llvm dev - Oct 2014 - [LLVMdev] Emit a jump instruction to a place inside basicblock

On Thu, Oct 30, 2014 at 2:33 PM, Robin Morisset <morisset at google.com>
wrote:
> Hi,
>
> From my understanding of the LLVM IR, it is impossible to jump to the
> middle of a Basic Block, only to its beginning. But there is a
> splitBasicBlock function that seems like it might be useful to you, to make
> sure a basic block is starting at the exact place you want to jump.
>
> Best regards,
> Robin
>
Thanks you all! I'm looking at splitBasicBlock and trying to use that.
BTW, is there a way at lower level of LLVM that can implement this
functionality? E.g. MCBasicBlock or MCInst?

Sincerely,
Xiaoguang
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20141030/78d378da/attachment.html>

On Thu Oct 30 2014 at 1:16:38 PM Xiaoguang Wang <xgwang09 at gmail.com>
wrote:
> On Thu, Oct 30, 2014 at 2:33 PM, Robin Morisset <morisset at
google.com>
> wrote:
>
>> Hi,
>>
>> From my understanding of the LLVM IR, it is impossible to jump to the
>> middle of a Basic Block, only to its beginning. But there is a
>> splitBasicBlock function that seems like it might be useful to you, to
make
>> sure a basic block is starting at the exact place you want to jump.
>>
>> Best regards,
>> Robin
>>
>
> Thanks you all! I'm looking at splitBasicBlock and trying to use that.
> BTW, is there a way at lower level of LLVM that can implement this
> functionality? E.g. MCBasicBlock or MCInst?
>
>
You are unlikely to want to do this at the MC level, maybe the MI level.
What are you trying to accomplish?

-eric
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20141030/ffed0ca6/attachment.html>

On Thu, Oct 30, 2014 at 4:48 PM, Eric Christopher <echristo at gmail.com>
wrote:
>
>
> On Thu Oct 30 2014 at 1:16:38 PM Xiaoguang Wang <xgwang09 at
gmail.com>
> wrote:
>
>> On Thu, Oct 30, 2014 at 2:33 PM, Robin Morisset <morisset at
google.com>
>> wrote:
>>
>>> Hi,
>>>
>>> From my understanding of the LLVM IR, it is impossible to jump to
the
>>> middle of a Basic Block, only to its beginning. But there is a
>>> splitBasicBlock function that seems like it might be useful to you,
to make
>>> sure a basic block is starting at the exact place you want to jump.
>>>
>>> Best regards,
>>> Robin
>>>
>>
>> Thanks you all! I'm looking at splitBasicBlock and trying to use
that.
>> BTW, is there a way at lower level of LLVM that can implement this
>> functionality? E.g. MCBasicBlock or MCInst?
>>
>>
> You are unlikely to want to do this at the MC level, maybe the MI level.
> What are you trying to accomplish?
>
> -eric
>
Thanks for the answer. I want to construct a table which can jump to the
address after a call instruction. And replace the call/ret instructions
with that indirection table. So to protect return address on stack.

Sincerely,
Xiaoguang
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20141030/15105541/attachment.html>