Re: [PATCH] Fix "set debug parser"

[Simon Marchi <simark@simark.ca>]

On 2025-04-26 19:12, Tom Tromey wrote:
> While debugging my longer series, I discovered that I broken "set
> debug parser" a couple years ago.  This patch fixes it and adds a
> minimal test case so that it, hopefully, will not break again.
> 
> This patch also adds parser debugging to the C++ name canonicalizer.

I think this introduced some tsan failures, since multiple threads write
yydebug without synchronization:

  WARNING: ThreadSanitizer: data race (pid=1311054)
    Read of size 4 at 0x58c55ad4a1f0 by thread T5:
      #0 scoped_restore_tmpl<int>::scoped_restore_tmpl<bool>(int*, bool) /home/simark/src/binutils-gdb/gdb/../gdbsupport/scoped_restore.h:71 (gdb+0xb7a0fe) (BuildId: 8f118bec5111347e0f2a78a7dc2fed594eb4ef55)
      #1 scoped_restore_tmpl<int> make_scoped_restore<int, bool>(int*, bool) /home/simark/src/binutils-gdb/gdb/../gdbsupport/scoped_restore.h:115 (gdb+0xb6bdbd) (BuildId: 8f118bec5111347e0f2a78a7dc2fed594eb4ef55)
      #2 cp_demangled_name_to_comp(char const*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >*) /home/simark/src/binutils-gdb/gdb/cp-name-parser.y:2051 (gdb+0xfaec69) (BuildId: 8f118bec5111347e0f2a78a7dc2fed594eb4ef55)
      #3 cp_canonicalize_string(char const*) /home/simark/src/binutils-gdb/gdb/cp-support.c:635 (gdb+0xfbf01d) (BuildId: 8f118bec5111347e0f2a78a7dc2fed594eb4ef55)
      #4 c_canonicalize_name(char const*) /home/simark/src/binutils-gdb/gdb/c-lang.c:732 (gdb+0xe70f6f) (BuildId: 8f118bec5111347e0f2a78a7dc2fed594eb4ef55)
      #5 cooked_index_shard::finalize(parent_map_map const*) /home/simark/src/binutils-gdb/gdb/dwarf2/cooked-index-shard.c:273 (gdb+0x104cbcf) (BuildId: 8f118bec5111347e0f2a78a7dc2fed594eb4ef55)

Changing yydebug to be an std::atomic would probably fix it, but it's
generated by bison, not sure this is an option.  We'll probably need to
do a custom scoped restore type for this.

Simon