[lldb-dev] The mysterious case of unsupported DW_FORMs

[via lldb-dev]

I posted this suggestion on dwarf-discuss, where I would hope various tool maintainers are watching.

The maintainer of dwarfdump says that a new version now "prints the type of compression and the compression factor for each compressed section that's being reported."  Very small sections (< 100 bytes) tend to get larger, but he says he's seeing nearly 10x compression factors on string sections.  Other sections are in between these extremes.

Don't know about the GNU tools (readelf, objdump).

Did you file a bug for llvm-dwarfdump?  I haven't noticed one.
--paulr

From: Leonard Mosescu [mailto:mosescu at google.com]
Sent: Thursday, August 02, 2018 12:53 PM
To: Robinson, Paul
Cc: LLDB
Subject: Re: [lldb-dev] The mysterious case of unsupported DW_FORMs

Thanks Paul! I have a fix for the LLDB handling of compressed sections in an upcoming change (together with improved logging). The email was mostly in case some other poor soul hit the same problem (until I get a chance to commit the fixes)

(*) none of the tools bothered to make a note that the sections are compressed (SHF_COMPRESSED)
That seems like a completely valid feature request.  Again filing a bug would be the right tactic.  I'm willing to do this one for you, if you don't have a bugzilla account.

I'll open a request for llvm-dwarfdump. If you happen to be in touch with the developers of the other tools (readelf, objdump, dwarfdump) feel free to forward them the notes.



On Thu, Aug 2, 2018 at 7:21 AM, <paul.robinson at sony.com<mailto:paul.robinson at sony.com>> wrote:
Why weren't my local LLVM & LLDB builds able to decompress the sections? CMake!

Remembering to delete CMakeCache.txt is usually the part I forget to do.

LLDB tried to decompress, but when failed to do so it carried on returning and alter attempting to parse the compressed bytes as is.

A section that is compressed but can't be decompressed should be treated as corrupt/unparseable.  That seems like an LLDB bug; do you have an account on the project bugzilla?

(*) none of the tools bothered to make a note that the sections are compressed (SHF_COMPRESSED)

That seems like a completely valid feature request.  Again filing a bug would be the right tactic.  I'm willing to do this one for you, if you don't have a bugzilla account.

Thanks,
--paulr


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