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

[David Holmes]

On Fri, 28 May 2021 21:55:24 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);
>         }
>     }
> }

src/java.base/macosx/native/libjli/java_md_macosx.m line 727:

> 725: 
> 726: static size_t alignUp(size_t stack_size) {
> 727:     long page_size = sysconf(_SC_PAGESIZE);

In hotspot we use `getpagesize()`. There is also a guard for a very large stack (within a page of SIZE_MAX) so that rounding up does not produce zero.

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