cfbolz changed the topic of #pypy to: #pypy PyPy, the flexible snake | IRC logs: and | the pypy angle is to shrug and copy the implementation of CPython as closely as possible, and staying out of design decisions
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<arigato> cfbolz: found a way to remove the crash
<cfbolz> arigato: very cool
<cfbolz> arigato: of course once they start merging the nogil stuff everything will become way more complicated :-(
<arigato> ah. I think I'm not going to look at all
<cfbolz> :-)
<cfbolz> arigato: probably sensible
<cfbolz> arigato: I have an incredibly random question: do you remember whether we had to do anything special to make gdb understand the JIT's stack frames to make gdb commands like "backtrace" and "up" work? or is our function prologue/epilogue close enough to what a C compiler produces that the gdb pattern can deal with it?
<cfbolz> (if you don't remember that's fine)
<arigato> as far as I remember, gdb out of the box used to understand the frames
<cfbolz> ok, makes sense
<arigato> it might have been accidental, though
<arigato> instead of carefully designed
<cfbolz> yeah, that's kind of what I'm suspecting too
<arigato> (except on Power64, where I remember I needed to make the frames be fully "official" because otherwise some other OS things were not happy)
<cfbolz> interesting
<cfbolz> apparently there's a bunch of different mechanisms for this, eg gdb will to abstract interpretation to find the frame pointer on some CPUs
<arigato> ah, cool
<cfbolz> there seems to be a bug in the subtraction implementation:
<cfbolz> the constant_last (&a, &b); call will swap the arguments, which is incorrect because subtract isn't commutative
<cfbolz> I haven't decided whether I want to send a patch (by mail) yet though :-)
<arigato> :-)
<arigato> "constant - nonconstant" should always be pvk_unknown
<arigato> how on earth did you find this bug?
<cfbolz> arigato: just randomly looked at the code :-)
<arigato> right, it has abstract interpretation in the description after all :-)
<cfbolz> the long story is: was chatting with some cpython devs that have a JIT prototype, and for the gdb didn't manage to understand the frames
<cfbolz> so I got curious how it works
<cfbolz> (the abstract interpretation is not used on x86 though, but arm 64 and some others)
<arigato> cool
<cfbolz> it seems to be a mess though, eg linux perf doesn't do anything like this, and you need to emit dwarf frame descriptions at runtime if you want to sample the full stack
<fijal> hi!
<fijal> are you sure that (Py_ssize_t)refcount < 0 cannot be optimized away by C compiler?
<sam_> the gdb people are rather nice and might be worth asking them in #gdbt oo
<sam_> *#gdb too
<cfbolz> sam_: thanks :-)
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<cfbolz> arigato: the nogil work is 77 pull requests 😆
<cfbolz> they merged 9
<Alex_Gaynor> cfbolz: how did you find all 77, I'm failing to find with search
<cfbolz> Alex_Gaynor: "private communication"
<Alex_Gaynor> 👍
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