Re: [PATCH] Debug support for global alias variable

[Bruno Larsen <blarsen@redhat.com>]

On 3/30/22 09:25, Natarajan, Kavitha wrote:
> [AMD Official Use Only]
> 
> Sorry, I missed to send the new patch. Please find it below:

Sorry for the delay on the response.

I only noticed one small nit in a comment. Like I said before, can't approve for pushing, but it LGTM.

> 
> ---------------------------------------------------------------------
> When clang emits the dwarf information of global alias variable
> as DW_TAG_imported_declaration, gdb does not handle it. GDB reads
> this tag as C++/fortran imported declaration (type alias, namespace
> alias and fortran module). Added support to handle this tag as
> alias variable.
> 
> This change fixes the failure in gdb.base/symbol-alias.exp testcase.
> This testcase is also updated to test nested (recursive) alias.
> ---
>   gdb/dwarf2/read.c                       | 75 +++++++++++++++++--------
>   gdb/testsuite/gdb.base/symbol-alias.exp | 63 ++++++++++++++++++++-
>   gdb/testsuite/gdb.base/symbol-alias2.c  | 16 ++++++
>   3 files changed, 128 insertions(+), 26 deletions(-)
> 
> diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
> index f9c942d91d3..12d66378f79 100644
> --- a/gdb/dwarf2/read.c
> +++ b/gdb/dwarf2/read.c
> @@ -1132,6 +1132,10 @@ static void add_partial_subprogram (struct partial_die_info *pdi,
>                                      CORE_ADDR *lowpc, CORE_ADDR *highpc,
>                                      int need_pc, struct dwarf2_cu *cu);
> 
> +static void var_decode_location (struct attribute *attr,
> +                                struct symbol *sym,
> +                                struct dwarf2_cu *cu);
> +
>   static unsigned int peek_abbrev_code (bfd *, const gdb_byte *);
> 
>   static struct partial_die_info *load_partial_dies
> @@ -1332,7 +1336,7 @@ static struct using_direct **using_directives (struct dwarf2_cu *cu);
> 
>   static void read_import_statement (struct die_info *die, struct dwarf2_cu *);
> 
> -static int read_namespace_alias (struct die_info *die, struct dwarf2_cu *cu);
> +static bool read_alias (struct die_info *die, struct dwarf2_cu *cu);
> 
>   static struct type *read_module_type (struct die_info *die,
>                                        struct dwarf2_cu *cu);
> @@ -9741,10 +9745,14 @@ process_die (struct die_info *die, struct dwarf2_cu *cu)
>         read_module (die, cu);
>         break;
>       case DW_TAG_imported_declaration:
> +      /* If the imported declaration is for global variable alias,
> +         this flag is set to false in read_alias function.  */
>         cu->processing_has_namespace_info = true;
> -      if (read_namespace_alias (die, cu))
> +      if (((cu->per_cu->lang == language_c)
> +          || (cu->per_cu->lang == language_cplus))
> +         && read_alias (die, cu))
>          break;
> -      /* The declaration is not a global namespace alias.  */
> +      /* The declaration is not a global namespace or variable alias.  */
>         /* Fall through.  */
>       case DW_TAG_imported_module:
>         cu->processing_has_namespace_info = true;
> @@ -10212,18 +10220,21 @@ dwarf2_physname (const char *name, struct die_info *die, struct dwarf2_cu *cu)
>     return retval;
>   }
> 
> -/* Inspect DIE in CU for a namespace alias.  If one exists, record
> -   a new symbol for it.
> +#define MAX_NESTED_IMPORTED_DECLARATIONS 100
> 
> -   Returns 1 if a namespace alias was recorded, 0 otherwise.  */
> +/* Inspect DIE in CU for a namespace alias or a variable
> +   with alias attribute. If one exists, record a new symbol
> +   for it.
> 
> -static int
> -read_namespace_alias (struct die_info *die, struct dwarf2_cu *cu)
> +   Returns "true" if an alias was recorded, "false" otherwise.  */
> +
> +static bool
> +read_alias (struct die_info *die, struct dwarf2_cu *cu)
>   {
>     struct attribute *attr;
> 
> -  /* If the die does not have a name, this is not a namespace
> -     alias.  */
> +  /* If the die does not have a name, this is not a namespace alias
> +     or variable alias.  */
>     attr = dwarf2_attr (die, DW_AT_name, cu);
>     if (attr != NULL)
>       {
> @@ -10232,13 +10243,12 @@ read_namespace_alias (struct die_info *die, struct dwarf2_cu *cu)
>         struct dwarf2_cu *imported_cu = cu;
> 
>         /* If the compiler has nested DW_AT_imported_declaration DIEs,
> -        keep inspecting DIEs until we hit the underlying import.  */
> -#define MAX_NESTED_IMPORTED_DECLARATIONS 100
> +         keep inspecting DIEs until we hit the underlying import.  */

