truss crashing process

[Kostik Belousov]

On Wed, Jul 27, 2011 at 11:35:49AM -0500, Dan Nelson wrote:
> In the last episode (Jul 27), Alexander Best said:
> > hi there,
> > 
> > i was trying to attach truss to chromium via
> > 
> > 'truss -p 18445' and got:
> > 
> > [...]
> > kevent(26,{},0,{0x1b,EVFILT_READ,0x0,0,0x1,0x44cb600 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x!
>  0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,!
>  0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,0x0,0x0,0,0x0,0x0 0x0,!
>  0x0,0x0,
> > -- UNKNOWN SYSCALL -14720592 --
> > write(-14720976,0x8080808080808000,0)		 = 41 (0x29)
> > select(94,0x6acd,{0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 40 41 42 43 44 45 46 70 71 72 73 76 77 78 79 80 81 82 84 87 88 91},0x1,{0.85048848 }) = 73 (0x49)
> > -- UNKNOWN SYSCALL 303120384 --
> > #94(0x0,0x0,0x5e,0xb6cd600,0x83ed780,0x3dae410)	 = 189 (0xbd)
> > truss: Cannot malloc -14740096 bytes for fd_set array: Cannot allocate memory
> 
> Invalid syscalls numbers like that usually mean that truss has attached to a
> process in the middle of a syscall.  The ptrace API fires the same event for
> syscall enter and exit, so if truss is expecting an enter and gets an exit,
> you get a mangled syscall number and eventually truss will coredump trying
> to decode incorrect data.
> 
> Try applying the patch at https://www.evoy.net/FreeBSD/truss.diff , which
> amongst other things, fixes this problem.  If you just want the syscall fix,
> search the diff for "50-50 chance" and manually patch that if(){} block in
> your source.

We have PL_FLAG_SCE/PL_FLAG_SCX for some time. I planned to update truss
to use the flags, as well as to take advantage of PL_FLAG_FORKED to close
the race where truss can miss the forked child.

Unfortunately, the project stalled.
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