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SubjectRe: [PATCH v2 05/13] uprobes: add arch write opcode hook
On 10/19/13 12:50, Oleg Nesterov wrote:
> On 10/15, David Long wrote:
>>
>> Allow arches to write the opcode with a custom function. ARM needs to
>> customize the swbp instruction depending on the condition code of the
>> instruction it replaces.
>
> Well, we already have "__weak set_swbp(auprobe, ...)", can't arm use it?
>
> If not,
>
>> +void __weak arch_uprobe_write_opcode(struct arch_uprobe *auprobe, void *vaddr,
>> + uprobe_opcode_t opcode)
>> +{
>> + memcpy(vaddr, &opcode, UPROBE_SWBP_INSN_SIZE);
>> +}
>> ...
>> - copy_to_page(new_page, vaddr, &opcode, UPROBE_SWBP_INSN_SIZE);
>> + vaddr_new = kmap_atomic(new_page);
>> + arch_uprobe_write_opcode(auprobe, vaddr_new + (vaddr & ~PAGE_MASK),
>> + opcode);
>> + kunmap_atomic(vaddr_new);
>
> Again, if you need to add the new __weak helper, I think it should simply
> do copy_to_page().
>
> Oleg.
>

Unfortunately, providing an alternative set_swbp() would mean
duplicating a moderate chunk of code from kernel/uprobes.c. Adding
arch_uprobe_write_opcode() feels a little more like the right thing to
do to me. I notice there don't seem to be any alternative set_swbp
functions in the (rc6) kernel tree. I will adjust the
arch_uprobe_write_opcode imlementation as suggested.

-dl



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