MN10300: gdbstub: Restrict single-stepping to non-preemptable non-SMP configs

Restrict single-stepping through the kernel using gdbstub to non-preemptable
non-SMP configs as gdbstub has to do software single-stepping by means of
temporary breakpoints.  Hardware single-stepping is unavailable as Panasonic
have not sufficiently documented the interface to it.

Software single-stepping through preemptable or SMP kernels runs into problems
as it makes it much more likely that the wrong thread will hit the temporary
breakpoints.  It seems impractical to work around the problem for the most
part.  It could be possible to make a UP preemptable kernel switch temporary
breakpoints in and out in switch_to().

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/arch/mn10300/Kconfig.debug b/arch/mn10300/Kconfig.debug
index ce83c74..a1b8620 100644
--- a/arch/mn10300/Kconfig.debug
+++ b/arch/mn10300/Kconfig.debug
@@ -54,6 +54,14 @@ config GDBSTUB_IMMEDIATE
 	  possible, leaving the program counter at the beginning of
 	  start_kernel() in init/main.c.
 
+config GDBSTUB_ALLOW_SINGLE_STEP
+	bool "Allow software single-stepping in GDB stub"
+	depends on GDBSTUB && !SMP && !PREEMPT
+	help
+	  Allow GDB stub to perform software single-stepping through the
+	  kernel.  This doesn't work very well on SMP or preemptible kernels as
+	  it uses temporary breakpoints to emulate single-stepping.
+
 config GDB_CONSOLE
 	bool "Console output to GDB"
 	depends on GDBSTUB