OpenEuphoria

1. Debugging "A machine-level exception"

• Posted by marky1124 Aug 21, 2008
• 1050 views

Hi,

I look after a few applications that crash from time to time. Usually I can use the ex.err to track down the fault in the source code. Occassionally the crash message is "A machine level exception occurred during execution of this statement". These ones leave me a little nonplussed. The crashes occur infrequently and across a large range of different machines. Whenever I ask the user for more information I get the conversational equilvalent of a shrug. The users are half way across the country from me, and so I can't watch it happen and the user can't reproduce it.

Can anyone offer me some help on how to diagnose faults like this one

• C:\EUPHORIA\include\machine.e:296 in function allocate_string()
  A machine-level exception occurred during execution of this statement
  s = {}
  mem = <no value>
  

• ... called from .\Common\Private\dlla2.e:121 in function dllFunc()
  nama = {71'G',101'e',116't',80'P',114'r',105'i',118'v',97'a',116't',101'e',
  80'P',114'r',111'o',102'f',105'i',108'l',101'e',83'S',116't',114'r',105'i',
  110'n',103'g',65'A'}
  par = {
  9702016,
  9702016,
  {},
  {32' ',32' ',32' ',32' ',32' ',32' ',32' ',32' ',32' ',32' ',
  32' ',32' ',32' ',32' ',32' ',32' ',32' ',32' ',32' ',32' ',32' ',32' ',
  32' ',32' ',32' ',32' ',32' ',32' ',32' ',32' ',32' ',32' ',32' ',32' ',
  32' ',32' ',32' ',32' ',32' ',32' ',32' ',32' ',32' ',32' ',32' ',32' ',
  <snip>
  

or this one

• C:\EUPHORIA\Private/eucom.ew:1626 in function quick_activate()
  A machine-level exception occurred during execution of this statement
  obj_ix = 1
  fore_color = 0
  back_color = 16777215
  pfont = 12771300
  this = 8743612
  clientsite = 1293764
  advisesink = 0
  pcontainer = <no value>
  pcontrol = <no value>
  mset = 8733316
  ok = <no value>
  ppvIFont = 1623196
  riid = 9406540
  ppvClient = <no value>
  ppvAdvise = <no value>
  ppvUnk = <no value>
  iocs = <no value>
  duh = <no value>
  vtbl = <no value>
  

• ... called from C:\EUPHORIA\Private/eucom.ew:2422 in procedure init_control()
  obj_ix = 1
  ok = <no value>
  mset = <no value>
  <snip>
  

Cheers,
Mark
P.S. I'm sorry if my use of forum tags is all wrong. I tried a large number of combinations before settling on this look.

3. Re: Debugging "A machine-level exception"

• Posted by gbonvehi Aug 21, 2008
• 1093 views

Sorry about the badly formatted message.
Regarding the second error again, here's some code that will help you debug that one.
According to the documentation, OleCreateFontIndirect returns E_INVALIDARG, E_OUTOFMEMORY, E_UNEXPECTED, E_NOINTERFACE and E_POINTER errors.
Eucom has routines to check for errors, they're just not used there, until now :)
On eucom.ew, quick_activate function add below the line:

    ok = c_func( OleCreateFontIndirect, { pfont, riid, ppvIFont } ) 

This code:

    if is_error(ok) then 
        com_err_out(1)  -- Print the error on console 
        com_error(ok)   -- Display the error on console 
        while get_key() = -1 do -- Wait for key press 
        end while 
        ?1/0 -- Crash 
    end if 

5. Re: Debugging "A machine-level exception"

• Posted by marky1124 Aug 22, 2008
• 1039 views

    ok = c_func( OleCreateFontIndirect, { pfont, riid, ppvIFont } ) 

    if is_error(ok) then 
        com_err_out(1)  -- Print the error on console 
        com_error(ok)   -- Display the error on console 
        while get_key() = -1 do -- Wait for key press 
        end while 
        ?1/0 -- Crash 
    end if 

Hi gbonvehi, bernie,

Thank you for your replies. I certainly am not ruling out the cause being a memory fault, but I'm not 100% sure how to judge. Still pursuing the 2nd crash if we look at the values we see

• pfont = 12771300
• mset = 8733316
• ppvIFont = 1623916
• riid = 9406540

None are a NULL value.

I like your suggestion to do proper error checking, however the crash was attributed to this line 1626:-

    ok = c_func( OleCreateFontIndirect, { pfont, riid, ppvIFont } ) 

so we'd not get a chance to do any subsequent is_error(ok) checks since we've already crashed. Presumably we should be checking the return values from

    ppvIFont = w32acquire_mem( mset, 4 ) 
    riid = w32acquire_mem( mset, string_to_guid( IFont_ ) ) 

Would they be NULL if there was no memory available?

We crashed within OleCreateFontIndirect. I found the OleCreateFontIndirect documentation, thank you for suggesting that. So I'm guessing the most important thing would be to try and see what that call returned.

How can I go about achieving that?
Is it possible from the ex.err I already have?

Cheers,
Mark

7. Re: Debugging "A machine-level exception"

• Posted by marky1124 Aug 27, 2008
• 962 views

-- Isn't ppvIFont a pointer to a pointer ?? 
 
atom output_variable, ppvIFont  
 
  output_variable = w32acquire_mem( mset, 4 ) 
  ppvIFont = w32acquire_mem( mset, 4 ) 
  poke4(ppvIFont,output_variable) 
 
-- ppvIFont now contains pointer to the output_variable pointer.  

I don't know. I've searched my source code and I don't have those lines at all. Perhaps I have a different eucom. I downloaded and checked and I have the latest (v2.08).

My main concern is how to tackle this sort of crash.

Cheers, Mark

9. Re: Debugging "A machine-level exception"

• Posted by CChris Aug 29, 2008
• 959 views

4-6 weeks ago, I suuggested adding dep.zip, or whatever it is called, to the interpreter, but there has been no discussion on the topic that I'm aware of.

CChris