[PING][PATCH][gdb/ada] Handle artificial local symbols

[Tom de Vries <tdevries@suse.de>]

On 8/24/21 1:13 PM, Tom de Vries wrote:
> Hi,
> 
> With current master and gcc 7.5.0/8.5.0, we have this timeout:
> ...
> (gdb) print s^M
> Multiple matches for s^M
> [0] cancel^M
> [1] s at src/gdb/testsuite/gdb.ada/interface/foo.adb:20^M
> [2] s at src/gdb/testsuite/gdb.ada/interface/foo.adb:?^M
>> FAIL: gdb.ada/interface.exp: print s (timeout)
> ...
> 
> [ The FAIL doesn't reproduce with gcc 9.3.1.  This difference in
> behaviour bisects to gcc commit d70ba0c10de.
> 
> The FAIL with earlier gcc bisects to gdb commit ba8694b650b. ]
> 
> The FAIL is caused by gcc generating this debug info describing a named
> artificial variable:
> ...
>  <2><1204>: Abbrev Number: 31 (DW_TAG_variable)
>     <1205>   DW_AT_name        : s.14
>     <1209>   DW_AT_type        : <0x1213>
>     <120d>   DW_AT_artificial  : 1
>     <120d>   DW_AT_location    : 5 byte block: 91 e0 7d 23 18   \
>       (DW_OP_fbreg: -288; DW_OP_plus_uconst: 24)
> ...
> 
> An easy way to fix this would be to simply not put named artificial variables
> into the symbol table.  However, that causes regressions for Ada.  It relies
> on being able to get the value from such variables, using a named reference.
> 
> Fix this instead by marking the symbol as artificial, and:
> - ignoring such symbols in ada_resolve_variable, which fixes the FAIL
> - ignoring such ada symbols in do_print_variable_and_value, which prevents
>   them from showing up in "info locals"
> 
> Note that a fix for the latter was submitted here (
> https://sourceware.org/pipermail/gdb-patches/2008-January/054994.html ), and
> this patch borrows from it.
> 
> Tested on x86_64-linux.
> 
> Co-Authored-By: Joel Brobecker  <brobecker@adacore.com>
> 
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28180
> 
> Any comments?
> 

Ping.

