Re: [PATCH] arm64: syscall: Ensure saved x0 is kept in-sync with tracer updates

Hi Will,

kernel test robot noticed the following build errors:

[auto build test ERROR on linux-review/Yiqi-Sun/arm64-ptrace-use-live-x0-for-seccomp-and-audit-after-ptrace/20260815-210721]

url:    https://github.com/intel-lab-lkp/linux/commits/Will-Deacon/arm64-syscall-Ensure-saved-x0-is-kept-in-sync-with-tracer-updates/20260815-220235
base:   https://github.com/intel-lab-lkp/linux Yiqi-Sun/arm64-ptrace-use-live-x0-for-seccomp-and-audit-after-ptrace/20260815-210721
patch link:    https://lore.kernel.org/r/20260714143600.23853-1-will%40kernel.org
patch subject: [PATCH] arm64: syscall: Ensure saved x0 is kept in-sync with tracer updates
config: arm64-randconfig-001-20260820 (https://download.01.org/0day-ci/archive/20260820/[email protected]/config)
compiler: clang version 24.0.0git (https://github.com/llvm/llvm-project 935bfc708590c60147a79c7df145bb6e68b1d388)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260820/[email protected]/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 <[email protected]>
| Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/

All errors (new ones prefixed by >>):

>> arch/arm64/kernel/ptrace.c:2461:13: error: conflicting types for 'update_syscall_orig_x0_after_ptrace'
    2461 | static void update_syscall_orig_x0_after_ptrace(struct pt_regs *regs)
         |             ^
   arch/arm64/kernel/ptrace.c:563:13: note: previous definition is here
     563 | static void update_syscall_orig_x0_after_ptrace(struct task_struct *target)
         |             ^
>> arch/arm64/kernel/ptrace.c:2490:39: error: incompatible pointer types passing 'struct pt_regs *' to parameter of type 'struct task_struct *' [-Wincompatible-pointer-types]
    2490 |                 update_syscall_orig_x0_after_ptrace(regs);
         |                                                     ^~~~
   arch/arm64/kernel/ptrace.c:563:69: note: passing argument to parameter 'target' here
     563 | static void update_syscall_orig_x0_after_ptrace(struct task_struct *target)
         |                                                                     ^
   arch/arm64/kernel/ptrace.c:2498:38: error: incompatible pointer types passing 'struct pt_regs *' to parameter of type 'struct task_struct *' [-Wincompatible-pointer-types]
    2498 |         update_syscall_orig_x0_after_ptrace(regs);
         |                                             ^~~~
   arch/arm64/kernel/ptrace.c:563:69: note: passing argument to parameter 'target' here
     563 | static void update_syscall_orig_x0_after_ptrace(struct task_struct *target)
         |                                                                     ^
   3 errors generated.


vim +/update_syscall_orig_x0_after_ptrace +2461 arch/arm64/kernel/ptrace.c

  2460	
> 2461	static void update_syscall_orig_x0_after_ptrace(struct pt_regs *regs)
  2462	{
  2463		/*
  2464		 * Keep orig_x0 authoritative so that seccomp (via
  2465		 * syscall_get_arguments()), audit and the restart path all see the same
  2466		 * first argument the syscall is dispatched with, even if it has been
  2467		 * updated by a tracer. Skip this for NO_SYSCALL (set either by the user
  2468		 * or the tracer), as regs[0] holds the return value (see the comment in
  2469		 * el0_svc_common()) and can be unwound using syscall_rollback().
  2470		 * For compat tasks, orig_r0 is provided directly through GPR index 17.
  2471		 */
  2472		if (!is_compat_task() && regs->syscallno != NO_SYSCALL)
  2473			regs->orig_x0 = regs->regs[0];
  2474	}
  2475	
  2476	int syscall_trace_enter(struct pt_regs *regs)
  2477	{
  2478		unsigned long flags = read_thread_flags();
  2479		int ret;
  2480	
  2481		if (flags & (_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE)) {
  2482			ret = report_syscall_entry(regs);
  2483			if (ret || (flags & _TIF_SYSCALL_EMU))
  2484				return NO_SYSCALL;
  2485	
  2486			/*
  2487			 * Ensure ptrace changes to x0 are visible to seccomp
  2488			 * ptrace exits (SECCOMP_RET_TRACE).
  2489			 */
> 2490			update_syscall_orig_x0_after_ptrace(regs);
  2491		}
  2492	
  2493		/* Do the secure computing after ptrace; failures should be fast. */
  2494		if (secure_computing() == -1)
  2495			return NO_SYSCALL;
  2496	
  2497		/* Ensure seccomp updates to x0 are visible to audit. */
  2498		update_syscall_orig_x0_after_ptrace(regs);
  2499	
  2500		if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
  2501			trace_sys_enter(regs, regs->syscallno);
  2502	
  2503		audit_syscall_entry(regs->syscallno, regs->regs[0], regs->regs[1],
  2504				    regs->regs[2], regs->regs[3]);
  2505	
  2506		return regs->syscallno;
  2507	}
  2508	

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