[mhiramat:topic/fprobe-on-fgraph 18/19] arch/arm64/kernel/ftrace.c:147:15: warning: no previous prototype for function 'arch_ftrace_get_symaddr'

[kernel test robot <lkp@intel.com>]

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/mhiramat/linux.git topic/fprobe-on-fgraph
head:   e6369db4372d722c47a45887eeb6a0f483c20ced
commit: e01d449c6f4e427bd6a67f3c1eee29f46ac59770 [18/19] ftrace: Add ftrace_get_symaddr to convert fentry_ip to symaddr
config: arm64-randconfig-001-20241206 (https://download.01.org/0day-ci/archive/20241206/202412061804.5VRzF14E-lkp@intel.com/config)
compiler: clang version 14.0.6 (https://github.com/llvm/llvm-project f28c006a5895fc0e329fe15fead81e37457cb1d1)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20241206/202412061804.5VRzF14E-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202412061804.5VRzF14E-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> arch/arm64/kernel/ftrace.c:147:15: warning: no previous prototype for function 'arch_ftrace_get_symaddr' [-Wmissing-prototypes]
   unsigned long arch_ftrace_get_symaddr(unsigned long fentry_ip)
                 ^
   arch/arm64/kernel/ftrace.c:147:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
   unsigned long arch_ftrace_get_symaddr(unsigned long fentry_ip)
   ^
   static 
   1 warning generated.


vim +/arch_ftrace_get_symaddr +147 arch/arm64/kernel/ftrace.c

   145	
   146	/* Convert fentry_ip to the symbol address without kallsyms */
 > 147	unsigned long arch_ftrace_get_symaddr(unsigned long fentry_ip)
   148	{
   149		u32 insn;
   150	
   151		/*
   152		 * When using patchable-function-entry without pre-function NOPS, ftrace
   153		 * entry is the address of the first NOP after the function entry point.
   154		 *
   155		 * The compiler has either generated:
   156		 *
   157		 * func+00:	func:	NOP		// To be patched to MOV X9, LR
   158		 * func+04:		NOP		// To be patched to BL <caller>
   159		 *
   160		 * Or:
   161		 *
   162		 * func-04:		BTI	C
   163		 * func+00:	func:	NOP		// To be patched to MOV X9, LR
   164		 * func+04:		NOP		// To be patched to BL <caller>
   165		 *
   166		 * The fentry_ip is the address of `BL <caller>` which is at `func + 4`
   167		 * bytes in either case.
   168		 */
   169		if (!IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS))
   170			return fentry_ip - AARCH64_INSN_SIZE;
   171	
   172		/*
   173		 * When using patchable-function-entry with pre-function NOPs, BTI is
   174		 * a bit different.
   175		 *
   176		 * func+00:	func:	NOP		// To be patched to MOV X9, LR
   177		 * func+04:		NOP		// To be patched to BL <caller>
   178		 *
   179		 * Or:
   180		 *
   181		 * func+00:	func:	BTI	C
   182		 * func+04:		NOP		// To be patched to MOV X9, LR
   183		 * func+08:		NOP		// To be patched to BL <caller>
   184		 *
   185		 * The fentry_ip is the address of `BL <caller>` which is at either
   186		 * `func + 4` or `func + 8` depends on whether there is a BTI.
   187		 */
   188	
   189		/* If there is no BTI, the func address should be one instruction before. */
   190		if (!IS_ENABLED(CONFIG_ARM64_BTI_KERNEL))
   191			return fentry_ip - AARCH64_INSN_SIZE;
   192	
   193		/* We want to be extra safe in case entry ip is on the page edge,
   194		 * but otherwise we need to avoid get_kernel_nofault()'s overhead.
   195		 */
   196		if ((fentry_ip & ~PAGE_MASK) < AARCH64_INSN_SIZE * 2) {
   197			if (get_kernel_nofault(insn, (u32 *)(fentry_ip - AARCH64_INSN_SIZE * 2)))
   198				return 0;
   199		} else {
   200			insn = *(u32 *)(fentry_ip - AARCH64_INSN_SIZE * 2);
   201		}
   202	
   203		if (aarch64_insn_is_bti(le32_to_cpu((__le32)insn)))
   204			return fentry_ip - AARCH64_INSN_SIZE * 2;
   205	
   206		return fentry_ip - AARCH64_INSN_SIZE;
   207	}
   208	

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