Re: [rvm-research] Potential issues with longjmp in bootImageRunner

>>> There are a number of approaches to dealing with this:
>>>  1. assume allocation will always be top-down and ignore,
>>>  2. explicitly allocate thread stacks (these can be passed to pthread_create),
>>>  3. replace use of setjmp/longjmp with savecontext/swapcontext
>>> (although these are deprecated in POSIX),
>>>  4. implement a local version of longjmp without a check,
>>>  5. bypass the __longjmp_chk by using glibc's internal __libc_longjmp().
>>>
>>> Disregarding (1), (5) is the smallest change set.
>>
>> I'd also disregard (1). (3) and (4) don't seem attractive to me; we
>> ought to rely on non-deprecated methods from the system libraries as
>> much as possible.
>
> My opinion is (3) the best option as (2) requires the bootImageRunner
> to allocate memory at a specific place in memory and manage it
> (because thread heap will need to be freed).  Instead of
> reimplementing setjmp/longjmp completely, bootThread already has to be
> implemented in machine specific assembly to pivot the stack when
> entering the VM, the existing code should hence be extended to allow
> for pivoting back onto the thread stack.  In effect bootThread should
> return when sysThreadTerminate is called.

It has been pointed out to me that where I said (3), I meant (4).  I
agree that the use of deprecated APIs is not a good option.  An
possible extension to (2) is to use the explicitly allocated stacks
from inside the VM and entirely bypass the allocated of thread stacks
in C/C++.  Although issues regarding the primordial thread would still
need to be addressed.

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