gdb: report specific stop reason for watchpoints

The remote protocol allows for implementations to report more specific
reasons for the break in execution back to the client [1]. This is
entirely optional, so it is only implemented for amd64, arm64, and i386
at the moment.

[1] https://sourceware.org/gdb/current/onlinedocs/gdb/Stop-Reply-Packets.html

Reviewed by:	jhb
MFC after:	3 weeks
Sponsored by:	NetApp, Inc.
Sponsored by:	Klara, Inc.
NetApp PR:	51
Differential Revision:	https://reviews.freebsd.org/D29174

10 files changed, 108 insertions, 3 deletions

diff --git a/sys/amd64/amd64/gdb_machdep.c b/sys/amd64/amd64/gdb_machdep.c
index 610096e1355d..176c770a3731 100644
--- a/sys/amd64/amd64/gdb_machdep.c
+++ b/sys/amd64/amd64/gdb_machdep.c
@@ -49,6 +49,7 @@ __FBSDID("$FreeBSD$");
 #include <machine/endian.h>
 
 #include <gdb/gdb.h>
+#include <gdb/gdb_int.h>
 
 void *
 gdb_cpu_getreg(int regnum, size_t *regsz)
@@ -152,6 +153,40 @@ gdb_cpu_signal(int type, int code)
 	return (SIGEMT);
 }
 
+void
+gdb_cpu_stop_reason(int type, int code)
+{
+	uintmax_t val;
+
+	val = 0;
+	if (type == T_TRCTRAP) {
+		/* NB: 'code' contains the value of dr6 at the trap. */
+		if ((code & DBREG_DR6_B(0)) != 0) {
+			val = rdr0();
+		}
+		if ((code & DBREG_DR6_B(1)) != 0) {
+			val = rdr1();
+		}
+		if ((code & DBREG_DR6_B(2)) != 0) {
+			val = rdr2();
+		}
+		if ((code & DBREG_DR6_B(3)) != 0) {
+			val = rdr3();
+		}
+
+		/*
+		 * TODO: validate the bits in DR7 to differentiate between a
+		 * watchpoint trap and a hardware breakpoint trap (currently
+		 * unsupported).
+		 */
+		if (val != 0) {
+			gdb_tx_str("watch:");
+			gdb_tx_varhex(val);
+			gdb_tx_char(';');
+		}
+	}
+}
+
 void *
 gdb_begin_write(void)
 {
diff --git a/sys/amd64/include/gdb_machdep.h b/sys/amd64/include/gdb_machdep.h
index 459d4f17e9d1..4379b8a74709 100644
--- a/sys/amd64/include/gdb_machdep.h
+++ b/sys/amd64/include/gdb_machdep.h
@@ -72,5 +72,6 @@ void *gdb_cpu_getreg(int, size_t *);
 void gdb_cpu_setreg(int, void *);
 int gdb_cpu_signal(int, int);
 void gdb_end_write(void *);
+void gdb_cpu_stop_reason(int, int);
 
 #endif /* !_MACHINE_GDB_MACHDEP_H_ */
diff --git a/sys/arm/include/gdb_machdep.h b/sys/arm/include/gdb_machdep.h
index 017025253bd5..5190c2a4097e 100644
--- a/sys/arm/include/gdb_machdep.h
+++ b/sys/arm/include/gdb_machdep.h
@@ -66,6 +66,12 @@ gdb_end_write(void *arg __unused)
 
 }
 
+static __inline void
+gdb_cpu_stop_reason(int type __unused, int code __unused)
+{
+
+}
+
 void *gdb_cpu_getreg(int, size_t *);
 void gdb_cpu_setreg(int, void *);
 int gdb_cpu_signal(int, int);
diff --git a/sys/arm64/arm64/gdb_machdep.c b/sys/arm64/arm64/gdb_machdep.c
index dc0a7eeba692..b27e1edb3d7f 100644
--- a/sys/arm64/arm64/gdb_machdep.c
+++ b/sys/arm64/arm64/gdb_machdep.c
@@ -41,6 +41,7 @@
 #include <machine/pcb.h>
 
 #include <gdb/gdb.h>
+#include <gdb/gdb_int.h>
 
 void *
 gdb_cpu_getreg(int regnum, size_t *regsz)
@@ -110,3 +111,14 @@ gdb_cpu_signal(int type, int code __unused)
 	}
 	return (SIGEMT);
 }
+
+void
+gdb_cpu_stop_reason(int type, int code __unused)
+{
+
+	if (type == EXCP_WATCHPT_EL1) {
+		gdb_tx_str("watch:");
+		gdb_tx_varhex((uintmax_t)READ_SPECIALREG(far_el1));
+		gdb_tx_char(';');
+	}
+}
diff --git a/sys/arm64/include/gdb_machdep.h b/sys/arm64/include/gdb_machdep.h
index 755c5d1657c0..17b46edd1a27 100644
--- a/sys/arm64/include/gdb_machdep.h
+++ b/sys/arm64/include/gdb_machdep.h
@@ -77,5 +77,6 @@ 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);
+void gdb_cpu_stop_reason(int, int);
 
