Small static psk TLS 1.2 build for microchip

mplabx/small-psk-build/Makefile

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+# Set to @ if you want to suppress command echo
+CMD_ECHO =
+
+# Important directories
+BUILD_DIR = ./Build
+
+# Toolchain location and prefix
+TOOLCHAIN ?=
+
+# Tools selection
+CC = $(TOOLCHAIN)gcc
+AS = $(CC)
+LD = $(CC)
+AR = $(TOOLCHAIN)ar
+NM = $(TOOLCHAIN)nm
+OBJCOPY ?= $(TOOLCHAIN)objcopy
+OBJDUMP ?= $(TOOLCHAIN)objdump
+SIZE ?= $(TOOLCHAIN)size
+
+# Includes
+USER_SETTINGS_DIR ?= .
+INC = -I$(USER_SETTINGS_DIR) \
+      -I../..
+
+# Defines
+DEF = -DWOLFSSL_USER_SETTINGS -DWOLFSSL_GENSEED_FORTEST
+#DEF += -DUSE_LIBFUZZER
+#CFLAGS = -fsanitize=fuzzer,address -g
+
+# LD: generate map
+LDFLAGS += -Wl,-Map=$(BUILD_DIR)/$(BIN).map
+
+# LD: Entry point
+LDFLAGS += -Wl,-ereset_handler
+
+# Math lib (for DH)
+LIBS = -lm
+
+# Optimization level and place functions / data into separate sections to allow dead code removal
+CFLAGS += -Os -ffunction-sections -fdata-sections -fno-builtin
+# Remove unused sections and link time optimizations
+LDFLAGS += -Wl,--gc-sections -flto
+
+# Debugging
+#DBGFLAGS = -ggdb -g3
+CFLAGS += $(DBGFLAGS)
+LDFLAGS += $(DBGFLAGS)
+
+
+# FILES
+SRC_C += ../../wolfcrypt/src/aes.c
+SRC_C += ../../wolfcrypt/src/hmac.c
+SRC_C += ../../wolfcrypt/src/random.c
+SRC_C += ../../wolfcrypt/src/sha256.c
+SRC_C += ../../wolfcrypt/src/misc.c
+SRC_C += psk-ssl.c
+SRC_C += psk-tls.c
+SRC_C += example-client-psk.c
+
+
+FILENAMES_C = $(notdir $(SRC_C))
+FILENAMES_C := $(filter-out evp.c, $(FILENAMES_C))
+OBJS_C = $(addprefix $(BUILD_DIR)/, $(FILENAMES_C:.c=.o))
+vpath %.c $(dir $(SRC_C))
+
+APP = example-client-psk
+
+all: $(BUILD_DIR) $(BUILD_DIR)/$(APP)
+	@echo ""
+	$(CMD_ECHO) $(SIZE) $(BUILD_DIR)/$(APP)
+
+$(BUILD_DIR):
+	$(CMD_ECHO) mkdir -p $(BUILD_DIR)
+
+$(BUILD_DIR)/%.o: %.c
+	@echo "Compiling C file: $(notdir $<)"
+	$(CMD_ECHO) $(CC) $(CFLAGS) $(DEF) $(INC) -c -o $@ $<
+
+$(BUILD_DIR)/$(APP): $(OBJS_C)
+	@echo "Linking object files:"
+	$(CMD_ECHO) $(CC) $(CFLAGS) $(DEF) $(INC) -o $@ $(OBJS_C)
+
+
+clean:
+	rm -f $(BUILD_DIR)/*.o $(BUILD_DIR)/$(APP)
+

mplabx/small-psk-build/README.md

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+NOT intended for general use!
+
+Crafted for a specific static PSK build using an AES-CBC 128 cipher suite with
+TLS 1.2 client. When compiling with the Microchip toolchain additional source
+files consumed a small amount of DATA memory. psk-tls.c and psk-ssl.c are the
+combination of; src/ssl.c, src/tls.c, src/internal.c, src/keys.c, src/wolfio.c,
+and wolfcrypt/src/kdf.c. The code has then been trimmed for the specific use
+case and adjusted to flatten the call stack. The compiler used had a limit of
+around 32 function calls deep for the call stack. The linker used also was
+unable to effectivily trim out unused functions, hence a lot of the unused
+functions were removed in psk-tls.c and psk-ssl.c.
+
+To build the example client using the gcc compiler run `make` from this
+directory and then `./Build/example-client-psk`.