Thanks,
- Tom

> [gdb/ada] Handle artificial local symbols
> 
> ---
>  gdb/ada-lang.c                      | 17 +++++++++++++++++
>  gdb/dwarf2/read.c                   |  5 +++++
>  gdb/language.h                      |  8 ++++++++
>  gdb/stack.c                         |  2 ++
>  gdb/symtab.h                        |  7 ++++++-
>  gdb/testsuite/gdb.ada/interface.exp |  7 +++++++
>  6 files changed, 45 insertions(+), 1 deletion(-)
> 
> diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
> index 6680a4fd657..487d92be5c9 100644
> --- a/gdb/ada-lang.c
> +++ b/gdb/ada-lang.c
> @@ -3539,6 +3539,17 @@ ada_resolve_variable (struct symbol *sym, const struct block *block,
>  	 candidates.end ());
>      }
>  
> +  /* Filter out artificial symbols.  */
> +  candidates.erase
> +    (std::remove_if
> +     (candidates.begin (),
> +      candidates.end (),
> +      [] (block_symbol &bsym)
> +      {
> +       return bsym.symbol->artificial;
> +      }),
> +     candidates.end ());
> +
>    int i;
>    if (candidates.empty ())
>      error (_("No definition found for %s"), sym->print_name ());
> @@ -13027,6 +13038,12 @@ class ada_language : public language_defn
>      return language_defn::read_var_value (var, var_block, frame);
>    }
>  
> +  /* See language.h.  */
> +  virtual bool symbol_printing_suppressed (struct symbol *symbol) const override
> +  {
> +    return symbol->artificial;
> +  }
> +
>    /* See language.h.  */
>    void language_arch_info (struct gdbarch *gdbarch,
>  			   struct language_arch_info *lai) const override
> diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
> index a8b44952dc0..9ff13abad40 100644
> --- a/gdb/dwarf2/read.c
> +++ b/gdb/dwarf2/read.c
> @@ -21644,6 +21644,11 @@ new_symbol (struct die_info *die, struct type *type, struct dwarf2_cu *cu,
>  	  sym->set_linkage_name (linkagename);
>  	}
>  
> +      /* Handle DW_AT_artificial.  */
> +      attr = dwarf2_attr (die, DW_AT_artificial, cu);
> +      if (attr != nullptr)
> +	sym->artificial = 1;
> +
>        /* Default assumptions.
>  	 Use the passed type or decode it from the die.  */
>        SYMBOL_DOMAIN (sym) = VAR_DOMAIN;
> diff --git a/gdb/language.h b/gdb/language.h
> index 21ed47b3580..40d22d20559 100644
> --- a/gdb/language.h
> +++ b/gdb/language.h
> @@ -327,6 +327,14 @@ struct language_defn
>      return {};
>    }
>  
> +  /* Return true if SYMBOL represents an entity that is not
> +     supposed to be seen by the user.  To be used to filter symbols
> +     during printing.  */
> +  virtual bool symbol_printing_suppressed (struct symbol *symbol) const
> +  {
> +    return false;
> +  }
> +
>    /* The per-architecture (OS/ABI) language information.  */
>  
>    virtual void language_arch_info (struct gdbarch *,
> diff --git a/gdb/stack.c b/gdb/stack.c
> index 516e4d45696..7c4cf9491cc 100644
> --- a/gdb/stack.c
> +++ b/gdb/stack.c
> @@ -2322,6 +2322,8 @@ do_print_variable_and_value (const char *print_name,
>    if (p->treg.has_value ()
>        && !treg_matches_sym_type_name (*p->treg, sym))
>      return;
> +  if (language_def (sym->language ())->symbol_printing_suppressed (sym))
> +    return;
>  
>    frame = frame_find_by_id (p->frame_id);
>    if (frame == NULL)
> diff --git a/gdb/symtab.h b/gdb/symtab.h
> index fd8dd62a406..fde083f22d5 100644
> --- a/gdb/symtab.h
> +++ b/gdb/symtab.h
> @@ -1122,7 +1122,8 @@ struct symbol : public general_symbol_info, public allocate_on_obstack
>        is_argument (0),
>        is_inlined (0),
>        maybe_copied (0),
> -      subclass (SYMBOL_NONE)
> +      subclass (SYMBOL_NONE),
> +      artificial (0)
>      {
>        /* We can't use an initializer list for members of a base class, and
>  	 general_symbol_info needs to stay a POD type.  */
> @@ -1192,6 +1193,10 @@ struct symbol : public general_symbol_info, public allocate_on_obstack
>  
>    ENUM_BITFIELD (symbol_subclass_kind) subclass : 2;
>  
> +  /* Whether this symbol is artificial.  */
> +
> +  unsigned int artificial : 1;
> +
>    /* Line number of this symbol's definition, except for inlined
>       functions.  For an inlined function (class LOC_BLOCK and
>       SYMBOL_INLINED set) this is the line number of the function's call
> diff --git a/gdb/testsuite/gdb.ada/interface.exp b/gdb/testsuite/gdb.ada/interface.exp
> index 68b51917e8d..2dfcd8e8afd 100644
> --- a/gdb/testsuite/gdb.ada/interface.exp
> +++ b/gdb/testsuite/gdb.ada/interface.exp
> @@ -33,3 +33,10 @@ gdb_test "print r" \
>  
>  gdb_test "print s" \
>           "= \\(x => 1, y => 2, w => 3, h => 4\\)"
> +
> +set cmd "info locals"
> +gdb_test $cmd \
> +    [multi_line \
> +	 $cmd \
> +	 "r = \[^\r\n\]*" \
> +	 "s = \[^\r\n\]*"]
>