riscv: for C functions called only from assembly, mark with __visible

Rather than adding prototypes for C functions called only by assembly
code, mark them as __visible.  This avoids adding prototypes that will
never be used by the callers.  Resolves the following sparse warnings:

arch/riscv/kernel/irq.c:27:29: warning: symbol 'do_IRQ' was not declared. Should it be static?
arch/riscv/kernel/ptrace.c:151:6: warning: symbol 'do_syscall_trace_enter' was not declared. Should it be static?
arch/riscv/kernel/ptrace.c:165:6: warning: symbol 'do_syscall_trace_exit' was not declared. Should it be static?
arch/riscv/kernel/signal.c:295:17: warning: symbol 'do_notify_resume' was not declared. Should it be static?
arch/riscv/kernel/traps.c:92:1: warning: symbol 'do_trap_unknown' was not declared. Should it be static?
arch/riscv/kernel/traps.c:94:1: warning: symbol 'do_trap_insn_misaligned' was not declared. Should it be static?
arch/riscv/kernel/traps.c:96:1: warning: symbol 'do_trap_insn_fault' was not declared. Should it be static?
arch/riscv/kernel/traps.c:98:1: warning: symbol 'do_trap_insn_illegal' was not declared. Should it be static?
arch/riscv/kernel/traps.c:100:1: warning: symbol 'do_trap_load_misaligned' was not declared. Should it be static?
arch/riscv/kernel/traps.c:102:1: warning: symbol 'do_trap_load_fault' was not declared. Should it be static?
arch/riscv/kernel/traps.c:104:1: warning: symbol 'do_trap_store_misaligned' was not declared. Should it be static?
arch/riscv/kernel/traps.c:106:1: warning: symbol 'do_trap_store_fault' was not declared. Should it be static?
arch/riscv/kernel/traps.c:108:1: warning: symbol 'do_trap_ecall_u' was not declared. Should it be static?
arch/riscv/kernel/traps.c:110:1: warning: symbol 'do_trap_ecall_s' was not declared. Should it be static?
arch/riscv/kernel/traps.c:112:1: warning: symbol 'do_trap_ecall_m' was not declared. Should it be static?
arch/riscv/kernel/traps.c:124:17: warning: symbol 'do_trap_break' was not declared. Should it be static?
arch/riscv/kernel/smpboot.c:136:24: warning: symbol 'smp_callin' was not declared. Should it be static?

Based on a suggestion from Luc Van Oostenryck.

This version includes changes based on feedback from Christoph Hellwig
<hch@lst.de>.
Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de> # for do_syscall_trace_*

arch/riscv/kernel/irq.c

@@ -24,7 +24,7 @@ int arch_show_interrupts(struct seq_file *p, int prec)
 	return 0;
 }
 
-asmlinkage void __irq_entry do_IRQ(struct pt_regs *regs)
+asmlinkage __visible void __irq_entry do_IRQ(struct pt_regs *regs)
 {
 	struct pt_regs *old_regs = set_irq_regs(regs);
 

arch/riscv/kernel/ptrace.c

@@ -148,7 +148,7 @@ long arch_ptrace(struct task_struct *child, long request,
  * Allows PTRACE_SYSCALL to work.  These are called from entry.S in
  * {handle,ret_from}_syscall.
  */
-void do_syscall_trace_enter(struct pt_regs *regs)
+__visible void do_syscall_trace_enter(struct pt_regs *regs)
 {
 	if (test_thread_flag(TIF_SYSCALL_TRACE))
 		if (tracehook_report_syscall_entry(regs))
@@ -162,7 +162,7 @@ void do_syscall_trace_enter(struct pt_regs *regs)
 	audit_syscall_entry(regs->a7, regs->a0, regs->a1, regs->a2, regs->a3);
 }
 
-void do_syscall_trace_exit(struct pt_regs *regs)
+__visible void do_syscall_trace_exit(struct pt_regs *regs)
 {
 	audit_syscall_exit(regs);
 

arch/riscv/kernel/signal.c

@@ -292,8 +292,8 @@ static void do_signal(struct pt_regs *regs)
  * notification of userspace execution resumption
  * - triggered by the _TIF_WORK_MASK flags
  */
-asmlinkage void do_notify_resume(struct pt_regs *regs,
-	unsigned long thread_info_flags)
+asmlinkage __visible void do_notify_resume(struct pt_regs *regs,
+					   unsigned long thread_info_flags)
 {
 	/* Handle pending signal delivery */
 	if (thread_info_flags & _TIF_SIGPENDING)

arch/riscv/kernel/smpboot.c

@@ -133,7 +133,7 @@ void __init smp_cpus_done(unsigned int max_cpus)
 /*
  * C entry point for a secondary processor.
  */
-asmlinkage void __init smp_callin(void)
+asmlinkage __visible void __init smp_callin(void)
 {
 	struct mm_struct *mm = &init_mm;
 

arch/riscv/kernel/traps.c

@@ -84,7 +84,7 @@ static void do_trap_error(struct pt_regs *regs, int signo, int code,
 }
 
 #define DO_ERROR_INFO(name, signo, code, str)				\
-asmlinkage void name(struct pt_regs *regs)				\
+asmlinkage __visible void name(struct pt_regs *regs)			\
 {									\
 	do_trap_error(regs, signo, code, regs->sepc, "Oops - " str);	\
 }
@@ -121,7 +121,7 @@ static inline unsigned long get_break_insn_length(unsigned long pc)
 	return (((insn & __INSN_LENGTH_MASK) == __INSN_LENGTH_32) ? 4UL : 2UL);
 }
 
-asmlinkage void do_trap_break(struct pt_regs *regs)
+asmlinkage __visible void do_trap_break(struct pt_regs *regs)
 {
 	if (user_mode(regs))
 		force_sig_fault(SIGTRAP, TRAP_BRKPT, (void __user *)regs->sepc);