| Title | MPS (diagnostic variety only) floating point exception after a collection |
| Status | closed |
| Priority | optional |
| Assigned user | Richard Kistruck |
| Organization | Ravenbrook |
| Description | MPS (diagnostic variety only) floating point exception after a collection Normal varieties of MPS 1.109.1 are not affected by this issue. The diagnostic variety of MPS 1.109.1 has extra code to report memory statistics after each collection. Occasionally, if there is nothing (or almost nothing) to collect, the code emitting this diagnostic information attempts to divide by zero, causing a crash. (Depending on the platform, this may be reported as "floating point exception", "arithmetic exception", "divide by zero", etc). The faulty code is only present in the diagnostic variety of MPS 1.109.1. |
| Analysis | RHSK 2010-03-29 Reproduce with master/...@170103; make -f xci3gc.gmk VARIETY=di zcoll; ./xci3gc/di/zcoll 670759320. The faulty code is in arenavm.c/VMCompact(), inside a "DIAG(" block. So it is compiled-away in non-diagnostic varieties. Fault: Size livePerc = live / (trace->condemned / 100); Fix: check for zero before dividing! |
| How found | unknown |
| Evidence | Found by chance with test-runner. The magic of rnd(). |
| Observed in | 1.109.1 |
| Introduced in | 1.109.1 |
| Created by | Richard Kistruck |
| Created on | 2010-03-29 17:27:37 |
| Last modified by | Richard Kistruck |
| Last modified on | 2010-11-06 21:19:54 |
| History | 2010-03-29 RHSK Created. 2010-04-26 RHSK arenavm.c, not arena.c 2010-11-06 RHSK Optional not critical, because it is in diagnostic variety only, not shipped code. |
| Change | Effect | Date | User | Description |
|---|---|---|---|---|
| 170441 | closed | 2010-04-26 16:06:36 | Richard Kistruck | MPS br/vmem arenavm.c: (diagnostic variety only) fix floating point exception after a collection with 0 bytes condemned The VMCompact diag was calculating the live percentage by dividing by condemned size. Don't do this if condemned is zero. |