syscall trace at kernel land

[Dave Hylands]

Hi Rajat,

On Tue, Jan 11, 2011 at 2:10 AM, Rajat Sharma <fs.rajat at gmail.com> wrote:
>> is there any procedure in kernel to check for the interrupt vector number which caused it to be invoked?
> Its actually very architecture dependent, on x86, its 'int $0x80'
> which causes user space to call system calls handlers. Recent intel
> architectures have callgate mechanism to enter into system call, look
> for sysenter instruction.
> Anyways, are you interested in interrupt number or the system call number?
>
>> i mean like one of my friends said that when  kernel is about to restart a
>> syscall then it raises signal -ERESTARTSYS signal for signal handler.
>
> Thats totally wrong. Like any other error code, its just an error code
> which waiting API return if process was interrupted while waiting on
> semaphore, e.g.

On the ARM platform, at least, if a syscall (like ioctl) returns
-ERESTARTSYS, then the ioctl will be reissued after the signal handler
runs.

I know this to be true, as I've verified it's functionality
emperically. This is further supported by the kernel documentation
http://lxr.linux.no/linux+v2.6.37/Documentation/DocBook/kernel-hacking.tmpl#L346

Dave Hylands