RFR: 8287001: Add warning message when fail to load hsdis libraries

[yuta]

On Thu, 19 May 2022 19:29:28 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> When failing to load hsdis(Hot Spot Disassembler) library (because there is no library or hsdis.so is old and so on),
>> there is no warning message (only can see info level messages if put -Xlog:os=info).
>> This should show a warning message to tell the user that you failed to load libraries for hsdis.
>> So I put a warning message to notify this.
>> 
>> e.g.
>> `
>
> Can you put the warning into `dll_load()`?
> We already print messages there with `-XX:+Vebose` (unfortunately it is available only in debug VM).
> Actually consider replacing print statements and `Verbose` check there with UL.

Hi @vnkozlov ,
I think if put warning into `Disassembler::dll_load()` , 
this would print duplicated error messages for each hsdis library as written in `Disassembler::load_library`.

  // Find the disassembler shared library.
  // Search for several paths derived from libjvm, in this order:
  // 1. <home>/lib/<vm>/libhsdis-<arch>.so  (for compatibility)
  // 2. <home>/lib/<vm>/hsdis-<arch>.so
  // 3. <home>/lib/hsdis-<arch>.so
  // 4. hsdis-<arch>.so  (using LD_LIBRARY_PATH)

Besides, message with `Verbose` check seems to check whether 
the length of the path of hsdis library is beyond the defined length ( not including the case of no library, or old version).

So, it seems reasonable to put the warning message into  `Disassembler::load_library` after finishing to check all patterns.

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PR: https://git.openjdk.java.net/jdk/pull/8782