DBG C RangeStep

Debug Command 26 - Range Step Command

Parameters

• Pid= Process ID of debuggee
• Tid= Thread ID of thread to range-step
• Cmd= DBG_C_RangeStep
• Value= Linear address denoting start of range (exclusive)
• Addr= Linear address denoting end of range (exclusive)

Returns

The RangeStep notification is usually returned, but any Debug notification may be returned. See DosDebug Notifications for more information.

This command allows a debugger to specify a range of addresses (bounded by the linear addresses in the Value and Addr fields) through which a debuggee thread should single-step until one of the following conditions occurs:

• The debuggee thread's linear EIP (instruction pointer) is outside the range.
• The linear EIPs of consecutive debuggee threads are the same.
• Some other notification occurs.

When the DBG_C_RangeStep command returns, the register set is automatically updated to reflect the thread that detected the event.

Callgates that result in a privilege level transition to ring 0 will appear to range-step as a single instruction, with the range-step continuing after the function completes. This hides ring 0 execution from debuggers.

Attempting to range-step a thread that is frozen results in an error.

Restrictions

To accomplish callgate single-stepping, the single-step must be simulated because the flags (specifically, the TF bit) are not stored in the ring 0 callgate stack frame. Because of this, a range-step that results in leaving a ring 0 callgate will sometimes not execute any user-space code. The following range-step should function normally.

Range-stepping some REP instructions may not work correctly due to errors in the 80386 processor.