Fix off-by-one error in DWARF reg-reg location (#317) #321
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The DWARF specification states that the form of an exprloc consists of an unsigned LEB128 length value, followed by the encoded location bytes of the specified length. For some reason we were adding one to the length value being emitted. This looks incorrect to me. The above calculation for REG-REG (a variable stored in two registers) correctly calculates the length of each register type tag, plus the size of the interpolating PIECE tags, plus the size of notation for each register. The extra byte looks wrong. I've tested this locally and it appears to resolve dotnet/runtime#77407. Unfortunately, it also causes llvm-dwarfdump --verify to constantly complain about missing base addresses. I can't confirm at the moment, but my suspicion is that this is revealing an existing bug. Even if this is somehow causing a new bug, I think the resulting symbols with this change are better than the alternative (no working symbols at all). (cherry picked from commit b85b64b)
jeffschwMSFT
approved these changes
Nov 17, 2022
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Backport of #317
Customer impact
Without this change, symbols are broken on Linux release builds such that no debugging is functional. Found in both manual testing and customer reported soon after shipping.
Testing
Manual testing. Verified using llvm-dwarfdump and gdb, and verified no Windows regression using Visual Studio.
Risk
Low. This is a focused change, and Windows has been scouted for regressions. It's probably not possible to make Linux worse than it already is.