Issue #9905 has been reported by Rei Odaira.

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Bug #9905: Fiber does not work on AIX
https://bugs.ruby-lang.org/issues/9905

* Author: Rei Odaira
* Status: Open
* Priority: Normal
* Assignee: 
* Category: 
* Target version: 
* ruby -v: ruby 2.2.0dev (2014-06-02 trunk 45270) [powerpc-aix7.1.0.0]
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN
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`test/ruby/test_fiber.rb` fails on AIX.

~~~
[ 2/23] TestFiber#test_argument/ss/home/rayod/Dev/Contribution/ruby-trunk-blue1/test/ruby/test_fiber.rb:19: [BUG] machine_stack_cache size is not canonicalized
ruby 2.2.0dev (2014-06-02 trunk 45270) [powerpc-aix7.1.0.0]
~~~
Here is what happens for this test:
1) A fiber is created by setting `context->uc_stack.ss_size` to a certain value and calling makecontext().
2) While the fiber is switched with other fibers by swapcontext(), `context->uc_stack.ss_size` is changed to a very large value by AIX.
3) When the fiber finishes, its stack pointer and size are cached in `machine_stack_cache[]`.
4) When a new fiber is created, a specified stack size is different from the cached stack size, so the error is thrown.

I feel AIX's behavior is strange, but I also suppose in general, `context->uc_stack.ss_size` is not guaranteed to be preserved after makecontext() or swapcontext(). (Please correct me if I am wrong.)

Rather than disabling `FIBER_USE_NATIVE` for AIX, I propose saving the original stack pointer and size not in `ucontext_t` but in new dedicated fields in `rb_fiber_t`, as you can find in the attched patch. With this patch, `test/ruby/test_fiber.rb` results in no errors on AIX. This did not cause any error on Linux, either, for test or test-all.


---Files--------------------------------
sp_and_size_for_fiber.patch (1.9 KB)


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