{"action":"created","issue":{"url":"https://api.github.com/repos/mozilla/rr/issues/1448","labels_url":"https://api.github.com/repos/mozilla/rr/issues/1448/labels{/name}","comments_url":"https://api.github.com/repos/mozilla/rr/issues/1448/comments","events_url":"https://api.github.com/repos/mozilla/rr/issues/1448/events","html_url":"https://github.com/mozilla/rr/issues/1448","id":63880234,"number":1448,"title":"Divergence bug recording/replaying Firefox mochitest","user":{"login":"rocallahan","id":296135,"avatar_url":"https://avatars.githubusercontent.com/u/296135?v=3","gravatar_id":"","url":"https://api.github.com/users/rocallahan","html_url":"https://github.com/rocallahan","followers_url":"https://api.github.com/users/rocallahan/followers","following_url":"https://api.github.com/users/rocallahan/following{/other_user}","gists_url":"https://api.github.com/users/rocallahan/gists{/gist_id}","starred_url":"https://api.github.com/users/rocallahan/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/rocallahan/subscriptions","organizations_url":"https://api.github.com/users/rocallahan/orgs","repos_url":"https://api.github.com/users/rocallahan/repos","events_url":"https://api.github.com/users/rocallahan/events{/privacy}","received_events_url":"https://api.github.com/users/rocallahan/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"milestone":null,"comments":2,"created_at":"2015-03-24T02:07:54Z","updated_at":"2015-03-24T02:09:40Z","closed_at":null,"body":"Ben Turner found this. I'm writing some notes here.\r\n\r\nThere's an overshoot. Always reproduces when replaying this trace, but recording the same test at least one other time doesn't show the bug.\r\n```\r\n[ERROR /home/bent/src/mozilla/rr/rr/src/ReplaySession.cc:532:guard_overshoot() errno: 0 'Success'] \r\n -> Replay diverged.  Dumping register comparison.\r\n[FATAL /home/bent/src/mozilla/rr/rr/src/ReplaySession.cc:549:guard_overshoot() errno: 0 'Success'] \r\n (task 17669 (rec:13374) at time 56977)\r\n```\r\n\r\nApart from the ticks value being wrong, the registers are almost but not quite matching:\r\n````\r\n rax:0x1 rbx:0x0 rcx:0x70000004 rdx:0x511fa0861ef54 rsi:0x0 rdi:0x2aaacb0811c0 rbp:0x7fffffffb5a0 rsp:0x7fffffffb530 r8:0x7fffffffb430 r9:0x7fffffffb0d8 r10:0x8 r11:0x60 r12:0x2aaaae2df638 r13:0x2aaaae3af946 r14:0x0 r15:0x0 rip:0x2aaab2b7e27a eflags:0x293 cs:0x33 ss:0x2b ds:0x0 es:0x0 fs:0x0 gs:0x0 orig_rax:0xffffffffffffffff\r\n\r\nrax            0x1\t1\r\nrbx            0x0\t0\r\nrcx            0xffffffffffffffff\t-1\r\nrdx            0x511fa0861ef54\t1427140463685460\r\nrsi            0x0\t0\r\nrdi            0x2aaacb0811c0\t46913039110592\r\nrbp            0x7fffffffb5a0\t0x7fffffffb5a0\r\nrsp            0x7fffffffb530\t0x7fffffffb530\r\nr8             0x7fffffffb430\t140737488335920\r\nr9             0x7fffffffb0d8\t140737488335064\r\nr10            0x8\t8\r\nr11            0x60\t96\r\nr12            0x2aaaae2df638\t46912555054648\r\nr13            0x2aaaae3af946\t46912555907398\r\nr14            0x0\t0\r\nr15            0x0\t0\r\nrip            0x2aaab2b7e27a\t0x2aaab2b7e27a <js::GCMarker::saveValueRanges()+890>\r\neflags         0x293\t[ CF AF SF IF ]\r\n````"},"comment":{"url":"https://api.github.com/repos/mozilla/rr/issues/comments/85293329","html_url":"https://github.com/mozilla/rr/issues/1448#issuecomment-85293329","issue_url":"https://api.github.com/repos/mozilla/rr/issues/1448","id":85293329,"user":{"login":"rocallahan","id":296135,"avatar_url":"https://avatars.githubusercontent.com/u/296135?v=3","gravatar_id":"","url":"https://api.github.com/users/rocallahan","html_url":"https://github.com/rocallahan","followers_url":"https://api.github.com/users/rocallahan/followers","following_url":"https://api.github.com/users/rocallahan/following{/other_user}","gists_url":"https://api.github.com/users/rocallahan/gists{/gist_id}","starred_url":"https://api.github.com/users/rocallahan/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/rocallahan/subscriptions","organizations_url":"https://api.github.com/users/rocallahan/orgs","repos_url":"https://api.github.com/users/rocallahan/repos","events_url":"https://api.github.com/users/rocallahan/events{/privacy}","received_events_url":"https://api.github.com/users/rocallahan/received_events","type":"User","site_admin":false},"created_at":"2015-03-24T02:09:40Z","updated_at":"2015-03-24T02:09:40Z","body":"Because this is a debug build, `rcx` doesn't get used much. It doesn't appear to have been set in `saveValueRanges` since the code there always sets it to a multiple of 8."}}