 #endif /* !_MACHINE_GDB_MACHDEP_H_ */
diff --git a/sys/gdb/gdb_main.c b/sys/gdb/gdb_main.c
index a4469fdf4997..c5e4ba608f29 100644
--- a/sys/gdb/gdb_main.c
+++ b/sys/gdb/gdb_main.c
@@ -741,8 +741,9 @@ gdb_trap(int type, int code)
 	gdb_tx_char(':');
 	gdb_tx_reg(GDB_REG_PC);
 	gdb_tx_char(';');
+	gdb_cpu_stop_reason(type, code);
 	gdb_tx_str("thread:");
-	gdb_tx_varhex((long)kdb_thread->td_tid);
+	gdb_tx_varhex((uintmax_t)kdb_thread->td_tid);
 	gdb_tx_char(';');
 	gdb_tx_end();			/* XXX check error condition. */
 
diff --git a/sys/i386/i386/gdb_machdep.c b/sys/i386/i386/gdb_machdep.c
index fd522309dbb2..549c6de7ba1b 100644
--- a/sys/i386/i386/gdb_machdep.c
+++ b/sys/i386/i386/gdb_machdep.c
@@ -36,13 +36,15 @@ __FBSDID("$FreeBSD$");
 #include <sys/proc.h>
 #include <sys/signal.h>
 
+#include <machine/endian.h>
+#include <machine/frame.h>
 #include <machine/gdb_machdep.h>
 #include <machine/pcb.h>
+#include <machine/reg.h>
 #include <machine/trap.h>
-#include <machine/frame.h>
-#include <machine/endian.h>
 
 #include <gdb/gdb.h>
+#include <gdb/gdb_int.h>
 
 void *
 gdb_cpu_getreg(int regnum, size_t *regsz)
@@ -114,3 +116,37 @@ gdb_cpu_signal(int type, int code)
 	}
 	return (SIGEMT);
 }
+
+void
+gdb_cpu_stop_reason(int type, int code)
+{
+	uintmax_t val;
+
+	val = 0;
+	if (type == T_TRCTRAP) {
+		/* NB: 'code' contains the value of dr6 at the trap. */
+		if ((code & DBREG_DR6_B(0)) != 0) {
+			val = rdr0();
+		}
+		if ((code & DBREG_DR6_B(1)) != 0) {
+			val = rdr1();
+		}
+		if ((code & DBREG_DR6_B(2)) != 0) {
+			val = rdr2();
+		}
+		if ((code & DBREG_DR6_B(3)) != 0) {
+			val = rdr3();
+		}
+
+		/*
+		 * TODO: validate the bits in DR7 to differentiate between a
+		 * watchpoint trap and a hardware breakpoint trap (currently
+		 * unsupported).
+		 */
+		if (val != 0) {
+			gdb_tx_str("watch:");
+			gdb_tx_varhex(val);
+			gdb_tx_char(';');
+		}
+	}
+}
diff --git a/sys/i386/include/gdb_machdep.h b/sys/i386/include/gdb_machdep.h
index ef9500160be1..77eb70e2fb28 100644
--- a/sys/i386/include/gdb_machdep.h
+++ b/sys/i386/include/gdb_machdep.h
@@ -63,5 +63,6 @@ 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);
+void gdb_cpu_stop_reason(int, int);
 
 #endif /* !_MACHINE_GDB_MACHDEP_H_ */
diff --git a/sys/mips/include/gdb_machdep.h b/sys/mips/include/gdb_machdep.h
index 03378b760024..e8ff620edc88 100644
--- a/sys/mips/include/gdb_machdep.h
+++ b/sys/mips/include/gdb_machdep.h
@@ -64,6 +64,12 @@ gdb_end_write(void *arg __unused)
 
 }
 
+static __inline void
+gdb_cpu_stop_reason(int type __unused, int code __unused)
+{
+
+}
+
 void *gdb_cpu_getreg(int, size_t *);
 void gdb_cpu_setreg(int, void *);
 int gdb_cpu_signal(int, int);
diff --git a/sys/powerpc/include/gdb_machdep.h b/sys/powerpc/include/gdb_machdep.h
index 41a9ab1f4fa7..5edf4d96cb7c 100644
--- a/sys/powerpc/include/gdb_machdep.h
+++ b/sys/powerpc/include/gdb_machdep.h
@@ -128,6 +128,12 @@ gdb_end_write(void *arg __unused)
 
 }
 
+static __inline void
+gdb_cpu_stop_reason(int type __unused, int code __unused)
+{
+
+}
+
 void *gdb_cpu_getreg(int, size_t *);
 void gdb_cpu_setreg(int, void *);
 int gdb_cpu_signal(int, int);