arm64: gdb(4) machine-dependent bits

Everything required for remote kernel debugging over a serial
connection. For FDT-based systems, a debug port can be specified by
setting hw.fdt.dbgport to the desired device tree node in loader.conf.
For example, hw.fdt.dbgport="uart1", or
hw.fdt.dbgport="serial@ff1a0000".

Looks good:	emaste
Tested by:	rwatson
MFC after:	2 weeks
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D27727

sys/arm64/arm64/gdb_machdep.c

@@ -0,0 +1,112 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+ *
+ * Copyright (c) 2020 The FreeBSD Foundation
+ *
+ * This software was developed by Mitchell Horne under sponsorship from
+ * the FreeBSD Foundation.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/param.h>
+#include <sys/systm.h>
+#include <sys/kdb.h>
+#include <sys/kernel.h>
+#include <sys/proc.h>
+#include <sys/signal.h>
+
+#include <machine/armreg.h>
+#include <machine/frame.h>
+#include <machine/gdb_machdep.h>
+#include <machine/pcb.h>
+
+#include <gdb/gdb.h>
+
+void *
+gdb_cpu_getreg(int regnum, size_t *regsz)
+{
+
+	*regsz = gdb_cpu_regsz(regnum);
+
+	if (kdb_thread == curthread) {
+		switch (regnum) {
+		case GDB_REG_LR:   return (&kdb_frame->tf_lr);
+		case GDB_REG_SP:   return (&kdb_frame->tf_sp);
+		case GDB_REG_PC:   return (&kdb_frame->tf_elr);
+		case GDB_REG_CSPR: return (&kdb_frame->tf_spsr);
+		}
+	}
+	switch (regnum) {
+	case GDB_REG_SP: return (&kdb_thrctx->pcb_sp);
+	case GDB_REG_PC: /* FALLTHROUGH */
+	case GDB_REG_LR: return (&kdb_thrctx->pcb_lr);
+	default:
+		if (regnum >= GDB_REG_X0 && regnum <= GDB_REG_X29)
+			return (&kdb_thrctx->pcb_x[regnum]);
+		break;
+	}
+
+	return (NULL);
+}
+
+void
+gdb_cpu_setreg(int regnum, void *val)
+{
+	register_t regval = *(register_t *)val;
+
+	/* For curthread, keep the pcb and trapframe in sync. */
+	if (kdb_thread == curthread) {
+		switch (regnum) {
+		case GDB_REG_PC: kdb_frame->tf_elr = regval; break;
+		case GDB_REG_SP: kdb_frame->tf_sp  = regval; break;
+		default:
+			if (regnum >= GDB_REG_X0 && regnum <= GDB_REG_X29) {
+				kdb_frame->tf_x[regnum] = regval;
+			}
+			break;
+		}
+	}
+	switch (regnum) {
+	case GDB_REG_PC: /* FALLTHROUGH */
+	case GDB_REG_LR: kdb_thrctx->pcb_lr = regval; break;
+	case GDB_REG_SP: kdb_thrctx->pcb_sp = regval; break;
+	default:
+		if (regnum >= GDB_REG_X0 && regnum <= GDB_REG_X29) {
+			kdb_thrctx->pcb_x[regnum] = regval;
+		}
+		break;
+	}
+}
+
+int
+gdb_cpu_signal(int type, int code __unused)
+{
+
+	switch (type) {
+	case EXCP_WATCHPT_EL1:
+	case EXCP_SOFTSTP_EL1:
+	case EXCP_BRK:
+		return (SIGTRAP);
+	}
+	return (SIGEMT);
+}

sys/arm64/conf/GENERIC

@@ -87,7 +87,7 @@ options 	KDB			# Enable kernel debugger support.
 options 	KDB_TRACE		# Print a stack trace for a panic.
 # For full debugger support use (turn off in stable branch):
 options 	DDB			# Support DDB.
-#options 	GDB			# Support remote GDB.
+options 	GDB			# Support remote GDB.
 options 	DEADLKRES		# Enable the deadlock resolver
 options 	INVARIANTS		# Enable calls of extra sanity checking
 options 	INVARIANT_SUPPORT	# Extra sanity checks of internal structures, required by INVARIANTS

sys/arm64/include/gdb_machdep.h

@@ -0,0 +1,81 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+ *
+ * Copyright (c) 2020 The FreeBSD Foundation
+ *
+ * This software was developed by Mitchell Horne under sponsorship from
+ * the FreeBSD Foundation.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifndef _MACHINE_GDB_MACHDEP_H_
+#define	_MACHINE_GDB_MACHDEP_H_
+
+#define	GDB_BUFSZ	4096
+#define	GDB_NREGS	68
+#define	GDB_REG_X0	0
+#define	GDB_REG_X29	29
+#define	GDB_REG_LR	30
+#define	GDB_REG_SP	31
+#define	GDB_REG_PC	32
+#define	GDB_REG_CSPR	33
+#define	GDB_REG_V0	34
+#define	GDB_REG_V31	65
+#define	GDB_REG_FPSR	66
+#define	GDB_REG_FPCR	67
+_Static_assert(GDB_BUFSZ >= (GDB_NREGS * 16), "buffer fits 'g' regs");
+
+static __inline size_t
+gdb_cpu_regsz(int regnum)
+{
+	if (regnum == GDB_REG_CSPR || regnum == GDB_REG_FPSR ||
+	    regnum == GDB_REG_FPCR)
+		return (4);
+	else if (regnum >= GDB_REG_V0 && regnum <= GDB_REG_V31)
+		return (16);
+
+	return (8);
+}
+
+static __inline int
+gdb_cpu_query(void)
+{
+	return (0);
+}
+
+static __inline void *
+gdb_begin_write(void)
+{
+	return (NULL);
+}
+
+static __inline void
+gdb_end_write(void *arg __unused)
+{
+}
+
+void *gdb_cpu_getreg(int, size_t *);
+void gdb_cpu_setreg(int, void *);
+int gdb_cpu_signal(int, int);
+
+#endif /* !_MACHINE_GDB_MACHDEP_H_ */

sys/conf/files.arm64

@@ -168,6 +168,7 @@ arm64/arm64/elf32_machdep.c	optional	compat_freebsd32
 arm64/arm64/elf_machdep.c	standard
 arm64/arm64/exception.S		standard
 arm64/arm64/freebsd32_machdep.c	optional	compat_freebsd32
+arm64/arm64/gdb_machdep.c	optional	gdb
 arm64/arm64/gicv3_its.c		optional	intrng fdt
 arm64/arm64/gic_v3.c		standard
 arm64/arm64/gic_v3_acpi.c	optional	acpi