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Fix crash on PtraceCleanup #61
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I think this may also fix #60. The SYSCALL-ADD-ADD-ADD in the disassembly (just after another SYSCALL, where it couldn't possibly work) in that issue is similar to what I've seen - |
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Interesting. There are a lot of weird idiosyncrasies around ptrace, so yeah, this may be necessary. |
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* origin/master: Fix crash on PtraceCleanup (uber-archive#61)
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I found I was getting a crash, due to an unhandled SIGTRAP, the second time I profiled a process with
--threads. My initial thought was that this was because themunmapstuff was not thread safe (it doesn't pause threads while poking instructions into code), so fixed this.However, I was wrong. The real issue is that for reasons I don't fully understand, the
PtraceCleanupisn't successful unless we explicitly detach from the process - implicitly detaching by exiting does not seem to be sufficient. I've added an explicitPtraceDetach, and I don't see the issue any more.I've also modified
PtraceAttachto usewaitpidwith__WALL. This was mostly done as a debugging measure (one theory was that maybe it was stopping on the wrong thing, so I thought tightening up the wait logic might force it to fail earlier), although it may have the side effect of allowing--threadson pre-4.9 kernels, so I've left it in.