Runtime Checking Eight Megabyte Limit

Only access checking has this limit. Leak checking is not affected by this limit.

On V9, you can work around the eight megabyte limit by using the setenv command to set the USE_FASTTRAPS environment variable to 1. This workaround makes dbx run more slowly and use more memory.

For access checking, RTC replaces each load and store instruction with a branch instruction that branches to a patch area. This branch instruction has an eight megabyte range. If the debugged program has used up all the address space within eight megabytes of the particular load/store instruction being replaced, there is no place to put the patch area. If RTC can't intercept all loads and stores to memory it cannot provide accurate information and so disables access checking completely.

dbx internally applies some strategies when it runs into this limitation and continues if it can rectify this problem. In some cases dbx cannot proceed; it turns off access checking after printing an error message. For workarounds, see Chapter 9, Using Runtime Checking." For more information on the eight megabyte limit, see "RTC's Eight Megabyte Limit".