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Authored by kevans on Nov 23 2020, 1:40 AM.

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kib
jhb
trasz

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manpages

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rS368481: kdump/truss: decode new _umtx_op flags

Summary

(These weren't necessarily large enough on their own to split out, but I can commit them separately)

Document the new flags for _umtx_op(2)
Teach libsysdecode about them -- flags use a double underbar after UMTX_OP, command use a single.
Support decoding in kdump -- print the flag bits first, then the command
Same with truss

Test Plan

Observe the output:

ktrace:

root@viper:~/qemu-bsd-user/arm-bsd-user# kdump | grep -i -- _umtx_op | head -5
  2286 qemu-arm CALL  _umtx_op(0x7fffffffe8f0,0x3<UMTX_OP_WAKE>,0x1,0,0)
  2286 qemu-arm RET   _umtx_op 0
  2286 qemu-arm CALL  _umtx_op(0x8605f7008,0xf<UMTX_OP_WAIT_UINT_PRIVATE>,0,0,0)
  2286 qemu-arm CALL  _umtx_op(0x9fffdce8,0x80000003<UMTX_OP__32BIT|UMTX_OP_WAKE>,0x1,0,0)
  2286 qemu-arm RET   _umtx_op 0

These first two calls were indeed pure native ops, and I think this is still sensible looking.

truss samples:

10039 100540: _umtx_op(0x7fffffffda50,UMTX_OP_WAKE,0x1,0x0,0x0) = 0 (0x0)           
10057 100905: _umtx_op(0x9fffdd08,UMTX_OP__32BIT|UMTX_OP_WAKE,0x1,0x0,0x0) = 0 (0x0)

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rS FreeBSD src repository - subversion

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Buildable 34966

Event Timeline

kevans created this revision.Nov 23 2020, 1:40 AM

Herald added a reviewer: manpages. · View Herald TranscriptNov 23 2020, 1:41 AM

Herald added a subscriber: imp. · View Herald Transcript

kevans requested review of this revision.Nov 23 2020, 1:41 AM

Harbormaster completed remote builds in B34966: Diff 79874.Nov 23 2020, 1:41 AM

kib added inline comments.Nov 23 2020, 10:19 AM

lib/libc/sys/_umtx_op.2
1284	I do not think it is enough to say that. You need to really explain what does it mean.

Enumerate the exact implications of the new compat flags
Note the behavior with robust lists

I realized as I was writing this that I've done a terrible thing with robust lists. It returns EBUSY, but libthr will ignore the return value. Moreover, I can't see much room in the spec for this to fail.

This is slightly mitigated by the facts that we won't do robust list init until a robust mutex is entered or initialized, that these are on a per-thread basis, and the new flags are only/mostly useful for emulation.

For the last point, we could probably emphasize that the emulator must check the error from UMTX_OP_ROBUST_LISTS and do the needful, whatever that means.

Harbormaster completed remote builds in B34999: Diff 79929.Nov 24 2020, 11:41 AM

You can make mutex_init_robust() either issue a message, or abort() in case of _umtx_op() returning error.

This revision is now accepted and ready to land.Nov 24 2020, 12:34 PM

kevans mentioned this in rS368479: _umtx_op(2): document recent addition of 32bit compat flags.Dec 9 2020, 3:21 AM

Closed by commit rS368481: kdump/truss: decode new _umtx_op flags (authored by kevans). · Explain WhyDec 9 2020, 3:23 AM

This revision was automatically updated to reflect the committed changes.

kevans mentioned this in rS368480: libsysdecode: decode _UMTX_OP flags.

kevans added a commit: rS368481: kdump/truss: decode new _umtx_op flags.

kevans mentioned this in rG906cd9a167b1: MFC _umtx_op: documentation and libsysdecode/kdump/truss decoding (32-bit).Dec 27 2020, 3:07 AM