Re: Possible bug on signal.h

["Jordi Brínquez" <jordi.brinquez@gmail.com>]

I'm trying to modify UML so I'm using kernel headers

but anyway there is a problem on sigaction definition on signal.h

Jordi



linux-os wrote:

> On Thu, 24 Feb 2005, Jordi Brinquez wrote:
>
>> Hi,
>>
>> I think I found a possible bug on file signal.h.
>>
>> The problem comes when you define a struct sigaction on a user program
>> and then you use the function sigaction to remap a signal handler (in
>> my case a page_fault) for my own function, this system call is
>> compiled as __NR_sigaction system call (by default this routine is
>> managed by sys_sigaction routine) and if the architecture defines
>> __ARCH_WANT_SYS_RT_SIGACTION kernel uses the routine sys_rt_sigaction
>> on the file kernel/signal.c that instead of copying the fields from
>> one structure to the other it just uses copy_from_user and
>> copy_to_user with the consequent mess with the fields.
>>
>
> You NEVER use kernel headers for user code.... EVER. If you
> are making something strange, like as you said a page-fault
> handler, then you make an in-kernel driver (module).
>
> FYI, no page-fault handler could ever work in user-mode
> anyway. A page-fault occurs because the user accesses some
> page it doesn't own (probably because it isn't in memory).
> The kernel page-fault handler checks to see if the page was
> promised. If not, it terminates the user-mode task with
> a signal. If so, it finds some free page or makes one
> available and maps it into the user's address-space before
> returning control to the user. Since the user doesn't own
> any free pages, it can't map in any.
>
>
> [SNIPPED...]
>
>
> Cheers,
> Dick Johnson
> Penguin : Linux version 2.6.10 on an i686 machine (5537.79 BogoMips).
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