This comment still has 8 spaces instead of a tab. You must have missed it on your pass.

>         for (num = 0; num  < MAX_NESTED_IMPORTED_DECLARATIONS; ++num)
>          {
>            attr = dwarf2_attr (d, DW_AT_import, cu);
>            if (attr == NULL)
> -           break;
> +           return false;
> 
>            d = follow_die_ref (d, attr, &imported_cu);
>            if (d->tag != DW_TAG_imported_declaration)
> @@ -10249,26 +10259,43 @@ read_namespace_alias (struct die_info *die, struct dwarf2_cu *cu)
>          {
>            complaint (_("DIE at %s has too many recursively imported "
>                         "declarations"), sect_offset_str (d->sect_off));
> -         return 0;
> +         return false;
>          }
> 
>         if (attr != NULL)
>          {
>            struct type *type;
> -         sect_offset sect_off = attr->get_ref_die_offset ();
> -
> -         type = get_die_type_at_offset (sect_off, cu->per_cu, cu->per_objfile);
> -         if (type != NULL && type->code () == TYPE_CODE_NAMESPACE)
> +         if (d->tag == DW_TAG_variable)
>              {
> -             /* This declaration is a global namespace alias.  Add
> -                a symbol for it whose type is the aliased namespace.  */
> -             new_symbol (die, type, cu);
> -             return 1;
> +             /* This declaration is a global variable alias. Add
> +                a symbol for it whose type is same as aliased variable.  */
> +             type = die_type (d, imported_cu);
> +             struct symbol *sym = new_symbol (die, type, cu);
> +             attr = dwarf2_attr (d, DW_AT_location, imported_cu);
> +             sym->set_aclass_index (LOC_UNRESOLVED);
> +             if (attr != nullptr)
> +               {
> +                 var_decode_location (attr, sym, cu);
> +               }
> +             /* Reset the flag as it is not a namespace alias.  */
> +             cu->processing_has_namespace_info = false;
> +             return true;
> +           }
> +         else
> +           {
> +             sect_offset sect_off = attr->get_ref_die_offset ();
> +             type = get_die_type_at_offset (sect_off, cu->per_cu, cu->per_objfile);
> +             if (type != NULL && type->code () == TYPE_CODE_NAMESPACE)
> +               {
> +                 /* This declaration is a global namespace alias. Add
> +                    a symbol for it whose type is the aliased namespace.  */
> +                 new_symbol (die, type, cu);
> +                 return true;
> +               }
>              }
>          }
>       }
> -
> -  return 0;
> +  return false;
>   }
> 
>   /* Return the using directives repository (global or local?) to use in the
> diff --git a/gdb/testsuite/gdb.base/symbol-alias.exp b/gdb/testsuite/gdb.base/symbol-alias.exp
> index 2b53cc31053..a9487b25f4d 100644
> --- a/gdb/testsuite/gdb.base/symbol-alias.exp
> +++ b/gdb/testsuite/gdb.base/symbol-alias.exp
> @@ -15,6 +15,9 @@
>   # along with this program.  If not, see <http://www.gnu.org/licenses/>.
> 
>   standard_testfile symbol-alias.c symbol-alias2.c
> +set using_clang [test_compiler_info clang-*]
> +set old_clang [expr [test_compiler_info {clang-1[0-3]-*-*}] \
> +                || [test_compiler_info {clang-[1-9]-*}]]
> 
>   if { [prepare_for_testing "failed to prepare" ${testfile} [list $srcfile $srcfile2]] } {
