kcov: add prototypes for helper functions

A number of internal functions in kcov are only called from generated code
and don't technically need a declaration, but 'make W=1' warns about
global symbols without a prototype:

kernel/kcov.c:199:14: error: no previous prototype for '__sanitizer_cov_trace_pc' [-Werror=missing-prototypes]
kernel/kcov.c:264:14: error: no previous prototype for '__sanitizer_cov_trace_cmp1' [-Werror=missing-prototypes]
kernel/kcov.c:270:14: error: no previous prototype for '__sanitizer_cov_trace_cmp2' [-Werror=missing-prototypes]
kernel/kcov.c:276:14: error: no previous prototype for '__sanitizer_cov_trace_cmp4' [-Werror=missing-prototypes]
kernel/kcov.c:282:14: error: no previous prototype for '__sanitizer_cov_trace_cmp8' [-Werror=missing-prototypes]
kernel/kcov.c:288:14: error: no previous prototype for '__sanitizer_cov_trace_const_cmp1' [-Werror=missing-prototypes]
kernel/kcov.c:295:14: error: no previous prototype for '__sanitizer_cov_trace_const_cmp2' [-Werror=missing-prototypes]
kernel/kcov.c:302:14: error: no previous prototype for '__sanitizer_cov_trace_const_cmp4' [-Werror=missing-prototypes]
kernel/kcov.c:309:14: error: no previous prototype for '__sanitizer_cov_trace_const_cmp8' [-Werror=missing-prototypes]
kernel/kcov.c:316:14: error: no previous prototype for '__sanitizer_cov_trace_switch' [-Werror=missing-prototypes]

Adding prototypes for these in a header solves that problem, but now there
is a mismatch between the built-in type and the prototype on 64-bit
architectures because they expect some functions to take a 64-bit
'unsigned long' argument rather than an 'unsigned long long' u64 type:

include/linux/kcov.h:84:6: error: conflicting types for built-in function '__sanitizer_cov_trace_switch'; expected 'void(long long unsigned int,  void *)' [-Werror=builtin-declaration-mismatch]
   84 | void __sanitizer_cov_trace_switch(u64 val, u64 *cases);
      |      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~

Avoid this as well with a custom type definition.

Link: https://lkml.kernel.org/r/20230517124944.929997-1-arnd@kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Rong Tao <rongtao@cestc.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/kcov.h

@@ -72,6 +72,23 @@ static inline void kcov_remote_stop_softirq(void)
 		kcov_remote_stop();
 }
 
+#ifdef CONFIG_64BIT
+typedef unsigned long kcov_u64;
+#else
+typedef unsigned long long kcov_u64;
+#endif
+
+void __sanitizer_cov_trace_pc(void);
+void __sanitizer_cov_trace_cmp1(u8 arg1, u8 arg2);
+void __sanitizer_cov_trace_cmp2(u16 arg1, u16 arg2);
+void __sanitizer_cov_trace_cmp4(u32 arg1, u32 arg2);
+void __sanitizer_cov_trace_cmp8(kcov_u64 arg1, kcov_u64 arg2);
+void __sanitizer_cov_trace_const_cmp1(u8 arg1, u8 arg2);
+void __sanitizer_cov_trace_const_cmp2(u16 arg1, u16 arg2);
+void __sanitizer_cov_trace_const_cmp4(u32 arg1, u32 arg2);
+void __sanitizer_cov_trace_const_cmp8(kcov_u64 arg1, kcov_u64 arg2);
+void __sanitizer_cov_trace_switch(kcov_u64 val, void *cases);
+
 #else
 
 static inline void kcov_task_init(struct task_struct *t) {}

kernel/kcov.c

@@ -279,7 +279,7 @@ void notrace __sanitizer_cov_trace_cmp4(u32 arg1, u32 arg2)
 }
 EXPORT_SYMBOL(__sanitizer_cov_trace_cmp4);
 
-void notrace __sanitizer_cov_trace_cmp8(u64 arg1, u64 arg2)
+void notrace __sanitizer_cov_trace_cmp8(kcov_u64 arg1, kcov_u64 arg2)
 {
 	write_comp_data(KCOV_CMP_SIZE(3), arg1, arg2, _RET_IP_);
 }
@@ -306,16 +306,17 @@ void notrace __sanitizer_cov_trace_const_cmp4(u32 arg1, u32 arg2)
 }
 EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp4);
 
-void notrace __sanitizer_cov_trace_const_cmp8(u64 arg1, u64 arg2)
+void notrace __sanitizer_cov_trace_const_cmp8(kcov_u64 arg1, kcov_u64 arg2)
 {
 	write_comp_data(KCOV_CMP_SIZE(3) | KCOV_CMP_CONST, arg1, arg2,
 			_RET_IP_);
 }
 EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp8);
 
-void notrace __sanitizer_cov_trace_switch(u64 val, u64 *cases)
+void notrace __sanitizer_cov_trace_switch(kcov_u64 val, void *arg)
 {
 	u64 i;
+	u64 *cases = arg;
 	u64 count = cases[0];
 	u64 size = cases[1];
 	u64 type = KCOV_CMP_CONST;