RFR: 8236569: -Xss not multiple of 4K does not work for the main thread on macOS [v5]

[Thomas Stuefe]

On Mon, 7 Jun 2021 03:18:32 GMT, Henry Jen <henryjen at openjdk.org> wrote:

>> …d on macOS
>> 
>> This patch simply round up the specified stack size to multiple of the system page size. 
>> 
>> Test is trivial, simply run java with -Xss option against following code. On MacOS, before the fix, running with `-Xss159k` and `-Xss160k` would get `7183` and `649` respectively. After fix, both would output `649`, while `-Xss161k` would be same as `-Xss164k` and see 691 as the output.
>> 
>> ```code:java
>> public class StackLeak {
>>     public int depth = 0;
>>     public void stackLeak() {
>>         depth++;
>>         stackLeak();
>>     }
>> 
>>     public static void main(String[] args) {
>>         var test = new StackLeak();
>>         try {
>>             test.stackLeak();
>>         } catch (Throwable e) {
>>             System.out.println(test.depth);
>>         }
>>     }
>> }
>
> Henry Jen 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 seven additional commits since the last revision:
> 
>  - Cast type
>  - Merge
>  - Change java -X output for -Xss
>  - Merge
>  - Only try to round-up when current value failed
>  - Avoid overflow on page size
>  - JDK-8236569: -Xss not multiple of 4K does not work for the main thread on macOS

Hi,

proposed shorter form. Otherwise this looks fine. 

Cheers, Thomas

src/java.base/unix/native/libjli/java_md.c line 666:

> 664:         return page_size * pages;
> 665:     }
> 666: }

Could probably be shortened to something like this:


size_t pagesize = (size_t)sysconf(_SC_PAGESIZE);
return (stack_size + (pagesize - 1)) & ~(pagesize - 1);


or, if you insist on checking for SIZE_MAX:


size_t pagesize = (size_t)sysconf(_SC_PAGESIZE);
size_t max = SIZE_MAX - pagesize;
return stack_size <= max ? (stack_size + (pagesize - 1)) & ~(pagesize - 1) : max;


(I see David requested this, so this is fine, though passing SIZE_MAX to this function will quite likely fail anyway :)

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

PR: https://git.openjdk.java.net/jdk/pull/4256