 
>> gone.
>>
>>
>> Thanks,
>>
>> Yasumasa