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KADB(4) FreeBSD Kernel Interfaces Manual KADB(4) NAME kdb - kernel debugging facility SYNOPSIS options KADB DESCRIPTION Kdb is a debugging facility for the kernel based on adb(1). Kdb may be used to symbolically examine and modify memory locations, set breakpoints, and single step the system. Several boot time options are used in conjunction with the debugger. To "enable" the debugger, the system must be booted with the RB_KDB flag (0x40) specified in the boothowto register. When the debugger is enabled the system will read in and initialize the symbol table from the booted system. If the RB_HALT flag (0x08) is also specified, the system will enter the debugger at the earliest possible time to allow breakpoints to be set before the system starts operation. From that point on, if the RB_NOSYNC flag (0x04) is set, typing `^[k', `^[K', or `^[^K' at the console causes a trap into the debugger. Kdb supports most of the adb command language. The output formats `f', `F', `Y', are not supported. The address space maps do not exist, thus the `m', `m', and `m' commands do not exist. Shell escapes and command files are not supported. The `r' and `k' commands make no sense and are not recognized. Finally, the signal arguments to the continue and single step commands are ignored. NOTES Kdb normally runs at a priority level below the interrupt level of the clock and all devices; the level of the highest priority software interrupt. If the debugger is entered on the kernel's per-process stack at an ipl below its normal operating level it automatically switches to the interrupt stack to avoid potential overflow of the kernel stack. Should the debugger operate on the kernel stack the message `(on kernel stack)' will be printed on entry. Note also that because kdb uses input from the console to force entry to the debugger it may not be possible to force entry if the system hangs at a priority level higher than the console receiver interrupt. SEE ALSO adb(1) HISTORY The kdb debugging facility currently under development. FreeBSD 14.1-RELEASE-p8 March 28, 1991 FreeBSD 14.1-RELEASE-p8