Re: [PATCH v2 8/8] gdb/dwarf: read foreign type units

[Tom Tromey <tom@tromey.com>]

>>>>> "Simon" == Simon Marchi <simon.marchi@efficios.com> writes:

Simon> However, I know that the current GDB DWARF reader is not able to load
Simon> multiple type units with the same signature but different content.  Once
Simon> it loads one type unit with a given signature, all subsequent references
Simon> to that signature will use that loaded type unit.

FWIW this seems completely sensible to me, since the whole idea of
signatured types is to exploit ODR and linker features to reduce the
size of the DWARF.

Simon> Setting a dwarf2_per_cu's section a posteriori breaks the assumed
Simon> ordering of the dwarf2_per_bfd::all_units vector.  After setting the
Simon> section, re-sort the vector.

I'm not a huge fan of this but I guess we can live with it.

Simon> There is one known failure that I am unable to get to the bottom of.  It
Simon> seems orthogonal to my change though, more like an indexer or symbol
Simon> reader issue.  There are maybe more of this kind, but this is one
Simon> example:

Simon>   FAIL: gdb.ada/tick_length_array_enum_idx.exp: ptype variable_table'length (GDB internal error)
Simon>   /home/smarchi/src/binutils-gdb/gdb/dwarf2/read.c:1839: internal-error: search_one: Assertion `symtab != nullptr' failed.

See https://sourceware.org/bugzilla/show_bug.cgi?id=31648

Not really the same, but the same test case, so I kind of suspect that
older compilers had some issue here.  Though:

Simon> The issue seems sensitive to some aspects of the environment (gnat
Simon> version?).  I am able to reproduce the issue on Arch Linux (gnat 15)
Simon> with:

Simon>   $ make check TESTS="gdb.ada/tick_length_array_enum_idx.exp" RUNTESTFLAGS="--target_board=dwarf5-fission-debug-types-debug-names"

Simon> But it doesn't reproduce on Debian 13 (gnat 14), Ubuntu 24.04 (gnat
Simon> 13) or Fedora Rawhide (gnat 16).

... this goes against my thinking here.

One question is whether this compiler defaults to "minimal" encodings or
GNAT encodings.

Simon> +  /* A convenience function to allocate a signatured_type.  The
Simon> +     returned object has its "index" field set properly.
Simon> +

I don't really understand how the index field even really makes sense
any more, because now the vector is sorted after the fact.

Not that this is new with this change, just pointing out that it seems
incoherent with the description of the field:

  /* Our index in the unshared "symtabs" vector.  */

Like is this still true?

Approved-By: Tom Tromey <tom@tromey.com>

Tom