[ was: Re: [PATCH][debug] Add -gforce-named-dies ]
On 08/22/2018 11:46 AM, Tom de Vries wrote:
> On 08/22/2018 08:56 AM, Tom de Vries wrote:
>> This is an undocumented developer-only option, because using this option may
>> change behaviour of dwarf consumers, f.i., gdb shows the artificial
>> variables:
>> ...
>> (gdb) info locals
>> a = 0x7fffffffda90 "\005"
>> D.4278 = <optimized out>
>> ...
> I just found in the dwarf 5 spec the attribute DW_AT_description
> (present since version 3):
> ...
> 2.20 Entity Descriptions
> Some debugging information entries may describe entities in the program
> that are artificial, or which otherwise have a “name” that is not a
> valid identifier in the programming language.
>
> This attribute provides a means for the producer to indicate the purpose
> or usage of the containing debugging infor
>
> Generally, any debugging information entry that has, or may have, a
> DW_AT_name attribute, may also have a DW_AT_description attribute whose
> value is a null-terminated string providing a description of the entity.
>
> It is expected that a debugger will display these descriptions as part
> of displaying other properties of an entity.
> ...
>
> AFAICT, gdb currently does not explicitly handle this attribute, which I
> think means it's ignored.
>
> It seems applicable to use DW_AT_description at least for the artificial
> decls.
>
> Perhaps even for all cases that are added by the patch?
>
I've chosen for this option. Using DW_AT_desciption instead of
DW_AT_name should minimize difference in gdb behaviour with and without
-gdescriptive-dies.
> I'll rewrite the patch.
OK for trunk?
Thanks,
- Tom
[debug] Add -gdescriptive-dies
This patch adds option -gdescriptive-dies. It sets the DW_AT_description
attribute of dies that do not get a DW_AT_name attribute, to make it easier to
figure out what the die is describing.
The option exports the names of artificial variables:
...
DIE 0: DW_TAG_variable (0x7fa934dd54b0)
+ DW_AT_description: "D.1922"
DW_AT_type: die -> 0 (0x7fa934dd0d70)
DW_AT_artificial: 1
...
which can be traced back to gimple dumps:
...
char a[0:D.1922] [value-expr: *a.0];
...
Furthermore, it adds names to external references:
...
DIE 0: DW_TAG_subprogram (0x7fa88b9650f0)
+DW_AT_description: "main"
DW_AT_abstract_origin: die -> label: vla_1.c.6719312a + 29 (0x7fa88b965140)
...
Bootstrapped and reg-tested on x86_64, in combination with a patch that
switches the option on by default.
2018-08-15 Tom de Vries <tdevr...@suse.de>
* common.opt (gdescriptive-dies): Add option.
* dwarf2out.c (add_name_and_src_coords_attributes): Add description
attribute for artifical and nameless decls.
(dwarf2out_register_external_die): Add description attribute to
external reference die.
(add_desc_attribute): New functions.
(gen_subprogram_die): Add description attribute to
DW_TAG_call_site_parameter.
* doc/invoke.texi (@item Debugging Options): Add -gdescriptive-dies and
-gno-descriptive-dies.
(@item -gdescriptive-dies): Add.
---
gcc/common.opt | 4 ++++
gcc/doc/invoke.texi | 6 +++++-
gcc/dwarf2out.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 67 insertions(+), 1 deletion(-)
diff --git a/gcc/common.opt b/gcc/common.opt
index ebc3ef43ce2..c2ba80c323f 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -2976,6 +2976,10 @@ gstrict-dwarf
Common Driver Report Var(dwarf_strict) Init(0)
Don't emit DWARF additions beyond selected version.
+gdescriptive-dies
+Common Driver Report Var(flag_descriptive_dies) Init(0)
+Add description attribute to DWARF DIEs that have no name attribute.
+
gtoggle
Common Driver Report Var(flag_gtoggle)
Toggle debug information generation.
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 99849ec6467..5a9c5b49481 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -372,7 +372,7 @@ Objective-C and Objective-C++ Dialects}.
-ginternal-reset-location-views -gno-internal-reset-location-views @gol
-ginline-points -gno-inline-points @gol
-gvms -gxcoff -gxcoff+ -gz@r{[}=@var{type}@r{]} @gol
--gsplit-dwarf @gol
+-gsplit-dwarf -gdescriptive-dies -gno-descriptive-dies @gol
-fdebug-prefix-map=@var{old}=@var{new} -fdebug-types-section @gol
-fno-eliminate-unused-debug-types @gol
-femit-struct-debug-baseonly -femit-struct-debug-reduced @gol
@@ -7395,6 +7395,10 @@ the build system to avoid linking files with debug information. To
be useful, this option requires a debugger capable of reading @file{.dwo}
files.
+@item -gdescriptive-dies
+@opindex gdescriptive-dies
+Add description attribute to DWARF DIEs that have no name attribute.
