Re: Catching signals in a Kernel Module?

Alan Cox (alan@lxorguk.ukuu.org.uk)
Thu, 12 Aug 1999 19:43:48 +0100 (BST)

> my module working. However, when a user tries to read or
> write an unsupported MSR, the Intel Pentium II returns with a GP(0).
> This causes my module to die with a SEGV.
>
> How can I catch this signal within my module? I have

Be careful about signal versus exception. Signal has a specific meaning in
Unix that is different.

> the Linux Device Drivers book, but it doesn't
> appear to cover this type of problem.

I'm not suprised 8). You can do this. The best example of it is the
copy_*_user functions (include/asm-i386/uaccess.h)

You want the asm code to look like

1: wrmsr blah
2:
.section .fixup, "ax"
3: code to handle fault
jmp 2b # Back to the original code path
.previous
.section __ex_table, "a"
.align 4
.long 1b,3b
.previous

What happens when you get a fault is the kernel walks the exception table
looking for the fault address (thats the piece in the __ex_table. If it
finds the address it jumps to the fault handler address. If not it
follows the normal path.

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