Fixed build errors with cross-clang compiler

Makefile

@@ -25,7 +25,12 @@ LIBS=
 SIGN_ALG=
 OBJCOPY_FLAGS=
 BIG_ENDIAN?=0
+USE_CLANG?=0
+ifeq ($(USE_CLANG),1)
+USE_GCC?=0
+else
 USE_GCC?=1
+endif
 USE_GCC_HEADLESS?=1
 FLASH_OTP_KEYSTORE?=0
 BOOTLOADER_PARTITION_SIZE?=$$(( $(WOLFBOOT_PARTITION_BOOT_ADDRESS) - $(ARCH_FLASH_OFFSET)))
@@ -180,7 +185,7 @@ CFLAGS+=$(WOLFPSA_CFLAGS)
 
 # Setup default optimizations (for GCC)
 ifeq ($(USE_GCC_HEADLESS),1)
-  CFLAGS+=-Wall -Wextra -Wno-main -ffreestanding -nostartfiles
+  CFLAGS+=-Wall -Wextra -Wno-main -ffreestanding
   CFLAGS+=-ffunction-sections -fdata-sections -fomit-frame-pointer
   # Allow unused parameters and functions
   CFLAGS+=-Wno-unused-parameter -Wno-unused-function

arch.mk

@@ -134,8 +134,14 @@ endif
 ifeq ($(ARCH),ARM)
   CROSS_COMPILE?=arm-none-eabi-
   CFLAGS+=-DARCH_ARM
-  CFLAGS+=-mthumb -mlittle-endian -mthumb-interwork
-  LDFLAGS+=-mthumb -mlittle-endian -mthumb-interwork
+  CFLAGS+=-mthumb -mlittle-endian
+  LDFLAGS+=-mthumb -mlittle-endian
+  ifeq ($(USE_GCC),1)
+    ifeq ($(findstring clang,$(notdir $(CC))),)
+    CFLAGS+=-mthumb-interwork
+    LDFLAGS+=-mthumb-interwork
+    endif
+  endif
 
   ## Target specific configuration
   ifeq ($(TARGET),samr21)
@@ -1216,6 +1222,29 @@ ifeq ($(TARGET),psoc6)
     endif
 endif
 
+ifeq ($(USE_CLANG),1)
+  ifneq ($(ARCH),ARM)
+    $(error USE_CLANG=1 is currently supported only for ARCH=ARM)
+  endif
+  CLANG?=clang
+  CLANG_GCC_NAME?=$(CROSS_COMPILE)gcc
+  CLANG_TARGET?=arm-none-eabi
+  CLANG_DRIVER:=$(CLANG) --target=$(CLANG_TARGET) -ccc-gcc-name $(CLANG_GCC_NAME)
+  CLANG_LIBC_A?=$(shell $(CLANG_GCC_NAME) -print-file-name=libc.a)
+  CLANG_NEWLIB_INCLUDE?=$(abspath $(dir $(CLANG_LIBC_A))/../include)
+
+  CC=$(CLANG_DRIVER)
+  LD=$(CLANG_DRIVER)
+  AS=$(CLANG_DRIVER)
+  AR=$(CROSS_COMPILE)ar
+  OBJCOPY?=$(CROSS_COMPILE)objcopy
+  SIZE=$(CROSS_COMPILE)size
+
+  CFLAGS+=-isystem $(CLANG_NEWLIB_INCLUDE)
+  CFLAGS+=-DWOLFSSL_NO_ATOMIC -DWOLFSSL_NO_ATOMICS
+  LDFLAGS+=-nostdlib
+endif
+
 ifeq ($(USE_GCC),1)
   ## Toolchain setup
   CC=$(CROSS_COMPILE)gcc

include/wolfboot/wolfboot.h

@@ -46,7 +46,17 @@ extern "C" {
 #ifndef RAMFUNCTION
 #  if defined(__WOLFBOOT) && defined(RAM_CODE)
 #    if defined(ARCH_ARM)
-#      define RAMFUNCTION __attribute__((used,section(".ramcode"),long_call))
+#      if defined(__has_attribute)
+#        if __has_attribute(long_call)
+#          define RAMFUNCTION __attribute__((used,section(".ramcode"),long_call))
+#        else
+#          define RAMFUNCTION __attribute__((used,section(".ramcode")))
+#        endif
+#      elif defined(__GNUC__)
+#        define RAMFUNCTION __attribute__((used,section(".ramcode"),long_call))
+#      else
+#        define RAMFUNCTION __attribute__((used,section(".ramcode")))
+#      endif
 #    elif defined(ARCH_PPC)
 #      define RAMFUNCTION __attribute__((used,section(".ramcode"),longcall))
 #    else

options.mk

@@ -1,8 +1,19 @@
 WOLFCRYPT_OBJS+=$(WOLFBOOT_LIB_WOLFSSL)/wolfcrypt/src/asn.o
-USE_GCC?=1
+USE_CLANG?=0
+ifeq ($(USE_CLANG),1)
+  USE_GCC?=0
+else
+  USE_GCC?=1
+endif
 WOLFBOOT_TEST_FILLER?=0
 WOLFBOOT_TIME_TEST?=0
 
