[LLVMdev] Advice for setting debug locations

[David Blaikie]

On Wed, Aug 13, 2014 at 3:47 PM, Keno Fischer
<kfischer at college.harvard.edu> wrote:
> Sorry, I didn't have a small IR example and I was sure I was just
> doing something stupid. Thanks for the help, I'll try it out and
> report back. Maybe it would be good to add an assertion or something
> that tells people what's wrong in this case, since the generated DWARF
> seems to be invalid?

I'm still not sure exactly where things went wrong for you, so unsure
as to where to add the assertion - a small IR example would be helpful
for that. The suggestion to use the DW_TAG_lexical_block 3-field-form
was just based on your description of your goals, it sounded like that
was the tool you needed & weren't using yet.

>
> On Wed, Aug 13, 2014 at 5:53 PM, David Blaikie <dblaikie at gmail.com> wrote:
>> Use the second form of DW_TAG_lexical_block metadata (the one with 3
>> fields - http://llvm.org/docs/SourceLevelDebugging.html#block-descriptors
>> ) to describe file changes within a sequence of LLVM IR functions.
>>
>> A small example of IR would be easier to follow if you want help
>> debugging why your IR is causing problems.
>>
>> On Wed, Aug 13, 2014 at 2:25 PM, Keno Fischer
>> <kfischer at college.harvard.edu> wrote:
>>> Hello,
>>>
>>> I'm trying to fix a long standing issue we are having in Julia where
>>> when the file information switched, we weren't recording that
>>> correctly, so line information showed up in the wrong file. Basically
>>> we would always create a scope with the DISubprogram and the given
>>> line number. What I tried was to change the scope to be a DIFile
>>> instead so we'd get the correct file information. Unfortunately I had
>>> to revert this [1], because it crashes llvm's dwarf reader (which we
>>> use to get line information for backtraces when exceptions are thrown)
>>> with the following backtrace:
>>>
>>> isNULL at /Users/kfischer/Documents/julia-debug/deps/llvm-svn/lib/DebugInfo/DWARFDebugInfoEntry.h:52
>>> getAddressRanges at
>>> /Users/kfischer/Documents/julia-debug/deps/llvm-svn/lib/DebugInfo/DWARFDebugInfoEntry.cpp:242
>>> collectAddressRanges at
>>> /Users/kfischer/Documents/julia-debug/deps/llvm-svn/lib/DebugInfo/DWARFUnit.cpp:302
>>> generate at /Users/kfischer/Documents/julia-debug/deps/llvm-svn/lib/DebugInfo/DWARFDebugAranges.cpp:54
>>> getDebugAranges at
>>> /Users/kfischer/Documents/julia-debug/deps/llvm-svn/lib/DebugInfo/DWARFContext.cpp:270
>>> getCompileUnitForAddress at
>>> /Users/kfischer/Documents/julia-debug/deps/llvm-svn/lib/DebugInfo/DWARFContext.cpp:423
>>>
>>> Can somebody tell me what the correct way to achieve this is?
>>>
>>> [1] https://github.com/JuliaLang/julia/commit/e494cb6dff193ecb0e254981be0f1122ae294d04
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