soc: nxp: s32k3: gate IVT emission when chain-loaded by MCUboot

Emit the IVT section and IVT header only when XIP and the image is either
a standalone XIP app or MCUboot itself. Do not emit the IVT when the
Zephyr image is chain-loaded by MCUboot (BOOTLOADER_MCUBOOT=y).

- linker.ld/sections.ld: place .ivt_header at IVT_HEADER only under
XIP && (!BOOTLOADER_MCUBOOT || MCUBOOT).
Provide __ivt_region_start/end symbols.
- soc.c: guard IVT struct under the same condition and mark it 'used'
so the linker keeps it when needed.
- Kconfig.defconfig - Make the bootloader and the sign tool compatible
with the vector table.

This avoids populating 0x400000 IVT from the app image while retaining it
for MCUboot or standalone XIP use-cases.

Signed-off-by: Sumit Batra <sumit.batra@nxp.com>

Author: sumitbatra-nxp

soc/nxp/s32/s32k3/Kconfig.defconfig

@@ -28,4 +28,9 @@ endif # ETH_DRIVER && NET_L2_ETHERNET
 config CACHE_MANAGEMENT
 	default y
 
+# S32K3 places the vector table at +0x400
+# This makes the bootloader and the sign tool compatible with that.
+config ROM_START_OFFSET
+	default 0x400 if BOOTLOADER_MCUBOOT
+
 endif # SOC_SERIES_S32K3

soc/nxp/s32/s32k3/linker.ld

@@ -4,12 +4,20 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-#ifdef CONFIG_XIP
+/* Emit IVT section only when XIP and (standalone app OR MCUboot itself) */
+#if defined(CONFIG_XIP) && (!defined(CONFIG_BOOTLOADER_MCUBOOT) || defined(CONFIG_MCUBOOT))
+
 MEMORY
 {
-	IVT_HEADER (r) : ORIGIN = CONFIG_FLASH_BASE_ADDRESS + CONFIG_IVT_HEADER_OFFSET,
+	IVT_HEADER (r) : ORIGIN = (CONFIG_FLASH_BASE_ADDRESS + CONFIG_IVT_HEADER_OFFSET),
 			 LENGTH = CONFIG_IVT_HEADER_SIZE
 }
+
+/* Symbols for IVT */
+PROVIDE(__ivt_region_start = ORIGIN(IVT_HEADER));
+PROVIDE(__ivt_region_end   = ORIGIN(IVT_HEADER) + LENGTH(IVT_HEADER));
+
 #endif
 
+/* Include standard Zephyr ARM script */
 #include <zephyr/arch/arm/cortex_m/scripts/linker.ld>

soc/nxp/s32/s32k3/sections.ld

@@ -4,10 +4,14 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-#ifdef CONFIG_XIP
+/* Emit IVT section only when XIP and (standalone app OR MCUboot itself) */
+#if defined(CONFIG_XIP) && (!defined(CONFIG_BOOTLOADER_MCUBOOT) || defined(CONFIG_MCUBOOT))
 
-.ivt_header : {
-	KEEP(*(.ivt_header));
+/* IVT at flash base */
+.ivt_header ORIGIN(IVT_HEADER) : ALIGN(4)
+{
+	/* Using a wildcard makes it more robust */
+	KEEP(*(.ivt_header*));
 } > IVT_HEADER
 
 #else

soc/nxp/s32/s32k3/soc.c

@@ -13,6 +13,11 @@
 #include <OsIf.h>
 
 #ifdef CONFIG_XIP
+/*
+ * Emit IVT only for standalone XIP or MCUboot itself
+ * But not for the cases where Zephyr Image is loaded by MCUboot
+ */
+#if !defined(CONFIG_BOOTLOADER_MCUBOOT) || defined(CONFIG_MCUBOOT)
 /* Image Vector Table structure definition for S32K3XX */
 struct ivt {
 	uint32_t header;
@@ -33,20 +38,23 @@ struct ivt {
 extern char _vector_start[];
 
 /*
+ * Attribute 'used' forces the compiler to emit ivt_header
+ * even if nothing references it.
  * IVT for SoC S32K344, the minimal boot configuration is:
  * - Watchdog (SWT0) is disabled (default value).
  * - Non-Secure Boot is used (default value).
  * - Ungate clock for Cortex-M7_0 after boot.
  * - Application start address of Cortex-M7_0 is application's vector table.
  */
-const struct ivt ivt_header __attribute__((section(".ivt_header"))) = {
+const struct ivt ivt_header __attribute__((section(".ivt_header"), used)) = {
 	.header = IVT_MAGIC_MARKER,
 	.boot_configure = 1,
 	.cm7_0_start_address = (const void *)_vector_start,
 	.cm7_1_start_address = NULL,
 	.cm7_2_start_address = NULL,
 	.lc_configure = NULL,
 };
+#endif
 #endif /* CONFIG_XIP */
 
 void soc_early_init_hook(void)