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Subject[tip:x86/entry 23/80] arch/x86/entry/common.c:234:24: warning: no previous prototype for function 'prepare_exit_to_usermode'
tree:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86/entry
head: 095b7a3e7745e6fb7cf0a1c09967c4f43e76f8f4
commit: aa9712e07f82a5458f2f16c100c491d736240d60 [23/80] x86/entry/common: Protect against instrumentation
config: x86_64-allyesconfig (attached as .config)
compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project e6658079aca6d971b4e9d7137a3a2ecbc9c34aec)
reproduce:
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# install x86_64 cross compiling tool for clang build
# apt-get install binutils-x86-64-linux-gnu
git checkout aa9712e07f82a5458f2f16c100c491d736240d60
# save the attached .config to linux build tree
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=x86_64

If you fix the issue, kindly add following tag as appropriate
Reported-by: kbuild test robot <lkp@intel.com>

All warnings (new ones prefixed by >>, old ones prefixed by <<):

>> arch/x86/entry/common.c:234:24: warning: no previous prototype for function 'prepare_exit_to_usermode' [-Wmissing-prototypes]
__visible noinstr void prepare_exit_to_usermode(struct pt_regs *regs)
^
arch/x86/entry/common.c:234:19: note: declare 'static' if the function is not intended to be used outside of this translation unit
__visible noinstr void prepare_exit_to_usermode(struct pt_regs *regs)
^
static
>> arch/x86/entry/common.c:296:24: warning: no previous prototype for function 'syscall_return_slowpath' [-Wmissing-prototypes]
__visible noinstr void syscall_return_slowpath(struct pt_regs *regs)
^
arch/x86/entry/common.c:296:19: note: declare 'static' if the function is not intended to be used outside of this translation unit
__visible noinstr void syscall_return_slowpath(struct pt_regs *regs)
^
static
2 warnings generated.

vim +/prepare_exit_to_usermode +234 arch/x86/entry/common.c

233
> 234 __visible noinstr void prepare_exit_to_usermode(struct pt_regs *regs)
235 {
236 instrumentation_begin();
237 __prepare_exit_to_usermode(regs);
238 instrumentation_end();
239 exit_to_user_mode();
240 }
241
242 #define SYSCALL_EXIT_WORK_FLAGS \
243 (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
244 _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT)
245
246 static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags)
247 {
248 bool step;
249
250 audit_syscall_exit(regs);
251
252 if (cached_flags & _TIF_SYSCALL_TRACEPOINT)
253 trace_sys_exit(regs, regs->ax);
254
255 /*
256 * If TIF_SYSCALL_EMU is set, we only get here because of
257 * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP).
258 * We already reported this syscall instruction in
259 * syscall_trace_enter().
260 */
261 step = unlikely(
262 (cached_flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU))
263 == _TIF_SINGLESTEP);
264 if (step || cached_flags & _TIF_SYSCALL_TRACE)
265 tracehook_report_syscall_exit(regs, step);
266 }
267
268 static void __syscall_return_slowpath(struct pt_regs *regs)
269 {
270 struct thread_info *ti = current_thread_info();
271 u32 cached_flags = READ_ONCE(ti->flags);
272
273 CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
274
275 if (IS_ENABLED(CONFIG_PROVE_LOCKING) &&
276 WARN(irqs_disabled(), "syscall %ld left IRQs disabled", regs->orig_ax))
277 local_irq_enable();
278
279 rseq_syscall(regs);
280
281 /*
282 * First do one-time work. If these work items are enabled, we
283 * want to run them exactly once per syscall exit with IRQs on.
284 */
285 if (unlikely(cached_flags & SYSCALL_EXIT_WORK_FLAGS))
286 syscall_slow_exit_work(regs, cached_flags);
287
288 local_irq_disable();
289 __prepare_exit_to_usermode(regs);
290 }
291
292 /*
293 * Called with IRQs on and fully valid regs. Returns with IRQs off in a
294 * state such that we can immediately switch to user mode.
295 */
> 296 __visible noinstr void syscall_return_slowpath(struct pt_regs *regs)
297 {
298 instrumentation_begin();
299 __syscall_return_slowpath(regs);
300 instrumentation_end();
301 exit_to_user_mode();
302 }
303

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
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