Re: [PATCH hurd] libports: use protected payloads to optimize the object lookup

[Samuel Thibault]

Samuel Thibault, le Wed 22 Apr 2015 22:59:30 +0200, a écrit :
> I'm rebuilding an ext2fs.static with -fno-omit-frame-pointer to get more
> backtrace.

db> show task $task1
    TASK        THREADS
  1 ext2fs (f4d68e40): 15 threads:
              0 (f4d693c0) ..SO.F(walking_zombie)
              1 (f4d69140) .WSO.F(exception_raise_continue) 0
              2 (f4d69000) .WSO..(mach_msg_receive_continue) 0
              3 (f4db2dc8) .WSO..(mach_msg_continue) 0
              4 (f4db2c88) .WSO..(mach_msg_receive_continue) 0
              5 (f4db2b48) .WSO.F(mach_msg_continue) 0
              6 (f4db2a08) ..SO.F(mach_msg_receive_continue)
              7 (f4db28c8) ..SO.F(mach_msg_receive_continue)
              8 (f4db2288) .WSO..(mach_msg_receive_continue) 0
              9 (f4dc9c90) .W.O..(mach_msg_continue) 0
             10 (f4dc9a10) ..SO.F(mach_msg_receive_continue)
             11 (f4dc9790) ..SO.F(mach_msg_receive_continue)
             12 (f4e52900) .WSO.F(mach_msg_receive_continue) 0
             13 (f4e527c0) .WSO.F(mach_msg_receive_continue) 0
             14 (f4e52180) .WSO.F(mach_msg_receive_continue) 0
db> trace/tu $task1.1
Continuation exception_raise_continue
>>>>> user space <<<<<
0x807cef5(800de70,800be60,0,2000,a)
0x80b8678(800ff00,2000,a,800,0)
0x807d16e(1,10000,0,0,0)
0x807d354(81d2ff0,805dca0,1d4c0,927c0,0)
0x80660ab(805dca0,0,0,0,0)

0x807cef5
/usr/src/hurd-debian/build-deb/libports/../../libports/ports.h:268,
actually the synchronized_demuxer function, the ports_lookup_payload
call at line 172
0x80b8678
??:?  (but looking by hand, this falls inside mach_msg_server_timeout,
msgserver.c:108, the *demux call)
0x807d16e
/usr/src/hurd-debian/build-deb/libports/../../libports/manage-multithread.c:252
0x807d354
/usr/src/hurd-debian/build-deb/libports/../../libports/manage-multithread.c:279
0x80660ab
/usr/src/hurd-debian/build-deb/libdiskfs/../../libdiskfs/init-first.c:42 
(discriminator 1)

db> x/tx 0x800de70 $task1.1 (i.e. msgh_bits)
                1700
db> x/tx 0x800de74 $task1.1 (i.e. msgh_size)
                20
db> x/tx 0x800de78 $task1.1 (i.e. msgh_remote_port)
                0
db> x/tx 0x800de7c $task1.1 (i.e. msgh_protected_payload)
                f4ed4a2c
db> x/tx 0X800de80 $task1.1 (i.e. msgh_seqno)
                1
db> x/tx 0X800de84 $task1.1 (i.e. msgh_id)
                48

This protected payload looks odd indeed.

Samuel