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Fix DWARF generation for enums #54004

Merged
merged 8 commits into from Oct 31, 2018
Merged

Fix DWARF generation for enums #54004

merged 8 commits into from Oct 31, 2018

Commits on Oct 30, 2018

  1. Fix DWARF generation for enums 

    The DWARF generated for Rust enums was always somewhat unusual.
Rather than using DWARF constructs directly, it would emit magic field
names like "RUST$ENCODED$ENUM$0$Name" and "RUST$ENUM$DISR".  Since
PR rust-lang#45225, though, even this has not worked -- the ad hoc scheme was
not updated to handle the wider variety of niche-filling layout
optimizations now available.

This patch changes the generated DWARF to use the standard tags meant
for this purpose; namely, DW_TAG_variant and DW_TAG_variant_part.

The patch to implement this went in to LLVM 7.  In order to work with
older versions of LLVM, and because LLVM doesn't do anything here for
PDB, the existing code is kept as a fallback mode.

Support for this DWARF is in the Rust lldb and in gdb 8.2.

Closes rust-lang#32920
Closes rust-lang#32924
Closes rust-lang#52762
Closes rust-lang#53153
    @tromey
    tromey committed Oct 30, 2018
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  2. Address review comments 

    This fixes the issues pointed out in review.
    @tromey
    tromey committed Oct 30, 2018
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  3. Tighten enum-debug test 

    Update the new enum-debug to ensure that field "D" does not have a
discrimnant.
    @tromey
    tromey committed Oct 30, 2018
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  4. Add more enum debug info tests 

    Rename the previous enum debug info test, and add more tests to cover
c-like enums and tagged (ordinary) enums.
    @tromey
    tromey committed Oct 30, 2018
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  5. Avoid possible integer overflow in niche value computation 

    @eddyb pointed out in review that the niche value computation had a
possible integer overflow problem, fixed here as he suggested.
    @tromey
    tromey committed Oct 30, 2018
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  6. Update enum debuginfo tests 

    Bug rust-lang#52452 notes some debuginfo test regressions when moving to gdb
8.1.  This series will also cause versions of gdb before 8.2 to fail
when a recent LLVM is used -- DW_TAG_variant_part support was not
added until 8.2.

This patch updates one of the builders to a later version of Ubuntu,
which comes with gdb 8.2.  It updates the relevant tests to require
both a new-enough LLVM and a new-enough gdb; the subsequent patch
arranges to continue testing the fallback mode.

The "gdbg" results are removed from these tests because the tests now
require a rust-enabled gdb.

If you read closely, you'll see that some of the lldb results in this
patch still look a bit strange.  This will be addressed in a
subsequent patch; I believe the fix is to disable the Python
pretty-printers when lldb is rust-enabled.
    @tromey
    tromey committed Oct 30, 2018
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  7. Add legacy debuginfo tests 

    The enum debuginfo patch includes a legacy mode that is used when
building against LLVM 5 and LLVM 6.  The main enum debuginfo tests
have been updated to rely on the new approach and a new-enough gdb.
This patch makes a copy of these tests so that the fallback mode will
continue to be tested.

Note that nil-enum.rs is not copied; it seemed not to provide enough
value to bother.

A new header directive is added, "ignore-llvm-version".  I will send a
patch to update the rustc documentation once this lands.
    @tromey
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  8. Update lldb 

    Update src/tools/lldb to pick up a needed bug fix in the
DW_TAG_variant_part handling.
    @tromey
    tromey committed Oct 30, 2018
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