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SubjectRe: [PATCH v2 05/13] uprobes: add arch write opcode hook
On 10/23, David Long wrote:
>
> 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.

Yes, yes, sorry for confusion. What I actually tried to suggest is
something like the trivial patch below.

Then arm can do:

uprobe_opcode_t arch_uprobe_swbp_insn(struct arch_uprobe *auprobe)
{
return __opcode_to_mem_arm(auprobe->bpinsn);
}

No?

> I notice there don't seem to be any alternative set_swbp functions
> in the (rc6) kernel tree

Yes... I think we should simply make it "static". And set_orig_insn()
too.

Oleg.

--- x/kernel/events/uprobes.c
+++ x/kernel/events/uprobes.c
@@ -304,6 +304,11 @@ put_old:
return ret;
}

+uprobe_opcode_t __weak arch_uprobe_swbp_insn(struct arch_uprobe *auprobe)
+{
+ return UPROBE_SWBP_INSN;
+}
+
/**
* set_swbp - store breakpoint at a given address.
* @auprobe: arch specific probepoint information.
@@ -315,7 +320,7 @@ put_old:
*/
int __weak set_swbp(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long vaddr)
{
- return write_opcode(mm, vaddr, UPROBE_SWBP_INSN);
+ return write_opcode(mm, vaddr, arch_uprobe_swbp_insn(auprobe));
}

/**


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