Discussion on toolchain support for reliable stacktracing at LPC 2022

Discussion on toolchain support for reliable stacktracing at LPC 2022

[Indu Bhagat]

Hello,

What do you think about the following activity at the LPC Plumbers 2022 
@ Toolchains and Kernel track ?

Title:
Toolchain support for reliable stack tracing in the Linux kernel

Abstract:
The Linux kernel uses a two fold approach for its stack unwinding needs
  -- ORC: the kernel's stack unwinding format
  -- objtool: a tool to generate the unwind information by 
post-processing the generated binaries

For reliable stack traces, correct and complete metadata is only one of 
the pillars. The purpose of this discussion is to brainstorm the 
additional components  that are required in the form of toolchain 
support for assisting the kernel's requirement of reliable stack traces.

Earlier at LPC 2021, we talked about the proposal to define and generate 
CTF Frame unwind information in the GNU Toolchain, and also in another 
session, the issues with objtool on arm64. In this session, we plan to 
converge these discussions with a perspective of what toolchain support 
can be provided to support objtool in the Linux kernel to begin with.

Participants: Indu Bhagat, Josh Poimboeuf, anyone else ?

I am looking at the material Mark sent (in another thread) and the 
pointers in objtool session slides (from LPC 2021) meanwhile. If you 
have suggestions to refine the abstract with more detailed content, that 
will be welcome too.

Thanks
Indu

Re: Discussion on toolchain support for reliable stacktracing at LPC 2022

[Indu Bhagat]

On 6/23/22 10:34 AM, Indu Bhagat wrote:
> Hello,
> 
> What do you think about the following activity at the LPC Plumbers 2022 
> @ Toolchains and Kernel track ?
> 
> Title:
> Toolchain support for reliable stack tracing in the Linux kernel
> 
> Abstract:
> The Linux kernel uses a two fold approach for its stack unwinding needs
>   -- ORC: the kernel's stack unwinding format
>   -- objtool: a tool to generate the unwind information by 
> post-processing the generated binaries
> 
> For reliable stack traces, correct and complete metadata is only one of 
> the pillars. The purpose of this discussion is to brainstorm the 
> additional components  that are required in the form of toolchain 
> support for assisting the kernel's requirement of reliable stack traces.
> 
> Earlier at LPC 2021, we talked about the proposal to define and generate 
> CTF Frame unwind information in the GNU Toolchain, and also in another 
> session, the issues with objtool on arm64. In this session, we plan to 
> converge these discussions with a perspective of what toolchain support 
> can be provided to support objtool in the Linux kernel to begin with.
> 
> Participants: Indu Bhagat, Josh Poimboeuf, anyone else ?
> 
> I am looking at the material Mark sent (in another thread) and the 
> pointers in objtool session slides (from LPC 2021) meanwhile. If you 
> have suggestions to refine the abstract with more detailed content, that 
> will be welcome too.
> 
> Thanks
> Indu

Josh suggested we change the scope of the discussion to objtool. So, I 
have updated the Title/Abstract as follows:

Title: Toolchain support for objtool in the Linux kernel

Abstract:
The Linux kernel relies on objtool for performing a host of validations, 
metadata generation, and other fixups and annotations. One of Objtool's 
feature is stack metadata validation and generation which forms the 
backbone of kernel's reliable stack unwinding needs.

In this session, we will discuss what components of the objtool, in 
general, can get some help from the toolchain. We will also discuss what 
assistance can be provided for the usecase of reliable stack tracing. 
For reliable stack traces, correct and complete metadata is only one of 
the pillars. We will discuss the additional components that are 
required. At LPC 2021, we talked about the proposal to define and 
generate CTF Frame unwind information in the GNU Toolchain. There was 
also a discussion on objtool on arm64. In this session, we plan to 
converge these discussions with a perspective of what toolchain support 
can be provided to support objtool in the Linux kernel.