diegor (Diego Russo)1 Hello,
In the past few weeks I’ve been looking at the JIT implementation a little bit more closely. As part of this investigation I wanted to “see” what assembly code was generated that matched the bytecode instruction.
Usingcapstone, I patched the_PyJIT_Compile function to print the mapping to stdout at runtime. It is something like:
...============================================_LOAD_FAST_2 { ffff937ac218 ldr x8, [x0, #0x58] ffff937ac21c ldr w9, [x8] ffff937ac220 adds w9, w9, #1 ffff937ac224 b.hs #0xffff937ac22c ffff937ac228 str w9, [x8] ffff937ac22c str x8, [x1], #8}============================================_SET_IP { ffff937ac230 ldr x8, #0xffff937ac6a8 ffff937ac234 nop ffff937ac238 str x8, [x0, #0x38] ffff937ac23c b #0xffff937ac240}============================================_GUARD_BOTH_INT { ffff937ac240 ldr x8, #0xffff937ac6b0 ffff937ac244 nop ffff937ac248 ldur x9, [x1, #-0x10] ffff937ac24c ldr x9, [x9, #8] ffff937ac250 cmp x9, x8 ffff937ac254 b.ne #0xffff937ac268 ffff937ac258 ldur x9, [x1, #-8] ffff937ac25c ldr x9, [x9, #8] ffff937ac260 cmp x9, x8 ffff937ac264 b.eq #0xffff937ac26c ffff937ac268 b #0xffff937ac5c0 ffff937ac26c b #0xffff937ac270}
This is a quirky way to do it, but I was wondering if such functionality would be useful at all.
If we were to implement it, one possible way to do it is similarly to thedis module (or even extend thedis module).
Thoughts?
Tagging@brandtbucher for awareness.
Thanks
3 Likes
Very cool! It would definitely be useful for debugging the JIT itself, I think. Your implementation seems very similar to our use of thePYTHON_LLTRACE environment variable for debugging the tier one interpreter and tier two optimization pipeline.
This also reminds me of aPR (that I forgot about!) by@tonybaloney allowing one to obtain byte strings of the compiled code from pure-Python (at least, for those who know where to look, using secret APIs designed for tests). It looks likecapstone has aPython API that users could simply pass these strings to to obtain objects representing the assembly code… super cool! So perhaps that could be a way forward here, without introducing a hard dependency oncapstone in CPython itself.
Separately: feel free to reach out if you have any questions or comments about the JIT.
2 Likes
diegor (Diego Russo)4 Thanks for the pointers, very useful indeed! If there is interest then I’ll try to put together a draft PR at some point and I’ll ping you here for review/feedback.
Thanks
