Page MenuHomePhabricator

Implement DW_CFA_LLVM_* for Heterogeneous Debugging
Needs ReviewPublic

Authored by scott.linder on Mar 26 2020, 12:16 PM.



Add support in MC/MIR for writing/parsing, and DebugInfo.

Diff Detail

Event Timeline

scott.linder created this revision.Mar 26 2020, 12:16 PM

git clang-format

The new operation is defined at @t-tye is working on formatting the proposal to be sent to upstream DWARF as an RFC, and I am working to land these patches as an initial implementation.

Update to match changes in proposal.

Update encodings of DW_OP_CFA_* to avoid conflict with a GNU extension.

scott.linder retitled this revision from Implement DW_CFA_LLVM_def_cfa_aspace to Implement DW_CFA_LLVM_* for Heterogeneous Debugging.
scott.linder edited the summary of this revision. (Show Details)

Update docs for encoding change

RamNalamothu added inline comments.Tue, May 5, 6:33 AM

Now, maximum number of operands is 3


Emitting DW_CFA_def_aspace_cfa_sf is yet to be handled?

I see that even the emission of DWARF 5 supported DW_CFA_def_cfa_sf and DW_CFA_def_cfa_offset_sf are also yet to be handled.

scott.linder marked 2 inline comments as done.Fri, May 8, 2:51 PM
scott.linder added inline comments.

Thank you, I'll update the patch.


Right, this should probably be a TODO in the code. As the existing _sf variants are not implemented yet either and AMDGPU does not currently require any of them (we always retain a copy of the stack pointer on entry in some form) I didn't implement it here.

Address feedback

arsenm added a subscriber: arsenm.Tue, May 12, 11:51 AM
arsenm added inline comments.

Unrelated change


Unrelated change


Tests missing for the parse errors?

scott.linder marked an inline comment as done.
scott.linder removed a subscriber: arsenm.

Add tests for parse errors, fix formatting


I wish all of this rote mechanical stuff were just automated. Do you have a preference on how I resolve this? The options I'm aware of:

  • I can factor out every clang-format diff into a separate NFC review, but effectively every non-trivial patch would need one, so I would end up having to manage on the order of twice as many Phabricator reviews.
  • I can make one pass at the very end to try to pull all the unrelated NFC formatting changes into one commit, but I would rather do this just before committing so I am not constantly having to comb through every patch in the set trying to clean them up.
  • I can aggressively commit these NFC cleanups as separate patches without reviews as they come up, before posting the actual review.

Or I can lobby on llvm-dev to just lint/format the whole codebase once, and then gate commits on patches not breaking it. This would probably save everyone too much time, and make git blame too useful though.

scott.linder marked an inline comment as done.Wed, May 13, 2:09 PM
dblaikie added inline comments.Wed, May 13, 3:20 PM

Most of it is automated or can be - if you're only clang-formatting the lines of code you've edited, it's usually enough - just in this instance happens to be a very long statement & so it gets reformatted together even if you changed unrelated lines in the statement. /maybe/ clang-format could be modified to not do that (to be able to reformat only the edited lines, rather than the whole statement)

Something like this one - yeah, you could commit that specific formatting (not reformatting the whole file) in advance to ensure the review is simpler/clearer. I think this fits under the general idea of reformatting early if you're making significant changes - like if you're majorly reworking a whole file, it's not uncommon to reformat the whole file. But yeah, if you're touching a statement/block in depth and it's significantly misformatted, easy thing to fix/commit in advance - doesn't need a formal pre-commit review (so long as it's code that's going to be touched/changed soon - don't go reformatting whole files without such motivation, unless they're really egregiously formatted).

scott.linder marked an inline comment as done.Wed, May 13, 4:32 PM
scott.linder added inline comments.

Is there any document with the rationale for why LLVM prefers incrementally massaging code into the canonical format, rather than just fixing the entire codebase at once? Like a section in some docs somewhere, or an old llvm-dev thread? It might make the pill easier to swallow if I understand the ideal to which I'm dedicating time fiddling with it.

Use llvm-readelf for more compact tests

Correct test file names. I missed this when renaming the CFA operation itself
to match the updated proposal.

Harbormaster completed remote builds in B56771: Diff 264061.