Re: [PATCH v4 3.0-rc2-tip 2/22] 2: uprobes: Breakground page replacement.

Srikar Dronamraju
2011-06-13T09:07:38Z

* Peter Zijlstra <peterz@infradead.org> [2011-06-10 01:03:29]:

> On Tue, 2011-06-07 at 18:28 +0530, Srikar Dronamraju wrote:
> > + vaddr_old = kmap_atomic(old_page, KM_USER0);
> > + vaddr_new = kmap_atomic(new_page, KM_USER1);
> > +
> > + memcpy(vaddr_new, vaddr_old, PAGE_SIZE);
> > + /* poke the new insn in, ASSUMES we don't cross page boundary */
> > + addr = vaddr;
> > + vaddr &= ~PAGE_MASK;
> > + memcpy(vaddr_new + vaddr, &opcode, uprobe_opcode_sz);
> > +
> > + kunmap_atomic(vaddr_new);
> > + kunmap_atomic(vaddr_old);
>
>
> > + vaddr_new = kmap_atomic(page, KM_USER0);
> > + vaddr &= ~PAGE_MASK;
> > + memcpy(opcode, vaddr_new + vaddr, uprobe_opcode_sz);
> > + kunmap_atomic(vaddr_new);
> >

>
> Both sequences in resp {write,read}_opcode() assume the opcode doesn't
> cross page boundaries but don't in fact have any assertions validating
> this assumption.
>

read_opcode and write_opcode reads/writes just one breakpoint instruction
I had the below note just above the write_opcode definition.

/*
* NOTE:
* Expect the breakpoint instruction to be the smallest size instruction for
* the architecture. If an arch has variable length instruction and the
* breakpoint instruction is not of the smallest length instruction
* supported by that architecture then we need to modify read_opcode /
* write_opcode accordingly. This would never be a problem for archs that
* have fixed length instructions.
*/

Do we have archs which have a breakpoint instruction which isnt of the
smallest instruction size for that arch. If we do have can we change the
write_opcode/read_opcode while we support that architecture?

--
Thanks and Regards
Srikar
>
>