Reliably enable debug exceptions on all CPUs.

Previously, debug exceptions were only enabled on the boot CPU if
DDB was enabled in the dbg_monitor_init() function.  APs also called
this function, but since mp_machdep.c doesn't include opt_ddb.h, the
APs ended up calling an empty stub defined in <machine/debug_monitor.h>
instead of the real function.  Also, if DDB was not enabled in the kernel,
the boot CPU would not enable debug exceptions.

Fix this by adding a new dbg_init() function that always clears the OS
lock to enable debug exceptions which the boot CPU and the APs call.
This function also calls dbg_monitor_init() to enable hardware breakpoints
from DDB on all CPUs if DDB is enabled.  Eventually base support for
hardware breakpoints/watchpoints will need to move out of the DDB-only
debug_monitor.c for use by userland debuggers.

Reviewed by:	andrew
Differential Revision:	https://reviews.freebsd.org/D12001

3 files changed, 16 insertions, 7 deletions

diff --git a/sys/arm64/arm64/debug_monitor.c b/sys/arm64/arm64/debug_monitor.c
index 4d458fc58060..4f0e29daadfb 100644
--- a/sys/arm64/arm64/debug_monitor.c
+++ b/sys/arm64/arm64/debug_monitor.c
@@ -453,15 +453,12 @@ dbg_monitor_init(void)
 {
 	u_int i;
 
-	/* Clear OS lock */
-	WRITE_SPECIALREG(OSLAR_EL1, 0);
-
 	/* Find out many breakpoints and watchpoints we can use */
 	dbg_watchpoint_num = ((READ_SPECIALREG(ID_AA64DFR0_EL1) >> 20) & 0xf) + 1;
 	dbg_breakpoint_num = ((READ_SPECIALREG(ID_AA64DFR0_EL1) >> 12) & 0xf) + 1;
 
 	if (bootverbose && PCPU_GET(cpuid) == 0) {
-		db_printf("%d watchpoints and %d breakpoints supported\n",
+		printf("%d watchpoints and %d breakpoints supported\n",
 		    dbg_watchpoint_num, dbg_breakpoint_num);
 	}
 
diff --git a/sys/arm64/arm64/machdep.c b/sys/arm64/arm64/machdep.c
index 300498f608f1..5e658d3a041b 100644
--- a/sys/arm64/arm64/machdep.c
+++ b/sys/arm64/arm64/machdep.c
@@ -1051,13 +1051,26 @@ initarm(struct arm64_bootparams *abp)
 	mutex_init();
 	init_param2(physmem);
 
-	dbg_monitor_init();
+	dbg_init();
 	kdb_init();
 	pan_enable();
 
 	early_boot = 0;
 }
 
+void
+dbg_init(void)
+{
+
+	/* Clear OS lock */
+	WRITE_SPECIALREG(OSLAR_EL1, 0);
+
+	/* This permits DDB to use debug registers for watchpoints. */
+	dbg_monitor_init();
+
+	/* TODO: Eventually will need to initialize debug registers here. */
+}
+
 #ifdef DDB
 #include <ddb/ddb.h>
 
diff --git a/sys/arm64/arm64/mp_machdep.c b/sys/arm64/arm64/mp_machdep.c
index c7e8a8df1e9d..ab1171c777d3 100644
--- a/sys/arm64/arm64/mp_machdep.c
+++ b/sys/arm64/arm64/mp_machdep.c
@@ -52,7 +52,6 @@ __FBSDID("$FreeBSD$");
 #include <vm/vm_extern.h>
 #include <vm/vm_kern.h>
 
-#include <machine/debug_monitor.h>
 #include <machine/machdep.h>
 #include <machine/intr.h>
 #include <machine/smp.h>
@@ -272,7 +271,7 @@ init_secondary(uint64_t cpu)
 	vfp_init();
 #endif
 
-	dbg_monitor_init();
+	dbg_init();
 	pan_enable();
 
 	/* Enable interrupts */