Re: Possible bug on signal.h

[linux-os]

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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