[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 = (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 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; --