arch: arm: cortex_m: generalizing SRAM vector table relocation

Allow to place the vector table section in SRAM with
CONFIG_SRAM_VECTOR_TABLE option for all cortex-m architecture that
have VTOR register.

Signed-off-by: Martin Hoff <[email protected]>

Author: Martinhoff-maker

arch/arm/core/cortex_m/CMakeLists.txt

@@ -61,3 +61,13 @@ zephyr_linker_sources(
   vt_pointer_section.ld
   )
 endif()
+
+if (CONFIG_CPU_CORTEX_M_HAS_VTOR)
+zephyr_linker_sources_ifdef(CONFIG_SRAM_VECTOR_TABLE
+  RAM_SECTIONS
+  # Maybe need to be changed in order to be placed at the beginning of RAM
+  # (conflict with code relocation script)
+  SORT_KEY 0
+  ram_vector_table.ld
+)
+endif()

arch/arm/core/cortex_m/prep_c.c

@@ -39,7 +39,11 @@ Z_GENERIC_SECTION(.vt_pointer_section) __attribute__((used)) void *_vector_table
 
 #ifdef CONFIG_CPU_CORTEX_M_HAS_VTOR
 
+#ifdef CONFIG_SRAM_VECTOR_TABLE
+#define VECTOR_ADDRESS ((uintptr_t)_sram_vector_start)
+#else
 #define VECTOR_ADDRESS ((uintptr_t)_vector_start)
+#endif
 
 /* In some Cortex-M3 implementations SCB_VTOR bit[29] is called the TBLBASE bit */
 #ifdef SCB_VTOR_TBLBASE_Msk
@@ -50,6 +54,12 @@ Z_GENERIC_SECTION(.vt_pointer_section) __attribute__((used)) void *_vector_table
 
 void __weak relocate_vector_table(void)
 {
+#ifdef CONFIG_SRAM_VECTOR_TABLE
+	/* Copy vector table to its location in SRAM */
+	size_t vector_size = (size_t)_vector_end - (size_t)_vector_start;
+
+	z_early_memcpy(_sram_vector_start, _vector_start, vector_size);
+#endif
 	SCB->VTOR = VECTOR_ADDRESS & VTOR_MASK;
 	barrier_dsync_fence_full();
 	barrier_isync_fence_full();

arch/arm/core/cortex_m/ram_vector_table.ld

@@ -0,0 +1,32 @@
+/*
+ * Copyright (c) 2025 Silicon Laboratories Inc.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/* Vector table is not necessarily at the start of the RAM region: in the case where Zephyr code
+ * relocation is used, the vector table is placed after the relocated code.
+ * Relocated code is always placed at the start of the RAM SECTION because of the hard-coded value
+ * generated by "gen_relocate_app.py" in the file. It can create quite a big gap and lose about the
+ * size of alignment in RAM space.
+ */
+
+SECTION_PROLOGUE(.sram_vt,,)
+{
+	/* Heritage of vector table alignment in flash (see vector_table.ld in arch/arm/core/) */
+#if defined(CONFIG_ARMV6_M_ARMV8_M_BASELINE)
+	. = ALIGN( 1 << LOG2CEIL(4 * 64) );
+#elif defined(CONFIG_ARMV7_M_ARMV8_M_MAINLINE)
+	. = ALIGN( 1 << LOG2CEIL(4 * 32) );
+#else
+#error "Unsupported architecture variant"
+#endif
+
+	. = ALIGN( 1 << LOG2CEIL(4 * (16 + CONFIG_NUM_IRQS)) );
+
+	_sram_vector_start = .;
+	. += _vector_end - _vector_start;
+	MPU_ALIGN(_sram_vector_size);
+	_sram_vector_end = .;
+} GROUP_DATA_LINK_IN(RAMABLE_REGION, ROMABLE_REGION)
+_sram_vector_size = _sram_vector_end - _sram_vector_start;

arch/arm/core/mpu/arm_core_mpu.c

@@ -63,6 +63,11 @@ extern char __ram_text_reloc_start[];
 extern char __ram_text_reloc_size[];
 #endif
 
+#if defined(CONFIG_SRAM_VECTOR_TABLE)
+extern char _sram_vector_start[];
+extern char _sram_vector_size[];
+#endif
+
 static const struct z_arm_mpu_partition static_regions[] = {
 #if defined(CONFIG_COVERAGE_GCOV) && defined(CONFIG_USERSPACE)
 	{
@@ -106,6 +111,18 @@ static const struct z_arm_mpu_partition static_regions[] = {
 #endif
 	},
 #endif /* CONFIG_CODE_DATA_RELOCATION_SRAM */
+#if defined(CONFIG_SRAM_VECTOR_TABLE)
+	{
+		/* Vector table in SRAM */
+		.start = (uint32_t)&_sram_vector_start,
+		.size = (uint32_t)&_sram_vector_size,
+#if defined(CONFIG_ARM_MPU_PXN) && defined(CONFIG_USERSPACE)
+		.attr = K_MEM_PARTITION_P_R_U_RX,
+#else
+		.attr = K_MEM_PARTITION_P_RO_U_RO,
+#endif
+	},
+#endif /* CONFIG_SRAM_VECTOR_TABLE */
 #if !defined(CONFIG_MULTITHREADING) && defined(CONFIG_MPU_STACK_GUARD)
 	/* Main stack MPU guard to detect overflow.
 	 * Note:

include/zephyr/linker/linker-defs.h

@@ -154,6 +154,12 @@ extern char _vector_end[];
 extern char __vector_relay_table[];
 #endif
 
+#ifdef CONFIG_SRAM_VECTOR_TABLE
+extern char _sram_vector_start[];
+extern char _sram_vector_end[];
+extern char _sram_vector_size[];
+#endif
+
 #ifdef CONFIG_COVERAGE_GCOV
 extern char __gcov_bss_start[];
 extern char __gcov_bss_end[];