[PATCH] Debug support for global alias variable
Natarajan, Kavitha
Kavitha.Natarajan@amd.com
Fri Mar 4 13:44:38 GMT 2022
[AMD Official Use Only]
Hi,
For the below testcase, when compiled with clang compiler, debugger is not able to print alias variable type or value.
$ cat test.c
int oldname = 1;
extern int newname attribute((alias("oldname")));
int main ()
{ return 0; }
$ clang -g -O0 test.c
$ gdb a.out
(gdb) ptype oldname
type = int
(gdb) ptype newname
type = <data variable, no debug info>
(gdb) p oldname
$1 = 1
(gdb) p newname
'newname' has unknown type; cast it to its declared type
This is because clang is not emitting dwarf information for alias variable. I have updated clang patch (originally from https://reviews.llvm.org/D103131) to emit debug info for alias variable as imported entity (DW_TAG_imported_declaration):
https://reviews.llvm.org/D120989
However, gdb cannot handle the imported declaration for alias variables. GCC emits debug info for alias variables as DW_TAG_variable which gdb can handle. The discussions in the llvm bug report bug-50052<https://bugs.llvm.org/show_bug.cgi?id=50052> and above review links talk about why it is appropriate to emit alias variable as DW_TAG_imported_declaration rather than DW_TAG_variable. Refer section "3.2.3 Imported (or Renamed) Declaration Entries" in DWARF 5 specification. It was also previously discussed in gdb forum in the below thread:
https://sourceware.org/pipermail/gdb/2021-June/049509.html
The attached gdb patch can handle DW_TAG_imported_declaration as alias variables. This change fixes the failure in testcase:
gdb.base/symbol-alias.exp
This testcase is also updated to test nested (recursive) alias, static aliasee and deferred aliasee.
Please review the below gdb patch (also attached).
---
gdb/dwarf2/read.c | 113 ++++++++++++++++--------
gdb/testsuite/gdb.base/symbol-alias.exp | 23 ++++-
gdb/testsuite/gdb.base/symbol-alias2.c | 10 +++
3 files changed, 107 insertions(+), 39 deletions(-)
diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 10550336063..0f709d9ccc1 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 int read_alias (struct die_info *die, struct dwarf2_cu *cu);
static struct type *read_module_type (struct die_info *die,
struct dwarf2_cu *cu);
@@ -9742,9 +9746,11 @@ process_die (struct die_info *die, struct dwarf2_cu *cu)
break;
case DW_TAG_imported_declaration:
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 +10218,20 @@ 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
+
+/* Inspect DIE in CU for a namespace alias or a variable
+ with alias attribute. If one exists, record a new symbol
+ for it.
- Returns 1 if a namespace alias was recorded, 0 otherwise. */
+ Returns 1 if an alias was recorded, 0 otherwise. */
static int
-read_namespace_alias (struct die_info *die, struct dwarf2_cu *cu)
+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. */
+ /* The die must have a name for namespace or variable alias */
attr = dwarf2_attr (die, DW_AT_name, cu);
if (attr != NULL)
{
@@ -10232,42 +10240,71 @@ 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. */
for (num = 0; num < MAX_NESTED_IMPORTED_DECLARATIONS; ++num)
- {
- attr = dwarf2_attr (d, DW_AT_import, cu);
- if (attr == NULL)
- break;
+ {
+ attr = dwarf2_attr (d, DW_AT_import, cu);
+ if (attr == NULL)
+ return 0;
- d = follow_die_ref (d, attr, &imported_cu);
- if (d->tag != DW_TAG_imported_declaration)
- break;
- }
+ d = follow_die_ref (d, attr, &imported_cu);
+ if (d->tag != DW_TAG_imported_declaration)
+ break;
+ }
if (num == MAX_NESTED_IMPORTED_DECLARATIONS)
- {
- complaint (_("DIE at %s has too many recursively imported "
- "declarations"), sect_offset_str (d->sect_off));
- return 0;
- }
+ {
+ complaint (_("DIE at %s has too many recursively imported "
+ "declarations"), sect_offset_str (d->sect_off));
+ return 0;
+ }
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)
- {
- /* 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;
- }
- }
+ {
+ struct type *type;
+ if (d->tag == DW_TAG_variable)
+ {
+ /* 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);
+ if (attr != nullptr)
+ {
+ var_decode_location (attr, sym, cu);
+ return 1;
+ }
+ else
+ {
+ /* We do not know the address of this symbol.
+ If it is an external symbol and we have type information
+ for it, enter the symbol as a LOC_UNRESOLVED symbol.
+ The address of the variable will then be determined from
+ the minimal symbol table whenever the variable is
+ referenced. */
+ attr = dwarf2_attr (d, DW_AT_external, imported_cu);
+ if (attr != nullptr && attr->as_boolean ()
+ && dwarf2_attr (d, DW_AT_type, imported_cu) != NULL)
+ {
+ sym->set_aclass_index (LOC_UNRESOLVED);
+ return 1;
+ }
+ }
+ }
+ 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 1;
+ }
+ }
+ }
}
-
return 0;
}
diff --git a/gdb/testsuite/gdb.base/symbol-alias.exp b/gdb/testsuite/gdb.base/symbol-alias.exp
index 2b53cc31053..1259c1daf1d 100644
--- a/gdb/testsuite/gdb.base/symbol-alias.exp
+++ b/gdb/testsuite/gdb.base/symbol-alias.exp
@@ -15,6 +15,7 @@
# 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*]
if { [prepare_for_testing "failed to prepare" ${testfile} [list $srcfile $srcfile2]] } {
return -1
@@ -31,6 +32,26 @@ foreach f {"func" "func_alias"} {
}
# Variables.
-foreach v {"g_var_s" "g_var_s_alias"} {
+foreach v {"g_var_s" "g_var_s_alias" "g_var_s_alias2"} {
gdb_test "p $v" "= {field1 = 1, field2 = 2}"
}
+
+# Static Variable.
+foreach v {"g_var" "g_var_alias"} {
+ gdb_test "p $v" " = 1"
+}
+
+# Deferred Variable.
+gdb_test "p g_def_var" " = 2"
+gdb_test_multiple "p g_def_var_alias" "p g_def_var_alias" {
+ -re " = 2.*$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"
+ }
+ }
+}
diff --git a/gdb/testsuite/gdb.base/symbol-alias2.c b/gdb/testsuite/gdb.base/symbol-alias2.c
index 34f4e121e25..79b3195caf5 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 +40,11 @@ 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;
--
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