On 6/12/19 1:32 AM, Naveen N. Rao wrote:
> Paul Clarke wrote:
>> What are the circumstances in which raw_syscalls:sys_exit reports "-1" for
>> the syscall ID?
>>
>> perf 5375 [007] 59632.478528: raw_syscalls:sys_enter: NR 1 (3,
>> 9fb888, 8, 2d83740, 1, 7ffff)
>> perf 5375 [007] 59632.478532: raw_syscalls:sys_exit: NR 1 = 8
>> perf 5375 [007] 59632.478538: raw_syscalls:sys_enter: NR 15 (11,
>> 7ffffca734b0, 7ffffca73380, 2d83740, 1, 7ffff)
>> perf 5375 [007] 59632.478539: raw_syscalls:sys_exit: NR -1 = 8
>> perf 5375 [007] 59632.478543: raw_syscalls:sys_enter: NR 16 (4, 2401,
>> 0, 2d83740, 1, 0)
>> perf 5375 [007] 59632.478551: raw_syscalls:sys_exit: NR 16 = 0
>
> Which architecture?
> For powerpc, see:
>
> static inline int syscall_get_nr(struct task_struct *task, struct pt_regs
> *regs)
> {
> /*
> * Note that we are returning an int here. That means 0xffffffff, ie.
> * 32-bit negative 1, will be interpreted as -1 on a 64-bit kernel.
> * This is important for seccomp so that compat tasks can set r0 = -1
> * to reject the syscall.
> */
> return TRAP(regs) == 0xc00 ? regs->gpr[0] : -1;
> }
So, that's intentional? And has some special meaning? (I confess I don't
understand what the comment is saying exactly.)
Is this documented? Does something depend on this ABI?
To me, it just makes parsing more difficult, both by humans and machines.
PC
