s390x: fix register corruption in runtime #12919
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This was referenced Jan 19, 2024
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cc maybe @xavierleroy , who knows about s390x |
gasche
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I believe that this PR is correct, and propose to merge in trunk and 5.2.
gasche
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We have been very lucky not to notice any ill-effect from this, but gcc 14 apparently uses r12 more aggressively and this bug causes tests/callback/callback_effects_gc.ml to reliably cause a segmentation fault without this fix.
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s390x: fix register corruption in runtime (cherry picked from commit de22ce0)
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This is the fix for #12917. It turns out
caml_callback2_asmuses a callee-saved register without saving it, and we have been incredibly lucky this was not noticed until this week.Rather than save then restore that register, I'm using another
incoming argumenttemporary register as the temporary in this case. This makes the diff almost trivial and easy to check. I also seized the opportunity to add a warning notice about r12 usage to our future selves.It would be nice if this could also get backported to 5.2.