Make sure FPSCR is properly initialized

This is a potentially breaking change as the register was left with an unpredictable/unspecified value. Config: default NaN mode enabled, flush-to-zero enabled, and round to nearest.
devkitPro · Apr 12, 2022 · 1168687 · 1168687
1 parent c36d9cc
commit 1168687
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Showing 3 changed files with 30 additions and 24 deletions.
diff --git a/libctru/source/internal.h b/libctru/source/internal.h
@@ -31,7 +31,20 @@ typedef struct
 	bool srv_blocking_policy;
 } ThreadVars;
 
+struct Thread_tag
+{
+	Handle handle;
+	ThreadFunc ep;
+	void* arg;
+	int rc;
+	bool detached, finished;
+	struct _reent reent;
+	void* stacktop;
+};
+
 static inline ThreadVars* getThreadVars(void)
 {
 	return (ThreadVars*)getThreadLocalStorage();
 }
+
+void initThreadVars(struct Thread_tag *thread);
diff --git a/libctru/source/system/syscalls.c b/libctru/source/system/syscalls.c
@@ -99,18 +99,27 @@ void __SYSCALL(exit)(int rc) {
 	__ctru_exit(rc);
 }
 
-
-void __system_initSyscalls(void)
+void initThreadVars(struct Thread_tag *thread)
 {
-
-	// Initialize thread vars for the main thread
 	ThreadVars* tv = getThreadVars();
 	tv->magic = THREADVARS_MAGIC;
-	tv->reent = _impure_ptr;
-	tv->thread_ptr = NULL;
-	tv->tls_tp = __tls_start-8; // ARM ELF TLS ABI mandates an 8-byte header
+	tv->reent = thread != NULL ? &thread->reent : _impure_ptr;
+	tv->thread_ptr = thread;
+	tv->tls_tp = (thread != NULL ? (u8*)thread->stacktop : __tls_start) - 8; // Arm ELF TLS ABI mandates an 8-byte header
 	tv->srv_blocking_policy = false;
 
+	// Kernel does not initialize fpscr at all, so we must do it ourselves
+	// https://developer.arm.com/documentation/ddi0360/f/vfp-programmers-model/vfp11-system-registers/floating-point-status-and-control-register--fpscr
+
+	// All flags clear, all interrupts disabled, all instruction scalar.
+	// As for the 3 below fields: default NaN mode, flush-to-zero both enabled & round to nearest.
+	__builtin_arm_set_fpscr(BIT(25) | BIT(24) | (0u << 22));
+}
+
+void __system_initSyscalls(void)
+{
+	// Initialize thread vars for the main thread
+	initThreadVars(NULL);
 	u32 tls_size = __tdata_lma_end - __tdata_lma;
 	if (tls_size)
 		memcpy(__tls_start, __tdata_lma, tls_size);

diff --git a/libctru/source/thread.c b/libctru/source/thread.c
@@ -8,17 +8,6 @@ extern const u8 __tdata_lma_end[];
 extern u8 __tls_start[];
 extern u8 __tls_end[];
 
-struct Thread_tag
-{
-	Handle handle;
-	ThreadFunc ep;
-	void* arg;
-	int rc;
-	bool detached, finished;
-	struct _reent reent;
-	void* stacktop;
-};
-
 static void __panic(void)
 {
 	svcBreak(USERBREAK_PANIC);
@@ -28,12 +17,7 @@ static void __panic(void)
 static void _thread_begin(void* arg)
 {
 	Thread t = (Thread)arg;
-	ThreadVars* tv = getThreadVars();
-	tv->magic = THREADVARS_MAGIC;
-	tv->reent = &t->reent;
-	tv->thread_ptr = t;
-	tv->tls_tp = (u8*)t->stacktop-8; // ARM ELF TLS ABI mandates an 8-byte header
-	tv->srv_blocking_policy = false;
+	initThreadVars(t);
 	t->ep(t->arg);
 	threadExit(0);
 }