+ifeq ($(USE_CLANG),1)
+  ifeq ($(USE_GCC),1)
+    $(error USE_CLANG=1 is incompatible with USE_GCC=1; set USE_GCC=0)
+  endif
+endif
+
 # Support for Built-in ROT into OTP flash memory
 ifeq ($(FLASH_OTP_KEYSTORE),1)
     CFLAGS+=-D"FLASH_OTP_KEYSTORE"
@@ -722,7 +733,9 @@ ifeq ($(DEBUG_SYMBOLS),1)
   ifeq ($(USE_GCC),1)
     CFLAGS+=-ggdb3
   else ifneq ($(ARCH),AURIX_TC3)
+    ifneq ($(USE_CLANG),1)
     CFLAGS+=-gstabs
+    endif
   endif
 endif
 
@@ -1030,9 +1043,13 @@ CFLAGS+=$(CFLAGS_EXTRA)
 OBJS+=$(OBJS_EXTRA)
 
 ifeq ($(USE_GCC_HEADLESS),1)
-  ifneq ($(ARCH),RENESAS_RX)
-    ifneq ($(ARCH),AURIX_TC3)
-      CFLAGS+="-Wstack-usage=$(STACK_USAGE)"
+  ifeq ($(USE_GCC),1)
+    ifneq ($(USE_CLANG),1)
+      ifneq ($(ARCH),RENESAS_RX)
+        ifneq ($(ARCH),AURIX_TC3)
+          CFLAGS+="-Wstack-usage=$(STACK_USAGE)"
+        endif
+      endif
     endif
   endif
 endif

src/update_flash.c

@@ -754,9 +754,11 @@ static int wolfBoot_delta_update(struct wolfBoot_image *boot,
 
 
 #ifdef WOLFBOOT_ARMORED
-#    ifdef __GNUC__
+#    if defined(__GNUC__) && !defined(__clang__)
 #        pragma GCC push_options
 #        pragma GCC optimize("O0")
+#    elif defined(__clang__)
+#        pragma clang optimize off
 #    elif defined(__IAR_SYSTEMS_ICC__)
 #        pragma optimize=none
 #    endif
@@ -1474,8 +1476,10 @@ void RAMFUNCTION wolfBoot_start(void)
 }
 
 #ifdef WOLFBOOT_ARMORED
-#    ifdef __GNUC__
+#    if defined(__GNUC__) && !defined(__clang__)
 #        pragma GCC pop_options
+#    elif defined(__clang__)
+#        pragma clang optimize on
 #    elif defined(__IAR_SYSTEMS_ICC__)
 #        pragma optimize=default
 #    endif

test-app/Makefile

@@ -22,7 +22,12 @@ endif
 CFLAGS+=-I. -I..
 DEBUG?=1
 DELTA_DATA_SIZE?=2000
-USE_GCC?=1
+USE_CLANG?=0
+ifeq ($(USE_CLANG),1)
+  USE_GCC?=0
+else
+  USE_GCC?=1
+endif
 USE_GCC_HEADLESS?=1
 BOOTLOADER_PARTITION_SIZE?=$$(( $(WOLFBOOT_PARTITION_BOOT_ADDRESS) - $(ARCH_FLASH_OFFSET)))
 
@@ -57,14 +62,18 @@ else
   CFLAGS+=-Wall -ffreestanding -Wno-unused
   # Stack usage computation not supported on TriCore
   ifneq ($(ARCH),AURIX_TC3)
-    CFLAGS+=-Wstack-usage=1024 -nostartfiles
+    ifneq ($(USE_CLANG),1)
+      CFLAGS+=-Wstack-usage=1024
+    endif
   endif
   CFLAGS+=-DTARGET_$(TARGET) -I../include
   CFLAGS+=-g
   ifeq ($(USE_GCC),1)
     CFLAGS+=-ggdb3
   else ifneq ($(ARCH),AURIX_TC3)
-    CFLAGS+=-gstabs
+    ifneq ($(USE_CLANG),1)
+      CFLAGS+=-gstabs
+    endif
   endif
 
   ifeq ($(ARCH),RENESAS_RX)
@@ -78,14 +87,18 @@ endif
 
 include ../arch.mk
 
+ifeq ($(USE_CLANG),1)
+  APP_OBJS+=../src/string.o
+endif
+
 # Optional alias for clearer TZ PSA selection in app builds.
 ifeq ($(WOLFCRYPT_TZ_PSA),1)
   WOLFCRYPT_TZ=1
   WOLFCRYPT_TZ_PSA=1
 endif
 
 # Setup default linker flags
-LDFLAGS+=-T $(LSCRIPT) -Wl,-gc-sections -Wl,-Map=image.map
+LDFLAGS+=-T $(LSCRIPT) -Wl,-gc-sections -Wl,-Map=image.map -nostartfiles
 
 # Setup default objcopy flags
 OBJCOPY_FLAGS+=--gap-fill $(FILL_BYTE)