>       return -1
> @@ -31,6 +34,62 @@ foreach f {"func" "func_alias"} {
>   }
> 
>   # Variables.
> -foreach v {"g_var_s" "g_var_s_alias"} {
> -    gdb_test "p $v" "= {field1 = 1, field2 = 2}"
> +gdb_test "p g_var_s" "= {field1 = 1, field2 = 2}"
> +foreach v {"g_var_s_alias" "g_var_s_alias2"} {
> +    gdb_test_multiple "p $v" "p $v" {
> +       -re  " = {field1 = 1, field2 = 2}.*$gdb_prompt $" {
> +           pass "print alias of variable $v"
> +       }
> +       -re  ".*has unknown type; cast it to its declared type.*$gdb_prompt $" {
> +           if { $old_clang } {
> +               xfail "print alias variable $v"
> +           } else {
> +               fail "print alias variable $v"
> +           }
> +       }
> +    }
> +}
> +
> +# Static Variable.
> +gdb_test "p g_var" " = 1"
> +gdb_test_multiple "p g_var_alias" "p g_var_alias" {
> +    -re  " = 1.*$gdb_prompt $" {
> +       pass "print alias of static variable"
> +    }
> +    -re  ".*has unknown type; cast it to its declared type.*$gdb_prompt $" {
> +       if { $old_clang } {
> +         xfail "print alias of static variable"
> +       } else {
> +         fail "print alias of static variable"
> +       }
> +    }
> +}
> +
> +# Deferred Variable.
> +gdb_test "p g_def_var" " = 2"
> +gdb_test_multiple "p g_def_var_alias" "p g_def_var_alias" {
> +    -re  " = 2.*$gdb_prompt $" {
> +       pass "print alias of deferred variable"
> +    }
> +    -re  ".*has unknown type; cast it to its declared type.*$gdb_prompt $" {
> +       if { $using_clang } {
> +         xfail "print alias of deferred variable"
> +       } else {
> +         fail "print alias of deferred variable"
> +       }
> +    }
> +}
> +
> +# Alias of deferred Variable alias.
> +gdb_test_multiple "p g_def_var2_alias2" "p g_def_var2_alias2" {
> +    -re  " = 3.*$gdb_prompt $" {
> +       pass "print alias of alias of deferred variable"
> +    }
> +    -re  ".*has unknown type; cast it to its declared type.*$gdb_prompt $" {
> +       if { $old_clang } {
> +         xfail "print alias of alias of deferred variable"
> +       } else {
> +         fail "print alias of alias of deferred variable"
> +       }
> +    }
>   }
> diff --git a/gdb/testsuite/gdb.base/symbol-alias2.c b/gdb/testsuite/gdb.base/symbol-alias2.c
> index 34f4e121e25..41d4b6a53e5 100644
> --- a/gdb/testsuite/gdb.base/symbol-alias2.c
> +++ b/gdb/testsuite/gdb.base/symbol-alias2.c
> @@ -23,6 +23,8 @@ struct S
> 
>   struct S g_var_s = { 1, 2 };
> 
> +static int g_var = 1;
> +
>   #ifdef __cplusplus
>   /* So that the alias attribute below work without having to figure out
>      this function's mangled name.  */
> @@ -38,3 +40,17 @@ func (void)
>   struct S *func_alias (void) __attribute__ ((alias ("func")));
> 
>   extern struct S g_var_s_alias __attribute__ ((alias ("g_var_s")));
> +
> +extern struct S g_var_s_alias2 __attribute__ ((alias ("g_var_s_alias")));
> +
> +extern int g_var_alias __attribute__ ((alias ("g_var")));
> +
> +extern int g_def_var_alias __attribute__ ((alias ("g_def_var")));
> +
> +int g_def_var = 2;
> +
> +extern int g_def_var2_alias __attribute__ ((alias ("g_def_var2")));
> +
> +int g_def_var2 = 3;
> +
> +extern int g_def_var2_alias2 __attribute__ ((alias ("g_def_var2_alias")));
> --
> 
> Regards,
> Kavitha


-- 
Cheers!
Bruno Larsen