On irc, Iain Buclaw pointed out that the new DWARF indexer broke "start" for D. This is easily fixed, but more testing showed that it also broke Rust. It's not entirely trivial to fix. The issue is that in dwarf2_build_psymtabs_hard: const cooked_index_entry *main_entry = vec->get_main (); if (main_entry != nullptr) set_objfile_main_name (objfile, main_entry->name, main_entry->per_cu->lang ()); ... here we'd like to use the entry's full name. But, the entry hasn't been canonicalized yet, so doing this would actually crash. Note though that Rust doesn't require canonicalization. And, the languages that do require canonicalization don't need this mechanism for finding "main". So, I think at least for now we could have a hack to handle this. Longer term, perhaps resurrecting an old patch of mine to make "main"-finding more lazy (lookup on first use) would be good. This way the index could be "clean" and wait for the finalization to be done, while not pausing the UI in the normal case... the problem with the current code being that for "gdb exe", gdb eagerly wants to set the current language, but really this could be done on demand.
I have a patch for this, but haven't written a 'start' test for D yet.
The master branch has been updated by Tom Tromey <tromey@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=47fe57c92810c7302bb80eafdec6f4345bcc69c8 commit 47fe57c92810c7302bb80eafdec6f4345bcc69c8 Author: Tom Tromey <tom@tromey.com> Date: Mon Feb 13 17:44:54 2023 -0700 Fix "start" for D, Rust, etc The new DWARF indexer broke "start" for some languages. For D, it is broken because, while the code in cooked_index_shard::add specifically excludes Ada, it fails to exclude D. This means that the C "main" will be detected as "main" here -- whereas what is intended is for the code in find_main_name to use d_main_name to find the name. The Rust compiler, on the other hand, uses DW_AT_main_subprogram. However, the code in dwarf2_build_psymtabs_hard fails to create a fully-qualified name, so the name always ends up as plain "main". For D and Ada, a very simple approach suffices: remove the check against "main" from cooked_index_shard::add. This also has the benefit of slightly speeding up DWARF indexing. I assume this approach will work for Pascal and Modula-2 as well, but I don't have a way to test those at present. For Rust, though, this is not sufficient. And, computing the fully-qualified name in dwarf2_build_psymtabs_hard will crash, because cooked_index_entry::full_name uses the canonical name -- and that is not computed until after canonicalization. However, we don't want to wait for canonicalization to be done before computing the main name. That would remove any benefit from doing canonicalization is the background. This patch solves this dilemma by noticing that languages using DW_AT_main_subprogram are, currently, disjoint from languages requiring canonicalization. Because of this, we can add a parameter to full_name to let us avoid crashes, slowdowns, and races here. This is kind of tricky and ugly, so I've tried to comment it sufficiently. While doing this, I had to change gdb.dwarf2/main-subprogram.exp. A different possibility here would be to ignore the canonicalization needs of C in this situation, because those only affect certain types. However, I chose this approach because the test case is artificial anyhow. A long time ago, in an earlier threading attempt, I changed the global current_language to be a function (hidden behind a macro) to let us attempt lazily computing the current language. Perhaps this approach could still be made to work. However, that also seemed rather tricky, more so than this patch. Reviewed-By: Andrew Burgess <aburgess@redhat.com> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30116
The gdb-13-branch branch has been updated by Tom Tromey <tromey@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=7f4307436fdab42da2b385040b90294f301ea55b commit 7f4307436fdab42da2b385040b90294f301ea55b Author: Tom Tromey <tom@tromey.com> Date: Mon Feb 13 17:44:54 2023 -0700 Fix "start" for D, Rust, etc The new DWARF indexer broke "start" for some languages. For D, it is broken because, while the code in cooked_index_shard::add specifically excludes Ada, it fails to exclude D. This means that the C "main" will be detected as "main" here -- whereas what is intended is for the code in find_main_name to use d_main_name to find the name. The Rust compiler, on the other hand, uses DW_AT_main_subprogram. However, the code in dwarf2_build_psymtabs_hard fails to create a fully-qualified name, so the name always ends up as plain "main". For D and Ada, a very simple approach suffices: remove the check against "main" from cooked_index_shard::add. This also has the benefit of slightly speeding up DWARF indexing. I assume this approach will work for Pascal and Modula-2 as well, but I don't have a way to test those at present. For Rust, though, this is not sufficient. And, computing the fully-qualified name in dwarf2_build_psymtabs_hard will crash, because cooked_index_entry::full_name uses the canonical name -- and that is not computed until after canonicalization. However, we don't want to wait for canonicalization to be done before computing the main name. That would remove any benefit from doing canonicalization is the background. This patch solves this dilemma by noticing that languages using DW_AT_main_subprogram are, currently, disjoint from languages requiring canonicalization. Because of this, we can add a parameter to full_name to let us avoid crashes, slowdowns, and races here. This is kind of tricky and ugly, so I've tried to comment it sufficiently. While doing this, I had to change gdb.dwarf2/main-subprogram.exp. A different possibility here would be to ignore the canonicalization needs of C in this situation, because those only affect certain types. However, I chose this approach because the test case is artificial anyhow. A long time ago, in an earlier threading attempt, I changed the global current_language to be a function (hidden behind a macro) to let us attempt lazily computing the current language. Perhaps this approach could still be made to work. However, that also seemed rather tricky, more so than this patch. Reviewed-By: Andrew Burgess <aburgess@redhat.com> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30116 (cherry picked from commit 47fe57c92810c7302bb80eafdec6f4345bcc69c8)
Fixed.