+
@item -gpubnames
@opindex gpubnames
Generate DWARF @code{.debug_pubnames} and @code{.debug_pubtypes} sections.
diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
index fb71ff349fa..e1d4ea50695 100644
--- a/gcc/dwarf2out.c
+++ b/gcc/dwarf2out.c
@@ -3808,6 +3808,7 @@ static bool add_location_or_const_value_attribute (dw_die_ref, tree, bool);
static bool tree_add_const_value_attribute (dw_die_ref, tree);
static bool tree_add_const_value_attribute_for_decl (dw_die_ref, tree);
static void add_name_attribute (dw_die_ref, const char *);
+static void add_desc_attribute (dw_die_ref, tree);
static void add_gnat_descriptive_type_attribute (dw_die_ref, tree, dw_die_ref);
static void add_comp_dir_attribute (dw_die_ref);
static void add_scalar_info (dw_die_ref, enum dwarf_attribute, tree, int,
@@ -6022,6 +6023,8 @@ dwarf2out_register_external_die (tree decl, const char *sym,
else
equate_decl_number_to_die (decl, die);
+ add_desc_attribute (die, decl);
+
/* Add a reference to the DIE providing early debug at $sym + off. */
add_AT_external_die_ref (die, DW_AT_abstract_origin, sym, off);
}
@@ -20529,6 +20532,53 @@ add_name_attribute (dw_die_ref die, const char *name_string)
}
}
+/* Generate a DW_AT_description attribute given some string value to be included
+ as the value of the attribute. */
+
+static void
+add_desc_attribute (dw_die_ref die, const char *name_string)
+{
+ if (!flag_descriptive_dies || dwarf_version < 3)
+ return;
+
+ if (name_string != NULL && *name_string != 0)
+ {
+ if (demangle_name_func)
+ name_string = (*demangle_name_func) (name_string);
+
+ add_AT_string (die, DW_AT_description, name_string);
+ }
+}
+
+/* Generate a DW_AT_description attribute given some decl to be included
+ as the value of the attribute. */
+
+static void
+add_desc_attribute (dw_die_ref die, tree decl)
+{
+ tree decl_name;
+
+ if (!flag_descriptive_dies || dwarf_version < 3)
+ return;
+
+ if (decl == NULL_TREE || !DECL_P (decl))
+ return;
+ decl_name = DECL_NAME (decl);
+
+ if (decl_name != NULL && IDENTIFIER_POINTER (decl_name) != NULL)
+ {
+ const char *name = dwarf2_name (decl, 0);
+ add_desc_attribute (die, name ? name : IDENTIFIER_POINTER (decl_name));
+ }
+ else if (TREE_CODE (decl) == VAR_DECL || TREE_CODE (decl) == CONST_DECL)
+ {
+ char buf[32];
+ char decl_letter = TREE_CODE (decl) == CONST_DECL ? 'C' : 'D';
+ sprintf (buf, "%c.%u", decl_letter, DECL_UID (decl));
+ add_desc_attribute (die, buf);
+ }
+}
+
/* Retrieve the descriptive type of TYPE, if any, make sure it has a
DIE and attach a DW_AT_GNAT_descriptive_type attribute to the DIE
of TYPE accordingly.
@@ -21287,12 +21337,17 @@ add_name_and_src_coords_attributes (dw_die_ref die, tree decl,
const char *name = dwarf2_name (decl, 0);
if (name)
add_name_attribute (die, name);
+ else
+ add_desc_attribute (die, decl);
+
if (! DECL_ARTIFICIAL (decl))
add_src_coords_attributes (die, decl);
if (!no_linkage_name)
add_linkage_name (die, decl);
}
+ else
+ add_desc_attribute (die, decl);
#ifdef VMS_DEBUGGING_INFO
/* Get the function's name, as described by its RTL. This may be different
@@ -23265,6 +23320,7 @@ gen_subprogram_die (tree decl, dw_die_ref context_die)
dw_die_ref die = NULL;
rtx tloc = NULL_RTX, tlocc = NULL_RTX;
rtx arg, next_arg;
+ tree arg_decl = NULL_TREE;
for (arg = (ca_loc->call_arg_loc_note != NULL_RTX
? XEXP (ca_loc->call_arg_loc_note, 0)
@@ -23329,6 +23385,7 @@ gen_subprogram_die (tree decl, dw_die_ref context_die)
tdie = lookup_decl_die (tdecl);
if (tdie == NULL)
continue;
+ arg_decl = tdecl;
}
else
continue;
@@ -23345,6 +23402,7 @@ gen_subprogram_die (tree decl, dw_die_ref context_die)
die = gen_call_site_die (decl, subr_die, ca_loc);
cdie = new_die (dwarf_TAG (DW_TAG_call_site_parameter), die,
NULL_TREE);
+ add_desc_attribute (cdie, arg_decl);
if (reg != NULL)
add_AT_loc (cdie, DW_AT_location, reg);
else if (tdie != NULL)
