5.5.6 Observer Mode

If you want to build on non-stop mode and observe program behavior without any chance of disruption by GDB, you can set variables to disable all of the debugger’s attempts to modify state, whether by writing memory, inserting breakpoints, etc. These operate at a low level, intercepting operations from all commands.

When all of these are set to off, then GDB is said to be observer mode. As a convenience, the variable observer can be set to disable these, plus enable non-stop mode.

Note that GDB will not prevent you from making nonsensical combinations of these settings. For instance, if you have enabled may-insert-breakpoints but disabled may-write-memory, then breakpoints that work by writing trap instructions into the code stream will still not be able to be placed.

set observer on

set observer off

When set to on, this disables all the permission variables below (except for insert-fast-tracepoints), plus enables non-stop debugging. Setting this to off switches back to normal debugging, though remaining in non-stop mode.

show observer

Show whether observer mode is on or off.

set may-write-registers on

set may-write-registers off

This controls whether GDB will attempt to alter the values of registers, such as with assignment expressions in print, or the jump command. It defaults to on.

show may-write-registers

Show the current permission to write registers.

set may-write-memory on

set may-write-memory off

This controls whether GDB will attempt to alter the contents of memory, such as with assignment expressions in print. It defaults to on.

show may-write-memory

Show the current permission to write memory.

set may-insert-breakpoints on

set may-insert-breakpoints off

This controls whether GDB will attempt to insert breakpoints. This affects all breakpoints, including internal breakpoints defined by GDB. It defaults to on.

show may-insert-breakpoints

Show the current permission to insert breakpoints.

set may-insert-tracepoints on

set may-insert-tracepoints off

This controls whether GDB will attempt to insert (regular) tracepoints at the beginning of a tracing experiment. It affects only non-fast tracepoints, fast tracepoints being under the control of may-insert-fast-tracepoints. It defaults to on.

show may-insert-tracepoints

Show the current permission to insert tracepoints.

set may-insert-fast-tracepoints on

set may-insert-fast-tracepoints off

This controls whether GDB will attempt to insert fast tracepoints at the beginning of a tracing experiment. It affects only fast tracepoints, regular (non-fast) tracepoints being under the control of may-insert-tracepoints. It defaults to on.

show may-insert-fast-tracepoints

Show the current permission to insert fast tracepoints.

set may-interrupt on

set may-interrupt off

This controls whether GDB will attempt to interrupt or stop program execution. When this variable is off, the interrupt command will have no effect, nor will Ctrl-c. It defaults to on.

show may-interrupt

Show the current permission to interrupt or stop the program.