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| An idea for heap-checking stuffs [message #15678] |
Sun, 04 May 2008 12:06  |
mdelfede
Messages: 1308
Registered: September 2007
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Ultimate Contributor |
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After last bug (still unresolved) of memory corruption on upp compiled under ubuntu hardy, I was thinking about some heap checking stuffs that IMO could be incorporated in upp.
So, the idea (I don't know if somebody already did it!) :
1) Set up a new building flag, for example HEAPCHECK.
2) when code is compiled with HEAPCHECK, do the following:
3) On each dynamic allocation, reserve some more bytes, some before and some after returned pointer, and fill with known data.
For example, if I need 10 bytes, I could reserve 20, like this :
DDDDDAAAAAAAAAADDDDD
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returned pointer here
DDDDD represent the 'spare' allocated bytes, filled with known values.
4) Keep a linked list not only for freed data but also for allocated data. I know that this can slow down much the code, but.... it's just when needed for debugging.
5) create 2 functions, FreeCheck() and UsedCheck() that scans the free and used allocated space and checks for values on DDDDD fileds.
6) allow the ability to switch on/off the heap checking on each allocation/free of memory. That one would slow down much the code, but would also allow to find corruptions just a little after they happens.
Up to here, not much work in upp code, IMHO.
The best would also be to add
7) Add container's methods entry/exit pointer checking. So, for each method called for a container, check container's pointers on method entry and exit. That one would catch 99% of pointer misusage as soon as it happens. Of course, that last one would mean to add a lot of (conditional) code to upp core.
Ciao
Max
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| Re: An idea for heap-checking stuffs [message #15688 is a reply to message #15678] |
Sun, 04 May 2008 18:23  |
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mirek
Messages: 14105
Registered: November 2005
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Ultimate Member |
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| mdelfede wrote on Sun, 04 May 2008 06:06 |
After last bug (still unresolved) of memory corruption on upp compiled under ubuntu hardy, I was thinking about some heap checking stuffs that IMO could be incorporated in upp.
So, the idea (I don't know if somebody already did it!) :
1) Set up a new building flag, for example HEAPCHECK.
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Good idea to actviate heap checks in release mode.
| Quote: |
3) On each dynamic allocation, reserve some more bytes, some before and some after returned pointer, and fill with known data.
For example, if I need 10 bytes, I could reserve 20, like this :
DDDDDAAAAAAAAAADDDDD
|
returned pointer here
DDDDD represent the 'spare' allocated bytes, filled with known values.
|
This is already done (in debug mode).
| Quote: |
4) Keep a linked list not only for freed data but also for allocated data. I know that this can slow down much the code, but.... it's just when needed for debugging.
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Yep, this is also done  BTW, I am using these links as sentinels. And it is also used to check leaks.
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5) create 2 functions, FreeCheck() and UsedCheck() that scans the free and used allocated space and checks for values on DDDDD fileds.
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MemoryCheck.
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6) allow the ability to switch on/off the heap checking on each allocation/free of memory. That one would slow down much the code, but would also allow to find corruptions just a little after they happens.
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Each allocation has serial number. You can set breakpoint to this serial number to catch the very allocation that gets corrupted later.
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Up to here, not much work in upp code, IMHO.
The best would also be to add
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Indeed. Only MEMORYCHECK in release.
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7) Add container's methods entry/exit pointer checking. So, for each method called for a container, check container's pointers on method entry and exit. That one would catch 99% of pointer misusage as soon as it happens. Of course, that last one would mean to add a lot of (conditional) code to upp core.
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That is a good idea. A lot of code involved thought ("each method" 
Mirek
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| Re: An idea for heap-checking stuffs [message #15690 is a reply to message #15688] |
Sun, 04 May 2008 18:45 |
mdelfede
Messages: 1308
Registered: September 2007
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Ultimate Contributor |
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| luzr wrote on Sun, 04 May 2008 18:23 |
| mdelfede wrote on Sun, 04 May 2008 06:06 |
After last bug (still unresolved) of memory corruption on upp compiled under ubuntu hardy, I was thinking about some heap checking stuffs that IMO could be incorporated in upp.
