arch/arm: introduce the pre-stack/RAM init hook

arch/arm/core/cortex_m/reset.S

@@ -35,6 +35,10 @@ GTEXT(z_arm_init_arch_hw_at_boot)
 #if defined(CONFIG_PM_S2RAM)
 GTEXT(arch_pm_s2ram_resume)
 #endif
+#if defined(CONFIG_SOC_EARLY_RESET_HOOK)
+GTEXT(soc_early_reset_hook)
+#endif
+
 
 /*
  * PACBTI Mask for CONTROL register:
@@ -100,6 +104,10 @@ SECTION_SUBSEC_FUNC(TEXT,_reset_section,__start)
 
 #endif /* CONFIG_INIT_ARCH_HW_AT_BOOT */
 
+#if defined(CONFIG_SOC_EARLY_RESET_HOOK)
+    /* Call custom code that executes before any stack is set up or RAM memory is accessed */
+    bl soc_early_reset_hook
+#endif
 #if defined(CONFIG_PM_S2RAM)
     /*
      * Temporarily set MSP to interrupt stack so that arch_pm_s2ram_resume can

include/zephyr/platform/hooks.h

@@ -19,6 +19,19 @@
  * directly from application code but may be freely used within the OS.
  */
 
+#ifdef CONFIG_SOC_EARLY_RESET_HOOK
+/**
+ * @brief SoC hook executed before data RAM initialization, at the beginning
+ * of the reset vector.
+ *
+ * This hook is implemented by the SoC and can be used to perform any
+ * SoC-specific initialization. Refer to :kconfig:option:`SOC_EARLY_RESET_HOOK`
+ * and relevant architecture zephyr-rtos startup implementation for more details.
+ */
+void soc_early_reset_hook(void);
+#else
+#define soc_early_reset_hook() do { } while (0)
+#endif
 
 #ifdef CONFIG_SOC_RESET_HOOK
 /**

kernel/Kconfig.init

@@ -6,13 +6,40 @@
 
 menu "SoC and Board Hooks"
 
-config SOC_RESET_HOOK
-	bool "Run early SoC reset hook"
+config SOC_EARLY_RESET_HOOK
+	bool "Run SoC-specific early reset hook"
 	help
-	  Run an early SoC reset hook.
+	  Run a SoC-specific hook early in the reset/startup code (__start).
+	  A custom hook soc_early_reset_hook() will be executed at the beginning
+	  of the architecture-specific startup code, after hardware has been
+	  configured (as required by CONFIG_INIT_ARCH_HW_AT_BOOT) but before
+	  architecture's own resume logic.
+
+	  Returning from this hook is not mandatory: it can be used to implement
+	  special logic to resume execution in some scenarios (for example, when
+	  a bootloader is used).
+
+	  The stack pointer register should be considered as not initialized upon
+	  call to this hook. In particular, this means that the hook is NOT allowed
+	  to "push" any data using this stack pointer value. However, the hook may
+	  use an implementation-specific area as stack if desired; in such case,
+	  the original value of the stack pointer needs not to be "restored" before
+	  returning control to the hook's caller.
 
-	  A custom hook soc_reset_hook() is executed at the beginning of the
-	  startup code (__start). soc_reset_hook() must be implemented by the SoC.
+	  Additional constraints may be imposed on the hook by the architecture.
+
+config SOC_RESET_HOOK
+	bool "Run SoC-specific reset hook"
+	help
+	  Run a SoC-specific hook in the reset/startup code (__start).
+
+	  A custom hook soc_reset_hook() will be executed near the beginning
+	  of the architecture-specific startup code, after hardware has been
+	  configured (as required by CONFIG_INIT_ARCH_HW_AT_BOOT), a stack
+	  pointer has been loaded and the architecture's own resume logic
+	  has executed (if CONFIG_PM_S2RAM is enabled). Because this hook
+	  runs after the resume logic, it is not called when the system
+	  resumes from a suspend-to-RAM power state.
 
 config SOC_PREP_HOOK
 	bool "Run early SoC preparation hook"