[Lldb-commits] [PATCH] D84402: [lldb/DWARF] Add more line table validation

[Greg Clayton via Phabricator via lldb-commits]

clayborg added inline comments.


================
Comment at: lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp:1044
   for (const llvm::DWARFDebugLine::Sequence &seq : line_table->Sequences) {
+    if (!list.ContainsFileAddressRange(seq.LowPC, seq.HighPC - seq.LowPC))
+      continue;
----------------
dblaikie wrote:
> Could you specifically look for/propagate tombstones here, to reduce the risk of large functions overlapping with the valid address range, even when they're tombstoned to zero? (because zero+large function size could still end up overlapping with valid code)
> 
> To do that well, I guess it'd have to be implemented at a lower-layer, inside the line table state machine - essentially dropping all lines derived from a "set address" operation that specifies a tombstone.
Just checking if the section lists contains an address doesn't help weed out addresses that were tombstoned to zero since our PT_LOAD[0] will almost always contain zero for shared libraries. It might be nice to make a list of addresses that come from sections with read + execute permissions and store that in SymbolFileDWARF one time at startup. Then these searches will be faster as we are looking in less ranges, and most likely will not contain address zero. This code will catch the -1 and -2 tombstones, but most linkers I have run into use zero and the tombstone. 

If our algorithm only checks sections with no subsections and then makes a list of file addresses for and section ranges for those, we should have a great list. The entire PT_LOAD[0] will usually be mapped read + execute, so we can't just check top level sections for ELF. Mach-o also has this issue __TEXT in mac is also mapped read + execute and usually contains zero for shared libraries, but since the sections must come after the mach-o header, the sections within the __TEXT segment have correct permissions and would work, just like they would for ELF.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D84402/new/

https://reviews.llvm.org/D84402