llvm dev - Nov 2019 - Writing a Pass in LLVM MC (Machine Code) level to Analyze Assembly Code

Llvm-mctoll will raise a binary back to LLVM IR.
Not exactly what you want but it might be something you can leverage.

https://github.com/microsoft/llvm-mctoll

On Mon, Nov 25, 2019 at 1:19 PM Nicolai Hähnle via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> On Thu, Nov 21, 2019 at 3:37 AM Lele Ma via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
> > My goal is to write LLVM Machine IR (MIR) passes to analyze the
assembly
> source code. But it seems I need to find a way to translate the handwritten
> assembly code into MIR format first.
> >
> > Is there any materials, or any modules in LLVM source code, that can
> help to translate assembly code into LLVM MIR for analysis?
> >
> > Or is there any easier ways to analyze assembly code in MIR passes
> without translating it?
>
> MachineIR is designed for code generation, not for general assembly
> representation. MIR is even not necessarily able to represent all
> assembly instructions that a target's hardware supports. The
> disassembler produces MCInsts, and if you wanted to go from there back
> to MachineIR, you'd have to write your own target-specific code to do
> so.
>
> Cheers,
> Nicolai
>
>
>
> >
> > Best Regards,
> > Lele Ma
> >
> >
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
>
> --
> Lerne, wie die Welt wirklich ist,
> aber vergiss niemals, wie sie sein sollte.
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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Thank you for the instructions, Aaron and Nicolai!

Raising a binary to LLVM IR, or raising to MIR is a reasonable solution for
me. However, given Nicolai's information that not all target-specific
instructions are representable in MIR, I got two questions that need your
help:

1. Why MIR does not necessarily represent all target specific instructions
for certain hardware? If someone added those support, will this violate
some design principles of MIR?

2. Instead of IR/MIR raising, I am wondering whether a third path is
possible to solve the problem of analyzing assembly code:
*    - write simple LLVM pass in the `MC` layer to process information not
available in MIR/IR and *
*    - passing analysis result from IR/MIR pass to the MC layer pass where
we can enhance the result with missing representations.*
So the second question is whether it is possible to write passes directly
in the MC layer? If so, is there any documentation or example for that?


Thank you in advance!

Best Regards,
Lele


On Mon, Nov 25, 2019 at 9:15 AM Aaron Smith <aaron.lee.smith at gmail.com>
wrote:
> Llvm-mctoll will raise a binary back to LLVM IR.
> Not exactly what you want but it might be something you can leverage.
>
> https://github.com/microsoft/llvm-mctoll
>
> On Mon, Nov 25, 2019 at 1:19 PM Nicolai Hähnle via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> On Thu, Nov 21, 2019 at 3:37 AM Lele Ma via llvm-dev
>> <llvm-dev at lists.llvm.org> wrote:
>> > My goal is to write LLVM Machine IR (MIR) passes to analyze the
>> assembly source code. But it seems I need to find a way to translate
the
>> handwritten assembly code into MIR format first.
>> >
>> > Is there any materials, or any modules in LLVM source code, that
can
>> help to translate assembly code into LLVM MIR for analysis?
>> >
>> > Or is there any easier ways to analyze assembly code in MIR passes
>> without translating it?
>>
>> MachineIR is designed for code generation, not for general assembly
>> representation. MIR is even not necessarily able to represent all
>> assembly instructions that a target's hardware supports. The
>> disassembler produces MCInsts, and if you wanted to go from there back
>> to MachineIR, you'd have to write your own target-specific code to
do
>> so.
>>
>> Cheers,
>> Nicolai
>>
>>
>>
>> >
>> > Best Regards,
>> > Lele Ma
>> >
>> >
>> > _______________________________________________
>> > LLVM Developers mailing list
>> > llvm-dev at lists.llvm.org
>> > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>>
>>
>> --
>> Lerne, wie die Welt wirklich ist,
>> aber vergiss niemals, wie sie sein sollte.
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>
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Hi All,

A self-follow up and rephrase of my previous question with updated subject:

What I want to do is to analyze hand-written assembly code with 'full
details' where semantics of each instruction can be known in LLVM passes.
Many of such instructions have no corresponding counterparts in IR/MIR
forms, such as 'syscall' 'iret', etc. At MC level, such assembly
code can
be translated to MCInst easily since this level is closest to the assembly
code. Therefore, I am thinking to write a pass at MC level instead of
IR/MIR.

However, when I am searching to learn the MC level passes, I cannot find
any related classes in LLVM infrastructure (such as FunctionPass at IR
level; MachineFunctionPass at MIR pass). Could anyone direct me where I
should start to write a MC level pass?

Best Regards,
Lele


On Mon, Nov 25, 2019 at 5:24 PM Lele Ma <lelema.cn at gmail.com> wrote:
> Thank you for the instructions, Aaron and Nicolai!
>
> Raising a binary to LLVM IR, or raising to MIR is a reasonable solution
> for me. However, given Nicolai's information that not all
target-specific
> instructions are representable in MIR, I got two questions that need your
> help:
>
> 1. Why MIR does not necessarily represent all target specific instructions
> for certain hardware? If someone added those support, will this violate
> some design principles of MIR?
>
> 2. Instead of IR/MIR raising, I am wondering whether a third path is
> possible to solve the problem of analyzing assembly code:
> *    - write simple LLVM pass in the `MC` layer to process information not
> available in MIR/IR and *
> *    - passing analysis result from IR/MIR pass to the MC layer pass where
> we can enhance the result with missing representations.*
> So the second question is whether it is possible to write passes directly
> in the MC layer? If so, is there any documentation or example for that?
>
>
> Thank you in advance!
>
> Best Regards,
> Lele
>
>
> On Mon, Nov 25, 2019 at 9:15 AM Aaron Smith <aaron.lee.smith at
gmail.com>
> wrote:
>
>> Llvm-mctoll will raise a binary back to LLVM IR.
>> Not exactly what you want but it might be something you can leverage.
>>
>> https://github.com/microsoft/llvm-mctoll
>>
>> On Mon, Nov 25, 2019 at 1:19 PM Nicolai Hähnle via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>>> On Thu, Nov 21, 2019 at 3:37 AM Lele Ma via llvm-dev
>>> <llvm-dev at lists.llvm.org> wrote:
>>> > My goal is to write LLVM Machine IR (MIR) passes to analyze
the
>>> assembly source code. But it seems I need to find a way to
translate the
>>> handwritten assembly code into MIR format first.
>>> >
>>> > Is there any materials, or any modules in LLVM source code,
that can
>>> help to translate assembly code into LLVM MIR for analysis?
>>> >
>>> > Or is there any easier ways to analyze assembly code in MIR
passes
>>> without translating it?
>>>
>>> MachineIR is designed for code generation, not for general assembly
>>> representation. MIR is even not necessarily able to represent all
>>> assembly instructions that a target's hardware supports. The
>>> disassembler produces MCInsts, and if you wanted to go from there
back
>>> to MachineIR, you'd have to write your own target-specific code
to do
>>> so.
>>>
>>> Cheers,
>>> Nicolai
>>>
>>>
>>>
>>> >
>>> > Best Regards,
>>> > Lele Ma
>>> >
>>> >
>>> > _______________________________________________
>>> > LLVM Developers mailing list
>>> > llvm-dev at lists.llvm.org
>>> > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
>>>
>>>
>>> --
>>> Lerne, wie die Welt wirklich ist,
>>> aber vergiss niemals, wie sie sein sollte.
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org
>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
>>
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