PMSEM/GRESEM

32-bit PM (WARP) and Graphics Engine use a composite semaphore structure to serialise their resources.

This semaphore has the structure:

• 0x0
  7 byte Signature. 'PMSEM' for PMWIN and 'GRESEM' for PMGRE
  +0x7
  386 semaphore byte (PM uses the bts instruction on this under 386 processors otherwise it uses the 486 cmpxchg on the pid/tid)
  +0x8
  Owner pid (word)
  +0xa
  Owner tid (word)
  +0xc
  Owner nested use count (long)
  +0x10
  Number of waiters
  +0x14
  Number of times sem used (zero unless Debug version of PM)
  +0x18
  Handle for event semaphore
  +0x1c
  Address of caller (zero unless Debug version of PM)

  PM uses a technique of polling this semaphore by waiting on the imbedded event semaphore handle for a limited time.

  This technique has the advantage of speed combined with accountability but a thread waiting for a PMSEM or GRESEM may appear blocked, ready or running depending on the polling cycle. However it will be executing in a routine with a name such as PMRequestMutexSem. If the PMMERGE symbols are loaded this is readily detected.

  The PM and GRE SEMs are contiguous and located at label pmSemaphores.

  The handle (linear address) of the PM/GRE Semaphore is passed on entry to PMREquestMutexSem and tends to be retained in the EDX register.

  The following semaphores are defined by PM:

• PMSEM ATOM

• PMSEM USER

• PMSEM VISLOCK

• PMSEM DEBUG

• PMSEM HOOK

• PMSEM HEAP

• PMSEM DLL

• PMSEM THUNK

• PMSEM XLCE

• PMSEM UPDATE

  10

  PMSEM CLIP
  11
  PMSEM INPUT
  12
  PMSEM DESKTOP
  13
  PMSEM HANDLE
  14
  PMSEM ALARM
  15
  PMSEM STRRES
  16
  PMSEM TIMER
  17
  PMSEM CONTROLS
  18
  GRESEM GreInit
  19
  GRESEM AutoHeap
  20
  GRESEM PDEV
  21
  GRESEM LDEV
  22
  GRESEM CodePage
  23
  GRESEM HFont
  24
  GRESEM FontCntxt
  25
  GRESEM FntDrvr
  26
  GRESEM ShMalloc
  27
  GRESEM GlobalData
  28
  GRESEM DbcsEnv
  29
  GRESEM SrvLock
  30
  GRESEM SelLock
  31
  GRESEM ProcLock
  32
  GRESEM DriverSem
  33
  GRESEM semIfiCache
  34
  GRESEM semFontTable

  In this example one of the shell threads seems to be getting very little CPU, though is frequently ready:

  # .p 3a Slot  Pid  Ppid Csid Ord  Sta Pri  pTSD     pPTDA    pTCB     Disp SG Name
  *003a# 000d 0005 000d 000a rdy 0200 abd61000 abe4b5b4 abe2ee60 0ee4 11 PMSHL32
  
  # .r
  eax=13e30025 ebx=00000000 ecx=000a000d edx=13e7b4d4 esi=ffffffff edi=0068e55c
  eip=1bd0d7ea esp=00637f44 ebp=00637f60 iopl=2 -- -- -- nv up ei pl nz na po nc
  cs=005b ss=0053 ds=0053 es=0053 fs=150b gs=0000  cr2=00000000  cr3=001ad000
  005b:1bd0d7ea ff4a10         dec     dword ptr [edx+10]    ds:13e7b4e4=00000006
  
  # ln
  %1bd0d770 PMMERGE PMREQUESTMUTEXSEM + 7a
  
  # db %edx
  %13e7b4d4 50 4d 53 45 4d 00 00 00-10 00 01 00 02 00 00 00 PMSEM...........
  %13e7b4e4 06 00 00 00 00 00 00 00-05 00 01 80 00 00 00 00 ................
  %13e7b4f4 50 4d 53 45 4d 00 00 00-00 00 00 00 00 00 00 00 PMSEM...........
  %13e7b504 00 00 00 00 00 00 00 00-06 00 01 80 00 00 00 00 ................
  %13e7b514 50 4d 53 45 4d 00 00 00-00 00 00 00 00 00 00 00 PMSEM...........
  %13e7b524 00 00 00 00 00 00 00 00-07 00 01 80 00 00 00 00 ................
  %13e7b534 50 4d 53 45 4d 00 00 00-00 00 00 00 00 00 00 00 PMSEM...........
  %13e7b544 00 00 00 00 00 00 00 00-08 00 01 80 00 00 00 00 ................
  
  >> PMSEM owner is pid 10 tid 1 and it has been requested twice by
  tid/pid 10/1. There are 6 waiting threads.
  
  # .p 42
   Slot  Pid  Ppid Csid Ord  Sta Pri  pTSD     pPTDA    pTCB     Disp SG Name
   0042  0010 0005 0010 0001 blk 0500 abd69000 abe4c19c abe2fe20 0ed8 13 MRFILEPM
  
  # .pb 42
   Slot  Sta BlockID  Name     Type        Addr        Symbol
   0042  blk fdf8841c MRFILEPM
  
  >> The owner is blocked.
  
  # .m %fdf8841c
  
  *har     par      cpg        va    flg next prev link hash hob   hal
   0003 %feeef04c 00001000 %fdeef000 001 0002 0021 0000 0000 0003 0000      =0000
   hob   har hobnxt flgs own  hmte  sown,cnt lt st xf
   0003  0003 ff05  0000 ffec 0000  0000 00  02 00 00 vmkrhrw
  
  # dd %fdf8841c-10 l4
  %fdf8840c  000101c1 00000000 fdf88406 ffc20018
  
  # .mo ffc2
  ffc2 semstruc
  
  # .d sem32 %fdf8841c
          Type: Shared Event
         Flags: Reset
         pMuxQ: 00000000
    Post Count: 0000
        pOpenQ: fde305f8
         pName: NULL (anonymous)
   Create Addr: abe2fe20
  
  # .d openq  %fde305f8
  
    PID   Open Count
    ----------------
    0010     0001
  
  #
  # ln pmsemaphores
  9f3f:0000b4b4 PMMERGE PMSEMAPHORES
  # dl 9f3f
  9f3f  Data    Bas=13e70000 Lim=0000ffff DPL=3 P  RW    A
  #
  >> The sem we were waiting on was at %13e7b4d4 so must be the
  >> USER SEM.
  

  ---

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