diff --git a/Makefile b/Makefile
index a3446b00..db9178f4 100644
--- a/Makefile
+++ b/Makefile
@@ -4,15 +4,18 @@ Q := @
 endif
 
 PC_HOSTED =
+NO_LIBOPENCM3 =
 ifeq ($(PROBE_HOST), libftdi)
 	PC_HOSTED = true
+	NO_LIBOPENCM3 = true
 endif
 ifeq ($(PROBE_HOST), pc-stlinkv2)
 	PC_HOSTED = true
+	NO_LIBOPENCM3 = true
 endif
 
 all:
-ifndef 	PC_HOSTED
+ifndef NO_LIBOPENCM3
 	$(Q)if [ ! -f libopencm3/Makefile ]; then \
 		echo "Initialising git submodules..." ;\
 		git submodule init ;\
@@ -23,7 +26,7 @@ endif
 	$(Q)$(MAKE) $(MFLAGS) -C src
 
 clean:
-ifndef 	PC_HOSTED
+ifndef NO_LIBOPENCM3
 	$(Q)$(MAKE) $(MFLAGS) -C libopencm3 $@
 endif
 	$(Q)$(MAKE) $(MFLAGS) -C src $@
diff --git a/src/Makefile b/src/Makefile
index 72132449..05f032e0 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -8,12 +8,9 @@ MAKEFLAGS += --no-print-dir
 Q := @
 endif
 
-OPT_FLAGS ?= -O2
-
 CFLAGS += -Wall -Wextra -Werror -Wno-char-subscripts -Wno-cast-function-type \
-	$(OPT_FLAGS) -std=gnu99 -g3 -MD \
+	-std=gnu99 -g3 -MD \
 	-I. -Iinclude -Iplatforms/common -I$(PLATFORM_DIR)
-LDFLAGS += $(OPT_FLAGS)
 
 ifeq ($(ENABLE_DEBUG), 1)
 CFLAGS += -DENABLE_DEBUG
@@ -60,6 +57,10 @@ SRC =			\
 
 include $(PLATFORM_DIR)/Makefile.inc
 
+OPT_FLAGS ?= -O2
+CFLAGS += $(OPT_FLAGS)
+LDFLAGS += $(OPT_FLAGS)
+
 ifndef TARGET
 TARGET=blackmagic
 endif
@@ -72,7 +73,7 @@ ifndef OWN_HL
 SRC += jtag_scan.c jtagtap.c swdptap.c
 endif
 
-OBJ = $(SRC:.c=.o)
+OBJ = $(patsubst %.S,%.o,$(patsubst %.c,%.o,$(SRC)))
 
 $(TARGET): include/version.h $(OBJ)
 	@echo "  LD      $@"
@@ -82,6 +83,10 @@ $(TARGET): include/version.h $(OBJ)
 	@echo "  CC      $<"
 	$(Q)$(CC) $(CFLAGS) -c $< -o $@
 
+%.o:	%.S
+	@echo "  AS      $<"
+	$(Q)$(CC) $(CFLAGS) -c $< -o $@
+
 %.bin:	%
 	@echo "  OBJCOPY $@"
 	$(Q)$(OBJCOPY) -O binary $^ $@
diff --git a/src/gdb_packet.c b/src/gdb_packet.c
index f738996a..0396e0d3 100644
--- a/src/gdb_packet.c
+++ b/src/gdb_packet.c
@@ -120,7 +120,7 @@ void gdb_putpacket(const char *packet, int size)
 			}
 		}
 		gdb_if_putchar('#', 0);
-		sprintf(xmit_csum, "%02X", csum);
+		snprintf(xmit_csum, sizeof(xmit_csum), "%02X", csum);
 		gdb_if_putchar(xmit_csum[0], 0);
 		gdb_if_putchar(xmit_csum[1], 1);
 #ifdef DEBUG_GDBPACKET
diff --git a/src/include/gdb_if.h b/src/include/gdb_if.h
index d2ad2439..1dc9e28d 100644
--- a/src/include/gdb_if.h
+++ b/src/include/gdb_if.h
@@ -21,7 +21,7 @@
 #ifndef __GDB_IF_H
 #define __GDB_IF_H
 
