Subject: [PATCH v4 2/3] arm64: split syscall_trace() into separate functions for enter/exit

From: [email-masked] (AKASHI Takahiro)
Date: Sat, 15 Mar 2014 01:51:51 +0900

On 03/14/2014 03:41 AM, Will Deacon wrote:
> On Thu, Mar 13, 2014 at 10:11:30AM +0000, AKASHI Takahiro wrote:
>> As done in arm, this change makes it easy to confirm we invoke syscall
>> related hooks, including syscall tracepoint, audit and seccomp which would
>> be implemented later, in correct order. That is, undoing operations in the
>> opposite order on exit that they were done on entry.
>>
>> Signed-off-by: AKASHI Takahiro <[email-masked]>
>> ---
>>   arch/arm64/kernel/entry.S  |   10 ++++-----
>>   arch/arm64/kernel/ptrace.c |   48 ++++++++++++++++++++++++++++++++++----------
>>   2 files changed, 41 insertions(+), 17 deletions(-)
>
> [...]
>
>> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
>> index 6a8928b..9993a8f 100644
>> --- a/arch/arm64/kernel/ptrace.c
>> +++ b/arch/arm64/kernel/ptrace.c
>> @@ -1058,29 +1058,27 @@ long arch_ptrace(struct task_struct *child, long request,
>>   	return ptrace_request(child, request, addr, data);
>>   }
>>
>> -asmlinkage int syscall_trace(int dir, struct pt_regs *regs)
>> +asmlinkage int syscall_trace_enter(struct pt_regs *regs)
>>   {
>>   	unsigned long saved_reg;
>>
>>   	if (!test_thread_flag(TIF_SYSCALL_TRACE))
>>   		return regs->syscallno;
>>
>> +	/*
>> +	 * A scrach register (ip(r12) on AArch32, x7 on AArch64) is
>> +	 * used to denote syscall entry/exit:
>> +	 *   0 -> entry
>> +	 */
>
> You could add an enum, like we have on ARM (ptrace_syscall_dir) for the two
> directions.
>
>>   	if (is_compat_task()) {
>> -		/* AArch32 uses ip (r12) for scratch */
>>   		saved_reg = regs->regs[12];
>> -		regs->regs[12] = dir;
>> +		regs->regs[12] = 0;
>>   	} else {
>> -		/*
>> -		 * Save X7. X7 is used to denote syscall entry/exit:
>> -		 *   X7 = 0 -> entry, = 1 -> exit
>> -		 */
>>   		saved_reg = regs->regs[7];
>> -		regs->regs[7] = dir;
>> +		regs->regs[7] = 0;
>
> This code could also be refactored so we calculated the register number
> once, then avoid the if (is_compact_task()) check all over the place.
>
> Similarly on the exit path.

OK, I will implement tracehook_report_syscall() as in arm.

-Takahiro AKASHI

> Will