s390x runtime: use unsigned comparisons for "less than" comparisons between pointers#12258
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xavierleroy merged 1 commit intoocaml:trunkfrom May 24, 2023
Merged
s390x runtime: use unsigned comparisons for "less than" comparisons between pointers#12258xavierleroy merged 1 commit intoocaml:trunkfrom
xavierleroy merged 1 commit intoocaml:trunkfrom
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With the unsigned comparisons, the strange ocamlopt.opt crash in testsuite/tests/callback/callback_effects_gc.ml goes away. |
lthls
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May 23, 2023
| /* Copy arguments from OCaml to C stack */ | ||
| LBL(105): | ||
| lay %r8, -8(%r8) | ||
| cgr %r8, %r9 |
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Just to be sure: this one is unrelated to the testsuite failure, but fixes potential errors if the OCaml stack pointer is close to 0x8000000000000000. Correct ?
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Correct! All comparisons between pointers should be unsigned, because signed compares give wrong results around the "equator" (2^63 or 2^31).
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When comparing the young pointer with the young limit, or the stack pointer with some bound, always use unsigned comparisons (
clginstruction), not signed comparisons (cg). The latter causes surprises like #11712 (comment)