| Title | Developers can't debug MPS on OS X. |
| Status | closed |
| Priority | essential |
| Assigned user | Gareth Rees |
| Organization | Ravenbrook |
| Description | Cannot debug MPS on OS X. It seems that once a process on OS X has taken a barrier hit, it is impossible to continue the process from within gdb, the debugger. Either this really is impossible (which is essentially a bug in OS X) or we can't figure out how to. Here's an example gdb session: (gdb) run Starting program: /Users/drj/info.ravenbrook.com/project/mps/master/code/xci3gc/ci/amcss Reading symbols for shared libraries . done Randomizing 28358 times. ........... Program received signal EXC_BAD_ACCESS, Could not access memory. Reason: KERN_PROTECTION_FAILURE at address: 0x005df6b8 0x000046e9 in dylan_write (addr=0x5df6ac, refs=0x61780, nr_refs=180) at fmtdytst.c:165 165 p[i] = (mps_word_t)refs[(r >> 1) % nr_refs]; /* random ptr */ Now at this point we ought to be able to type: handle EXC_BAD_ACCESS nostop into gdb, and have it observe the signal, but pass it through to the process without stopping. (We could then continue the process being debugged with "continue") Unfortunately what happens is that the process and the debugger enter an infinite loop. This makes it essentially impossible to use gdb to do any debugging of the MPS on OS X. |
| Analysis | This can be solved in GDB by "set dont-handle-bad-access 1" and "handle SIGBUS pass nostop noprint" <http://stackoverflow.com/questions/204...b-set-a-breakpoint-for-a-sigbus-handler>. There does not seem to be an equivalent in LLDB. We must document this for people developing with the MPS. |
| How found | unknown |
| Evidence | See Description. |
| Observed in | 1.107.0 |
| Created by | David Jones |
| Created on | 2007-07-09 16:56:34 |
| Last modified by | Gareth Rees |
| Last modified on | 2012-10-22 13:03:42 |
| History | 2007-07-09 DRJ Created. 2012-08-15 RB Added workaround and changed to documentation job. |
| Change | Effect | Date | User | Description |
|---|---|---|---|---|
| 180005 | closed | 2012-10-22 13:03:42 | Gareth Rees | Be clear that the "dont-handle-bad-access" workaround is Mac OS X specific. |