[llvm-dev] Adding DWARF5 accelerator table support to llvm

Robinson, Paul via llvm-dev llvm-dev at lists.llvm.org
Wed Jan 17 11:43:24 PST 2018

> -----Original Message-----
> From: Pavel Labath [mailto:labath at google.com]
> Sent: Wednesday, January 17, 2018 8:14 AM
> To: jdevlieghere at apple.com; LLVM Dev; LLDB; David Blaikie; Robinson, Paul
> Subject: Adding DWARF5 accelerator table support to llvm
> Hello all,
> In <https://reviews.llvm.org/D41986#977215> it was brought up that
> there are at least two parties interested in having DWARF5 accelerator
> tables implemented, so I'm writing this email to see if there's anyone
> else interested in this topic, and to try to synchronize our efforts.
> Our interest for this stems from a desire to make dwarf parsing fast
> on non-apple targets (specifically android). As you may know, apple
> targets already use a non-standard accelerator table format, which was
> a precursor to the dwarf5 one. Due to other differences in debug info
> deployment model, the apple tables are not directly applicable to
> other targets, so instead of trying to make them fit, we chose to go
> with the standard approach.
> I personally will have some time to work on this this quarter or two,
> and my plan is roughly the following:
> 1. add .debug_names support to llvm-dwarfdump via the DebugInfo
> library (to enable testing of the table generation)
> 2. add .debug_names generation support (not enabled by default)
> 3. add .debug_names support to lldb
> 4. validate all three things work together
> 5. hook up .debug_names to clang's -glldb flag.
> 6. add .debug_names support to lld (accelerator table merging)
> Right now I have (1) roughly implemented, and I think I'll be able to
> put it up for review in a couple of days (although I expect the review
> will go through several revisions before being accepted). I also have
> a very basic implementation of (2), but this is still quite far from
> being upstreamable.
> So, my question is whether anyone is planning to work, or maybe
> working already on dwarf5 accelerator tables? Help with reviewing
> patches would also be greatly appreciated. If you have any questions
> or concerns, let me know.

Hi Pavel,
This would not interfere/duplicate anything Sony is doing in the near
future.  I think having the accelerator tables available for our
debugger team to play with would be nice, and I will certainly try to
spend some time on reviews.

FTR, next thing on the Sony list will be the new range-list/loc-list
format.  We're really hoping to make `-gdwarf-5` a viable thing for
debuggers to try out by LLVM 7.0.  It won't have "everything" but the
basic set of sections should be in place and be syntactically correct.


> regards,
> Pavel

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