llvm dev - Jul 2021 - CFG with x86 basic blocks

Hello,

Is there a way to use LLVM and clang++ to generate a Control Flow Graph
with x86 basic blocks?

I am able to generate control flow graphs using clang++ and LLVM's opt, but
the CFG's basic blocks contain LLVM IR. Instead, I would like the basic
blocks to contain x86 assembly.

Ideally this tool would be useful for visualizing optimization passes that
a compiler makes to the code and ultimately the assembly.

Thanks!

Olivia

--
Olivia Weng
PhD Student
Computer Science and Engineering
University of California, San Diego
https://oliviaweng.com <https://www.oliviaweng.com>
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On 2021-07-27, Olivia Weng via llvm-dev wrote:
>Hello,
>
>Is there a way to use LLVM and clang++ to generate a Control Flow Graph
>with x86 basic blocks?
>
>I am able to generate control flow graphs using clang++ and LLVM's opt,
but
>the CFG's basic blocks contain LLVM IR. Instead, I would like the basic
>blocks to contain x86 assembly.
>
>Ideally this tool would be useful for visualizing optimization passes that
>a compiler makes to the code and ultimately the assembly.
>
>Thanks!
>
>Olivia
I don't think there is a direct tool in llvm. But the default clang -S
output
(-fverbose-asm) is actually not too bad. You can find labels for machine basic
blocks.

Some reverse engineering tools (e.g. radare2) have pretty viewers.

It is possible to view the control-flow graphs of Machine IR in LLVM, which much
more approximates machine code. However, there is no way that I am aware of to
get a CFG containing machine IR displayed from the command line; you have to
inject calls to MachineFunction::viewCFG manually (which requires a debug
build).

As Fangrui points out, there are other reverse engineering tools that can turn
an assembly function into a graphical view of basic blocks. All of the standard
disassemblers (IDA, BinaryNinja, Radare2/cutter, Ghidra) should be capable of
this task. Hooking up your own hacky script to build a graphical view given an
assembly file or object file as input is not a challenging task (unless you want
to support the variety of ways switch tables are emitted).

From: llvm-dev <llvm-dev-bounces at lists.llvm.org> On Behalf Of Olivia
Weng via llvm-dev
Sent: Tuesday, July 27, 2021 18:18
To: llvm-dev at lists.llvm.org
Subject: [llvm-dev] CFG with x86 basic blocks

Hello,

Is there a way to use LLVM and clang++ to generate a Control Flow Graph with x86
basic blocks?

I am able to generate control flow graphs using clang++ and LLVM's opt, but
the CFG's basic blocks contain LLVM IR. Instead, I would like the basic
blocks to contain x86 assembly.

Ideally this tool would be useful for visualizing optimization passes that a
compiler makes to the code and ultimately the assembly.

Thanks!

Olivia

--
Olivia Weng
PhD Student
Computer Science and Engineering
University of California, San Diego
https://oliviaweng.com<https://www.oliviaweng.com>
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