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Re: [Help-smalltalk] [PATCH 2/2] jit: Resume the method _after_ the inte
Re: [Help-smalltalk] [PATCH 2/2] jit: Resume the method _after_ the interrupt check
Tue, 07 Jan 2014 11:49:10 +0100
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Il 03/01/2014 20:15, Holger Hans Peter Freyther ha scritto:
> On Mon, Dec 23, 2013 at 10:32:41PM +0100, Holger Hans Peter Freyther wrote:
> Good Evening,
>>> st> a := 0. p := [a := 3] newProcess
>>> The code does not get across Dictionary>>findIndex: (Dictionary.st:588).
>> if (!lbl_define (*this_label))
>> define_ip_map_entry (bp - bc);
>> emit_interrupt_check (JIT_NOREG, bp - bc);
>> An instance of MethodContext
>> parent: Dictionary(HashedCollection)>>findIndexOrNil: (HashedColl.st:359)
>> nativeIP: 0
> ^^^^ this is the hint. the returned native_ip was not satisfying
> the IS_INT test. This means I had to move the jit_align(2) _after_
> the ip storing.
More precisely, just before the jit_get_label().
> I think this code can be quite fragile when porting
> to other architectures?!
Most other architectures (all other architectures supported by
lightning, at least) do not have instructions that aren't naturally
aligned. That is, 4-byte instructions are 4-aligned.
It can break only on x86, as you experienced, but jit_align() takes care
I guess Thumb would be a problem, since the length of the instruction is
encoded in the bottom bit of PC: bit 0 = 0 means the 4-byte ARM
instruction set, bit 0 = 1 means the 2-byte Thumb instruction set.
GET_CONTEXT_IP and GET_NATIVE_IP would not work in that case.