Re: [PATCH v3 2/3] gdb: Make the parser recognize the [[N]] syntax for variables

[Eli Zaretskii <eliz@gnu.org>]

> From: Guinevere Larsen <guinevere@redhat.com>
> Cc: Guinevere Larsen <guinevere@redhat.com>
> Date: Thu, 19 Jun 2025 15:05:39 -0300
> 
> This commit adds a couple new rules to the YACC parser, that will allow
> GDB to recognize expressions like [[N]]::var.
> 
> This new syntax re-uses the existing rules for searching for "block"s,
> because it allows, with minimal changes to the .y file as a whole, while
> also allowing [[N]]::function::symbol work. Notably, [[N]]::'file.c'::var
> does not work yet, as this code change is also involved and would pollute
> the current commit, so will be done in a separate one in the same series.
> 
> To restrict the search to a desired namespace, a new function is
> introduced,  lookup_symbol_in_linker_namespace.  This function will only
> perform the symbol lookup in the objfiles that belong to the requested
> namespace.
> 
> This commit also changes the error message when "print var" if "var" is
> only present in namespaces other than the current one. Before this commit,
> lookup_minimal_symbol would find them as "external" symbols with
> incomplete information - outputting "<symbol> has incomplete
> information, cast it to it's defined type." - which could be confusing for
> the users. This commit changes the parser rule "variable: name_not_typename"
> so that, if multiple namespaces are active, we'll look for minimal symbols
> only in the current namespace.
> 
> Known limitations:
> * When using [[N]]::foo::var, if that specific foo version is not on the
>   stack, the error will be unable to include the linker namespace
>   requested.  So if a user sees "foo" in the stack this could be
>   confusing, but it should be mitigated when a future patch adds the
>   namespace ID to the backtrace where applicable.
> * Completion is not supported.  That's because the function used to
>   complete symbols expects only text in the form "file.c:symbol", so
>   can't handle the double colon.  This isn't unique to linker
>   namespaces, though, since func::var will also not complete, it is just
>   a quirk of how :: completion work at this point.
> * The expression that parses [[N]] only takes an integer.  That's
>   because there aren't many expressions that would make sense in there,
>   and the work of accepting an arbitrary expression felt too much for
>   little gain.
> ---
>  gdb/NEWS                                     |   6 +
>  gdb/c-exp.y                                  |  72 ++++++++---
>  gdb/doc/gdb.texinfo                          |   6 +
>  gdb/minsyms.c                                | 124 ++++++++++++-------
>  gdb/minsyms.h                                |   8 ++
>  gdb/parser-defs.h                            |   7 ++
>  gdb/symtab.c                                 |  37 ++++++
>  gdb/symtab.h                                 |   8 ++
>  gdb/testsuite/gdb.base/dlmopen-ns-ids-lib.c  |  14 +++
>  gdb/testsuite/gdb.base/dlmopen-ns-ids-main.c |   3 +
>  gdb/testsuite/gdb.base/dlmopen-ns-ids.exp    |  47 +++++++
>  11 files changed, 268 insertions(+), 64 deletions(-)

Thanks.

> --- a/gdb/NEWS
> +++ b/gdb/NEWS
> @@ -102,6 +102,12 @@ info threads [-gid] [-stopped] [-running] [ID]...
>    These new flags can be useful to get a reduced list when there is a
>    large number of threads.
>  
> +print
> +  The print command now accepts the following syntax to print values
> +  from a specific linker namespace: `[[N]]::foo'.  N is the namespace
> +  identifier as understood by GDB.

This part is okay.

> --- a/gdb/doc/gdb.texinfo
> +++ b/gdb/doc/gdb.texinfo
> @@ -10565,6 +10565,12 @@ you can choose a different format by specifying @samp{/@var{f}}, where
>  @var{f} is a letter specifying the format; see @ref{Output Formats,,Output
>  Formats}.
>  
> +Additionally, if the inferior supports linker namespaces, @value{GDBN}
> +has implemented the following syntax to allow users to resolve symbols
> +to a specific namespace: @code{[[@var{n}]]::@var{symbol}}.  Here @var{n}
> +is @value{GDBN}'s namespace identifier, which may be different to the
> +inferior's identifier.

This part is also okay, but please say "different from" in the last
sentence.

Reviewed-By: Eli Zaretskii <eliz@gnu.org>