Guarding Memory Blocks: dheap -guards

When your program allocates a memory block, MemoryScape can surround this block with additional memory. It will also initialize this memory to a bit pattern. When MemoryScape checks these blocks, it can tell if your program overwrote the blocks.

Checks can be made in the following ways:

Use the dheap –guard –check command while the process is stopped. MemoryScape will respond by writing information about all overwritten guard blocks.

Use the dheap –notify command. If you’ve turned on notification, MemoryScape checks guard blocks when your program deallocates a memory block. If that memory block’s guards were altered, the CLI stops program execution and MemoryScape writes information.

You should set the TotalView VERBOSE setting to WARNING. Setting it lower than this suppresses this output. Setting it higher tends to bury the information in debugger runtime information.

Use the dheap –guard –set command to turn this feature on or off. To see guard block status, use the dheap –guard command without an argument. For example:

d1.<> dheap -guard

Size Pattern

process: Enabled Max Pre Post Pre Post

1 (13071): yes 0 8 8 0x77777777 0x99999999

If you are using the dheap –info command, you can include guard block information in the output by typing dheap –info –show_guard_settings.