RFR: JDK-8256864: [windows] Improve tracing for mapping errors [v4]

[Ioi Lam]

On Tue, 1 Dec 2020 11:16:17 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> To analyze JDK-8256729 further, we need more tracing:
>> 
>> 1) We should print all mappings inside the split area if os::split_reserved_memory() fails
>> 
>> 2) The print-mapping code on windows has some shortcomings:
>> - should not probe for mappings outside of what we know are valid address ranges for Windows
>> - should handle wrap-arounds - it should be possible to print the whole address space
>> - Protection information is printed wrong (MEMORY_BASIC_INFORMATION.Protect would be the correct member)
>> - should be printed in a more compact manner - base address should be on the same line as the first region
>> - maybe adorned with some basic range info, e.g. library mappings
>
> Thomas Stuefe has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:
> 
>  - Print a short snippet for unknown mappings
>  - Merge
>  - Fix gtest for MacOS and AIX
>  - Merge
>  - Initial patch

Marked as reviewed by iklam (Reviewer).

src/hotspot/os/windows/os_windows.cpp line 6002:

> 6000:   for (int i = 0; i < num_words; i++) {
> 6001:     v[i] = SafeFetch32((int*)p + i, errval);
> 6002:     if (v[i] == errval) {

How about
if (SafeFetch32((int*)p + i, 0x1234) == 0x1234 && 
    SafeFetch32((int*)p + i, 0x5678) == 0x5678) {
  return;
} else {
  v[i] = SafeFetch32((int*)p + i, 0);
}

-------------

PR: https://git.openjdk.java.net/jdk/pull/1390