So, the idea (I don't know if somebody already did it!) :
1) Set up a new building flag, for example HEAPCHECK.
|
Good idea to actviate heap checks in release mode.
| Quote: |
3) On each dynamic allocation, reserve some more bytes, some before and some after returned pointer, and fill with known data.
For example, if I need 10 bytes, I could reserve 20, like this :
DDDDDAAAAAAAAAADDDDD
|
returned pointer here
DDDDD represent the 'spare' allocated bytes, filled with known values.
|
This is already done (in debug mode).
|
Yes ? before and after the returned pointer ? that's good !
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| Quote: |
4) Keep a linked list not only for freed data but also for allocated data. I know that this can slow down much the code, but.... it's just when needed for debugging.
|
Yep, this is also done BTW, I am using these links as sentinels. And it is also used to check leaks.
| Quote: |
5) create 2 functions, FreeCheck() and UsedCheck() that scans the free and used allocated space and checks for values on DDDDD fileds.
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MemoryCheck.
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mhhhh... as far as I could see, MemoryCheck does a check on freed blocks, and only on small allocs... or am I wrong ?
Does it check also allocated blocks integrity ?
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| Quote: |
6) allow the ability to switch on/off the heap checking on each allocation/free of memory. That one would slow down much the code, but would also allow to find corruptions just a little after they happens.
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Each allocation has serial number. You can set breakpoint to this serial number to catch the very allocation that gets corrupted later.
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That's very interesting... but how do you see the serial number and how do you set breakpoint ?
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| Quote: |
Up to here, not much work in upp code, IMHO.
The best would also be to add
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Indeed. Only MEMORYCHECK in release.
| Quote: |
7) Add container's methods entry/exit pointer checking. So, for each method called for a container, check container's pointers on method entry and exit. That one would catch 99% of pointer misusage as soon as it happens. Of course, that last one would mean to add a lot of (conditional) code to upp core.
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That is a good idea. A lot of code involved thought ("each method"
Mirek
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yep, but that could be done slowly... I could help for some classes. No hurry on that one
Max
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| Re: An idea for heap-checking stuffs [message #15692 is a reply to message #15690] |
Sun, 04 May 2008 20:13 |
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mirek
Messages: 14105
Registered: November 2005
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Ultimate Member |
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| mdelfede wrote on Sun, 04 May 2008 12:45 |
| luzr wrote on Sun, 04 May 2008 18:23 |
| mdelfede wrote on Sun, 04 May 2008 06:06 |
After last bug (still unresolved) of memory corruption on upp compiled under ubuntu hardy, I was thinking about some heap checking stuffs that IMO could be incorporated in upp.
So, the idea (I don't know if somebody already did it!) :
1) Set up a new building flag, for example HEAPCHECK.
|
Good idea to actviate heap checks in release mode.
| Quote: |
3) On each dynamic allocation, reserve some more bytes, some before and some after returned pointer, and fill with known data.
For example, if I need 10 bytes, I could reserve 20, like this :
DDDDDAAAAAAAAAADDDDD
|
returned pointer here
DDDDD represent the 'spare' allocated bytes, filled with known values.
|
This is already done (in debug mode).
|
Yes ? before and after the returned pointer ? that's good !
| Quote: |
| Quote: |
4) Keep a linked list not only for freed data but also for allocated data. I know that this can slow down much the code, but.... it's just when needed for debugging.
|
Yep, this is also done BTW, I am using these links as sentinels. And it is also used to check leaks.
| Quote: |
5) create 2 functions, FreeCheck() and UsedCheck() that scans the free and used allocated space and checks for values on DDDDD fileds.
|
MemoryCheck.
|
mhhhh... as far as I could see, MemoryCheck does a check on freed blocks, and only on small allocs... or am I wrong ?
Does it check also allocated blocks integrity ?
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Sorry, it is in fact "MemoryCheckDebug". It calls basic MemoryCheck and then goes through the list.
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That's very interesting... but how do you see the serial number and how do you set breakpoint ?
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You should see breakpoint serial number in the .log.
You can set it using "MemoryBreakpoint" function or using --memory_breakpoint commandline option. However, this is not very helpful in our Ubuntu problem as both can get active only AppInit...
Mirek
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