syscall: use per-CPU WCET slots and ulmk_wcet_bind

- Global slot collided under SMP; bind a private sample per thread
- Enables secondary cycle counters used by silicon_wcet on TC275

Author: uLipe

include/ulmk/syscall_wcet.h

@@ -2,17 +2,20 @@
 /*
  * Syscall WCET slot — filled by the kernel when ULMK_CONFIG_SYSCALL_WCET=1.
  *
- * Lives in .user_bss so driver threads may read it without mem_map.
- * After each syscall the kernel updates nr/delta/begin/end/blocked and
- * increments seq.
+ * g_ulmk_syscall_wcet[cpu] is the last sample on that CPU (debug / legacy).
+ * For correct measurement when more than one thread runs on a CPU (IPC),
+ * bind a private slot with ulmk_wcet_bind() — the kernel then also writes
+ * that thread's samples there, without peer overwrite.
  */
 
 #ifndef ULMK_SYSCALL_WCET_H
 #define ULMK_SYSCALL_WCET_H
 
 #include <stdint.h>
 
-#define ULMK_SYSCALL_WCET_MAGIC	0x57434554u	/* 'WCET' */
+#define ULMK_SYSCALL_WCET_MAGIC		0x57434554u	/* 'WCET' */
+
+#define ULMK_SYSCALL_WCET_MAX_CPUS	8u
 
 struct ulmk_syscall_wcet_slot {
 	uint32_t magic;
@@ -30,6 +33,7 @@ struct ulmk_syscall_wcet_slot {
 	uint32_t blocked;
 };
 
-extern volatile struct ulmk_syscall_wcet_slot g_ulmk_syscall_wcet;
+extern volatile struct ulmk_syscall_wcet_slot
+	g_ulmk_syscall_wcet[ULMK_SYSCALL_WCET_MAX_CPUS];
 
 #endif /* ULMK_SYSCALL_WCET_H */

kernel/include/ulmk_syscall_wcet_internal.h

@@ -11,6 +11,8 @@
 
 struct ulmk_thread;
 
+uint32_t ulmk_kern_wcet_bind(uint32_t slot_ptr);
+
 #if ULMK_CONFIG_SYSCALL_WCET
 void ulmk_syscall_wcet_account_reset(void);
 uint32_t ulmk_syscall_wcet_blocked_cycles(void);

kernel/syscall/syscall_wcet.c

@@ -7,12 +7,14 @@
  */
 
 #include <ulmk/syscall_wcet.h>
+#include <ulmk/microkernel.h>
 #include <ulmk/config.h>
 #include <ulmk_arch.h>
 #include <kernel/include/ulmk_sched.h>
 #include <kernel/include/ulmk_thread_internal.h>
 
-volatile struct ulmk_syscall_wcet_slot g_ulmk_syscall_wcet
+volatile struct ulmk_syscall_wcet_slot
+g_ulmk_syscall_wcet[ULMK_SYSCALL_WCET_MAX_CPUS]
 	__attribute__((section(".user_bss")));
 
 #if ULMK_CONFIG_SYSCALL_WCET
@@ -56,4 +58,29 @@ void ulmk_syscall_wcet_block_end_th(struct ulmk_thread *th)
 	t->wcet_block_open = 0u;
 }
 
+uint32_t ulmk_kern_wcet_bind(uint32_t slot_ptr)
+{
+	ulmk_thread_t *cur = ulmk_sched_current();
+	volatile struct ulmk_syscall_wcet_slot *slot;
+
+	if (!cur)
+		return (uint32_t)(int32_t)ULMK_EINVAL;
+
+	slot = (volatile struct ulmk_syscall_wcet_slot *)(uintptr_t)slot_ptr;
+	cur->wcet_out = slot;
+	if (slot) {
+		slot->magic = ULMK_SYSCALL_WCET_MAGIC;
+		slot->seq   = 0u;
+	}
+	return (uint32_t)ULMK_OK;
+}
+
+#else /* !ULMK_CONFIG_SYSCALL_WCET */
+
+uint32_t ulmk_kern_wcet_bind(uint32_t slot_ptr)
+{
+	(void)slot_ptr;
+	return (uint32_t)(int32_t)ULMK_EINVAL;
+}
+
 #endif /* ULMK_CONFIG_SYSCALL_WCET */