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

:::::: 
:::::: Manual check reason: "low confidence bisect report"
:::::: 

BCC: [email protected]
CC: [email protected]
In-Reply-To: <[email protected]>
References: <[email protected]>
TO: Will Deacon <[email protected]>
TO: [email protected]
CC: [email protected]
CC: Will Deacon <[email protected]>
CC: Kees Cook <[email protected]>
CC: Jinjie Ruan <[email protected]>
CC: Mark Rutland <[email protected]>
CC: Yiqi Sun <[email protected]>
CC: Catalin Marinas <[email protected]>

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
:::::: branch date: 2 days ago
:::::: commit date: 2 days ago
config: arm64-allnoconfig-bpf (https://download.01.org/0day-ci/archive/20260817/[email protected]/config)
compiler: aarch64-linux-gnu-gcc (Debian 14.2.0-19) 14.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260817/[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/r/[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'; have 'void(struct pt_regs *)'
    2461 | static void update_syscall_orig_x0_after_ptrace(struct pt_regs *regs)
         |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   arch/arm64/kernel/ptrace.c:563:13: note: previous definition of 'update_syscall_orig_x0_after_ptrace' with type 'void(struct task_struct *)'
     563 | static void update_syscall_orig_x0_after_ptrace(struct task_struct *target)
         |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


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

3157858feff8919 AKASHI Takahiro 2014-04-30  2460  
f579bf33f3c09c9 Will Deacon     2026-07-14 @2461  static void update_syscall_orig_x0_after_ptrace(struct pt_regs *regs)
f579bf33f3c09c9 Will Deacon     2026-07-14  2462  {
f579bf33f3c09c9 Will Deacon     2026-07-14  2463  	/*
f579bf33f3c09c9 Will Deacon     2026-07-14  2464  	 * Keep orig_x0 authoritative so that seccomp (via
f579bf33f3c09c9 Will Deacon     2026-07-14  2465  	 * syscall_get_arguments()), audit and the restart path all see the same
f579bf33f3c09c9 Will Deacon     2026-07-14  2466  	 * first argument the syscall is dispatched with, even if it has been
f579bf33f3c09c9 Will Deacon     2026-07-14  2467  	 * updated by a tracer. Skip this for NO_SYSCALL (set either by the user
f579bf33f3c09c9 Will Deacon     2026-07-14  2468  	 * or the tracer), as regs[0] holds the return value (see the comment in
f579bf33f3c09c9 Will Deacon     2026-07-14  2469  	 * el0_svc_common()) and can be unwound using syscall_rollback().
f579bf33f3c09c9 Will Deacon     2026-07-14  2470  	 * For compat tasks, orig_r0 is provided directly through GPR index 17.
f579bf33f3c09c9 Will Deacon     2026-07-14  2471  	 */
f579bf33f3c09c9 Will Deacon     2026-07-14  2472  	if (!is_compat_task() && regs->syscallno != NO_SYSCALL)
f579bf33f3c09c9 Will Deacon     2026-07-14  2473  		regs->orig_x0 = regs->regs[0];
f579bf33f3c09c9 Will Deacon     2026-07-14  2474  }
f579bf33f3c09c9 Will Deacon     2026-07-14  2475  

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