SymbolFileBreakpad: Add line table support
This patch teaches SymbolFileBreakpad to parse the line information in
breakpad files and present it to lldb.
The trickiest question here was what kind of "compile units" to present
to lldb, as there really isn't enough information in breakpad files to
correctly reconstruct those.
A couple of options were considered
- have the entire file be one compile unit
- have one compile unit for each FILE record
- have one compile unit for each FUNC record
The main drawback of the first approach is that all of the files would
be considered "headers" by lldb, and so they wouldn't be searched if
target.inline-breakpoint-strategy=never. The single compile unit would
also be huge, and there isn't a good way to name it.
The second approach will create mostly correct compile units for cpp
files, but it will still be wrong for headers. However, the biggest
drawback here seemed to be the fact that this can cause a compile unit
to change mid-function (for example when a function from another file is
inlined or another file is #included into a function). While I don't
know of any specific thing that would break in this case, it does sound
like a thing that we should avoid.
In the end, we chose the third option, as it didn't seem to have any
major disadvantages, though it was not ideal either. One disadvantage
here is that this generates a large number of compile units, and there
is still a question on how to name it. We chose to simply name it after
the first line record in that function. This should be correct 99.99% of
the time, though it can produce somewhat strange results if the very
first line record comes from an #included file.
Reviewers: clayborg, zturner, lemo, markmentovai
Differential Revision: https://reviews.llvm.org/D56595