riscv: pmp: move the null pointer trap first

Let's move the null pointer trap first so to give set_pmp_entry() the
opportunity to use a single-slot TOR entry.

Signed-off-by: Nicolas Pitre <[email protected]>

Author: Nicolas Pitre

arch/riscv/core/pmp.c

@@ -422,12 +422,6 @@ void z_riscv_pmp_init(void)
 	unsigned long pmp_cfg[CONFIG_PMP_SLOTS / PMPCFG_STRIDE];
 	unsigned int index = 0;
 
-	/* The read-only area is always there for every mode */
-	set_pmp_entry(&index, PMP_R | PMP_X | PMP_L,
-		      (uintptr_t)__rom_region_start,
-		      (size_t)__rom_region_size,
-		      pmp_addr, pmp_cfg, ARRAY_SIZE(pmp_addr));
-
 #ifdef CONFIG_NULL_POINTER_EXCEPTION_DETECTION_PMP
 	/*
 	 * Use a PMP slot to make region (starting at address 0x0) inaccessible
@@ -439,6 +433,12 @@ void z_riscv_pmp_init(void)
 		      pmp_addr, pmp_cfg, ARRAY_SIZE(pmp_addr));
 #endif
 
+	/* The read-only area is always there for every mode */
+	set_pmp_entry(&index, PMP_R | PMP_X | PMP_L,
+		      (uintptr_t)__rom_region_start,
+		      (size_t)__rom_region_size,
+		      pmp_addr, pmp_cfg, ARRAY_SIZE(pmp_addr));
+
 #ifdef CONFIG_PMP_STACK_GUARD
 #ifdef CONFIG_MULTITHREADING
 	/*