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Using kgdb requires at least some level of architecture-level initialization. If nothing else, it relies on the architecture to pass breakpoints / crashes onto kgdb. On some architectures this all works super early, specifically it starts working at some point in time before Linux parses early_params's. On other architectures it doesn't. A survey of a few platforms: a) x86: Presumably it all works early since "ekgdboc" is documented to work here. b) arm64: Catching crashes works; with a simple patch breakpoints can also be made to work. c) arm: Nothing in kgdb works until paging_init() -> devicemaps_init() -> early_trap_init() Let's be conservative and, by default, process "kgdbwait" (which tells the kernel to drop into the debugger ASAP at boot) a bit later at dbg_late_init() time. If an architecture has tested it and wants to re-enable super early debugging, they can select the ARCH_HAS_EARLY_DEBUG KConfig option. We'll do this for x86 to start. It should be noted that dbg_late_init() is still called quite early in the system. Note that this patch doesn't affect when kgdb runs its init. If kgdb is set to initialize early it will still initialize when parsing early_param's. This patch _only_ inhibits the initial breakpoint from "kgdbwait". This means: * Without any extra patches arm64 platforms will at least catch crashes after kgdb inits. * arm platforms will catch crashes (and could handle a hardcoded kgdb_breakpoint()) any time after early_trap_init() runs, even before dbg_late_init(). Signed-off-by: Douglas Anderson <dianders@chromium.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Link: https://lore.kernel.org/r/20200507130644.v4.4.I3113aea1b08d8ce36dc3720209392ae8b815201b@changeid Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
146 lines
4.9 KiB
Plaintext
146 lines
4.9 KiB
Plaintext
# SPDX-License-Identifier: GPL-2.0-only
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config HAVE_ARCH_KGDB
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bool
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menuconfig KGDB
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bool "KGDB: kernel debugger"
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depends on HAVE_ARCH_KGDB
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depends on DEBUG_KERNEL
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help
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If you say Y here, it will be possible to remotely debug the
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kernel using gdb. It is recommended but not required, that
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you also turn on the kernel config option
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CONFIG_FRAME_POINTER to aid in producing more reliable stack
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backtraces in the external debugger. Documentation of
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kernel debugger is available at http://kgdb.sourceforge.net
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as well as in Documentation/dev-tools/kgdb.rst. If
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unsure, say N.
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if KGDB
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config KGDB_SERIAL_CONSOLE
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tristate "KGDB: use kgdb over the serial console"
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select CONSOLE_POLL
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select MAGIC_SYSRQ
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depends on TTY && HW_CONSOLE
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default y
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help
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Share a serial console with kgdb. Sysrq-g must be used
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to break in initially.
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config KGDB_TESTS
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bool "KGDB: internal test suite"
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default n
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help
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This is a kgdb I/O module specifically designed to test
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kgdb's internal functions. This kgdb I/O module is
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intended to for the development of new kgdb stubs
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as well as regression testing the kgdb internals.
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See the drivers/misc/kgdbts.c for the details about
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the tests. The most basic of this I/O module is to boot
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a kernel boot arguments "kgdbwait kgdbts=V1F100"
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config KGDB_TESTS_ON_BOOT
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bool "KGDB: Run tests on boot"
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depends on KGDB_TESTS
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default n
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help
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Run the kgdb tests on boot up automatically without the need
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to pass in a kernel parameter
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config KGDB_TESTS_BOOT_STRING
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string "KGDB: which internal kgdb tests to run"
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depends on KGDB_TESTS_ON_BOOT
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default "V1F100"
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help
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This is the command string to send the kgdb test suite on
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boot. See the drivers/misc/kgdbts.c for detailed
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information about other strings you could use beyond the
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default of V1F100.
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config KGDB_LOW_LEVEL_TRAP
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bool "KGDB: Allow debugging with traps in notifiers"
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depends on X86 || MIPS
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default n
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help
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This will add an extra call back to kgdb for the breakpoint
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exception handler which will allow kgdb to step through a
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notify handler.
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config KGDB_KDB
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bool "KGDB_KDB: include kdb frontend for kgdb"
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default n
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help
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KDB frontend for kernel
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config KDB_DEFAULT_ENABLE
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hex "KDB: Select kdb command functions to be enabled by default"
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depends on KGDB_KDB
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default 0x1
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help
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Specifiers which kdb commands are enabled by default. This may
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be set to 1 or 0 to enable all commands or disable almost all
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commands.
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Alternatively the following bitmask applies:
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0x0002 - allow arbitrary reads from memory and symbol lookup
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0x0004 - allow arbitrary writes to memory
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0x0008 - allow current register state to be inspected
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0x0010 - allow current register state to be modified
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0x0020 - allow passive inspection (backtrace, process list, lsmod)
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0x0040 - allow flow control management (breakpoint, single step)
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0x0080 - enable signalling of processes
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0x0100 - allow machine to be rebooted
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The config option merely sets the default at boot time. Both
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issuing 'echo X > /sys/module/kdb/parameters/cmd_enable' or
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setting with kdb.cmd_enable=X kernel command line option will
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override the default settings.
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config KDB_KEYBOARD
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bool "KGDB_KDB: keyboard as input device"
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depends on VT && KGDB_KDB
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default n
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help
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KDB can use a PS/2 type keyboard for an input device
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config KDB_CONTINUE_CATASTROPHIC
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int "KDB: continue after catastrophic errors"
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depends on KGDB_KDB
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default "0"
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help
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This integer controls the behaviour of kdb when the kernel gets a
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catastrophic error, i.e. for a panic or oops.
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When KDB is active and a catastrophic error occurs, nothing extra
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will happen until you type 'go'.
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CONFIG_KDB_CONTINUE_CATASTROPHIC == 0 (default). The first time
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you type 'go', you will be warned by kdb. The secend time you type
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'go', KDB tries to continue. No guarantees that the
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kernel is still usable in this situation.
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CONFIG_KDB_CONTINUE_CATASTROPHIC == 1. KDB tries to continue.
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No guarantees that the kernel is still usable in this situation.
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CONFIG_KDB_CONTINUE_CATASTROPHIC == 2. KDB forces a reboot.
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If you are not sure, say 0.
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config ARCH_HAS_EARLY_DEBUG
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bool
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default n
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help
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If an architecture can definitely handle entering the debugger
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when early_param's are parsed then it select this config.
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Otherwise, if "kgdbwait" is passed on the kernel command line it
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won't actually be processed until dbg_late_init() just after the
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call to kgdb_arch_late() is made.
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NOTE: Even if this isn't selected by an architecture we will
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still try to register kgdb to handle breakpoints and crashes
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when early_param's are parsed, we just won't act on the
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"kgdbwait" parameter until dbg_late_init(). If you get a
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crash and try to drop into kgdb somewhere between these two
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places you might or might not end up being able to use kgdb
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depending on exactly how far along the architecture has initted.
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endif # KGDB
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