Add support for SFrame stack trace format

[ibhagatgnu]

SFrame stands for 'Simple FRAME' stack trace format. It expresses the minimal necessary information for stack tracing, namely, the Cannonical Frame Address (CFA), Frame pointer (FP) and the return address (RA). Since 2.40, the GNU Bintuils supports the SFrame stack trace format. It will be great to have the support for the format in LLVM.

Current version of the format is SFrame Version 2. The spec of the (V2) format is published here https://sourceware.org/binutils/docs-2.41/sframe-spec.pdf.

[Endilll]

I'm not sure we have bandwidth to implement this ourselves, but we certainly welcome pull requests.

[Sterling-Augustine]

Still needs quite a bit of work before it can be merged to mainline, but I have a basic prototype for producing sframes in llvm here:

https://github.com/Sterling-Augustine/llvm-project/tree/sframe

I normally use lld to link, and that has hidden a layering violation from MC up to DWARFDebugFrame, but I'm working on refactoring that. It also breaks certain debug info tests for reasons I don't follow.

But it is good enough to pass the gnu gas cfi-sframe.exp tests for x86 (with some small patches, all explained in README.sframe.notes.

[david-xl]

Can the refactoring changes be done independently of the SFrame support?

[Sterling-Augustine]

Can the refactoring changes be done independently of the SFrame support?

That has been my approach. However, my rfc got no response, and I have had to beg to get these changes reviewed. They do seem to have gotten some traction lately though, so that is good.

https://discourse.llvm.org/t/rfc-debuginfo-dwarf-refactor-into-to-lower-and-higher-level-libraries/86665

I believe the last pr before the big move is #143762

[david-xl]

right -- lack of response probably means no concerns, which is a good sign.

[thesamesam]

Just cross-linking things:

• https://discourse.llvm.org/t/rfc-adding-sframe-support-to-llvm/86900
• [BinaryFormat] Add "SFrame" structures and constants #147264
• [Object] Beginnings of SFrame parser and dumper #147294