-#if !defined(PC_HOSTED)
+#if !defined(NO_LIBOPENCM3)
 #include <libopencm3/usb/usbd.h>
 void gdb_usb_out_cb(usbd_device *dev, uint8_t ep);
 #endif
diff --git a/src/platforms/libftdi/Makefile.inc b/src/platforms/libftdi/Makefile.inc
index 06c07d76..0ddabe89 100644
--- a/src/platforms/libftdi/Makefile.inc
+++ b/src/platforms/libftdi/Makefile.inc
@@ -1,5 +1,5 @@
 SYS = $(shell $(CC) -dumpmachine)
-CFLAGS += -DPC_HOSTED -DENABLE_DEBUG
+CFLAGS += -DPC_HOSTED -DNO_LIBOPENCM3 -DENABLE_DEBUG
 LDFLAGS += -lftdi1
 ifneq (, $(findstring mingw, $(SYS)))
 LDFLAGS +=  -lusb-1.0 -lws2_32
diff --git a/src/platforms/pc-stlinkv2/Makefile.inc b/src/platforms/pc-stlinkv2/Makefile.inc
index 53ec16a1..8762885d 100644
--- a/src/platforms/pc-stlinkv2/Makefile.inc
+++ b/src/platforms/pc-stlinkv2/Makefile.inc
@@ -1,6 +1,6 @@
 TARGET=blackmagic_stlinkv2
 SYS = $(shell $(CC) -dumpmachine)
-CFLAGS += -DPC_HOSTED  -DSTLINKV2 -DJTAG_HL -DENABLE_DEBUG
+CFLAGS += -DPC_HOSTED -DNO_LIBOPENCM3 -DSTLINKV2 -DJTAG_HL -DENABLE_DEBUG
 CFLAGS +=-I ./target
 LDFLAGS += -lusb-1.0
 ifneq (, $(findstring mingw, $(SYS)))
diff --git a/src/target/efm32.c b/src/target/efm32.c
index fff186ba..4405d99a 100644
--- a/src/target/efm32.c
+++ b/src/target/efm32.c
@@ -611,7 +611,7 @@ bool efm32_probe(target *t)
 	uint32_t ram_size   = ram_kib   * 0x400;
 	uint32_t flash_page_size = device->flash_page_size;
 
-	sprintf(variant_string, "%c\b%c\b%s %d F%d %s",
+	snprintf(variant_string, sizeof(variant_string), "%c\b%c\b%s %d F%d %s",
 			di_version + 48, (uint8_t)device_index + 32,
 			device->name, part_number, flash_kib, device->description);
 
diff --git a/src/target/samd.c b/src/target/samd.c
index 588ca83c..3117f2ae 100644
--- a/src/target/samd.c
+++ b/src/target/samd.c
@@ -364,7 +364,7 @@ static void samd_add_flash(target *t, uint32_t addr, size_t length)
 	target_add_flash(t, f);
 }
 
-char variant_string[40];
+char variant_string[60];
 bool samd_probe(target *t)
 {
 	uint32_t cid = samd_read_cid(t);
@@ -390,15 +390,15 @@ bool samd_probe(target *t)
 
 	/* Part String */
 	if (protected) {
-		sprintf(variant_string,
-		        "Atmel SAMD%d%c%dA%s (rev %c) (PROT=1)",
-		        samd.series, samd.pin, samd.mem,
-		        samd.package, samd.revision);
+		snprintf(variant_string, sizeof(variant_string),
+		         "Atmel SAMD%d%c%dA%s (rev %c) (PROT=1)",
+		         samd.series, samd.pin, samd.mem,
+		         samd.package, samd.revision);
 	} else {
-		sprintf(variant_string,
-		        "Atmel SAMD%d%c%dA%s (rev %c)",
-		        samd.series, samd.pin, samd.mem,
-		        samd.package, samd.revision);
+		snprintf(variant_string, sizeof(variant_string),
+		         "Atmel SAMD%d%c%dA%s (rev %c)",
+		         samd.series, samd.pin, samd.mem,
+		         samd.package, samd.revision);
 	}
 
 	/* Setup Target */