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[gdb/symtab] Prefer var def over decl

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Consider the DWARF as generated by gcc with the tentative patch to fix gcc
PR91507 - "wrong debug for completed array with previous incomplete
declaration":
...
 <1><f4>: Abbrev Number: 2 (DW_TAG_array_type)
    <f5>   DW_AT_type        : <0xff>
    <f9>   DW_AT_sibling     : <0xff>
 <2><fd>: Abbrev Number: 3 (DW_TAG_subrange_type)
 <2><fe>: Abbrev Number: 0
 <1><ff>: Abbrev Number: 4 (DW_TAG_pointer_type)
    <100>   DW_AT_byte_size   : 8
    <101>   DW_AT_type        : <0x105>
 <1><105>: Abbrev Number: 5 (DW_TAG_base_type)
    <106>   DW_AT_byte_size   : 1
    <107>   DW_AT_encoding    : 6       (signed char)
    <108>   DW_AT_name        : (indirect string, offset: 0x19f): char
 <1><10c>: Abbrev Number: 6 (DW_TAG_variable)
    <10d>   DW_AT_name        : zzz
    <111>   DW_AT_decl_file   : 1
    <112>   DW_AT_decl_line   : 1
    <113>   DW_AT_decl_column : 14
    <114>   DW_AT_type        : <0xf4>
    <118>   DW_AT_external    : 1
    <118>   DW_AT_declaration : 1
 <1><118>: Abbrev Number: 2 (DW_TAG_array_type)
    <119>   DW_AT_type        : <0xff>
    <11d>   DW_AT_sibling     : <0x128>
 <1><12f>: Abbrev Number: 8 (DW_TAG_variable)
    <130>   DW_AT_specification: <0x10c>
    <134>   DW_AT_decl_line   : 2
    <135>   DW_AT_decl_column : 7
    <136>   DW_AT_type        : <0x118>
    <13a>   DW_AT_location    : 9 byte block: 3 30 10 60 0 0 0 0 0      (DW_OP_addr: 601030)
...

The DWARF will result in two entries in the symbol table, a decl with type
char *[] and a def with type char*[2].

When trying to print the value of zzz:
...
$ gdb a.spec.out -batch -ex "p zzz"
...
the decl (rather than the def) will be found in the symbol table, which is
missing the location information, and consequently we get:
...
$1 = 0x601030 <zzz>
...

[ There is a fallback mechanism that finds the address of the variable in the
minimal symbol table, but that's not used here, because the type of the decl
does not specify a size.  We could use the symbol size here to get the size
of the type, but that's currently not done: PR exp/24989.  Still, fixing that
PR would not fix the generic case, where minimal symbol info is not
available. ]

Fix this by preferring defs over decls when searching in the symbol table.

Build and reg-tested on x86_64-linux.

gdb/ChangeLog:

2019-12-06  Tom de Vries  <tdevries@suse.de>

	PR symtab/24971
	* block.c (best_symbol, better_symbol): New function.
	(block_lookup_symbol_primary, block_lookup_symbol): Prefer def over
	decl.

gdb/testsuite/ChangeLog:

2019-12-06  Tom de Vries  <tdevries@suse.de>

	* gdb.dwarf2/varval.exp: Add decl before def test.

Change-Id: Id92326cb8ef9903b121ef9e320658eb565d0f5a9
This commit is contained in:
Tom de Vries 2019-12-06 18:51:49 +01:00
parent e8dc9b5bfd
commit 93e55f0a03
4 changed files with 123 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
gdb/ChangeLog
View File

@ -1,3 +1,10 @@
2019-12-06 Tom de Vries <tdevries@suse.de>
PR symtab/24971
* block.c (best_symbol, better_symbol): New function.
(block_lookup_symbol_primary, block_lookup_symbol): Prefer def over
decl.
2019-12-06 Tankut Baris Aktemur <tankut.baris.aktemur@intel.com>
* gdbtypes.h: Define the REFERENCE_SEE_THROUGH_BADNESS value.

74
gdb/block.c
View File

@ -657,6 +657,43 @@ block_iter_match_next (const lookup_name_info &name,
return block_iter_match_step (iterator, name, 0);
}
/* Return true if symbol A is the best match possible for DOMAIN. */
static bool
best_symbol (struct symbol *a, const domain_enum domain)
{
return (SYMBOL_DOMAIN (a) == domain
&& SYMBOL_CLASS (a) != LOC_UNRESOLVED);
}
/* Return symbol B if it is a better match than symbol A for DOMAIN.
Otherwise return A. */
static struct symbol *
better_symbol (struct symbol *a, struct symbol *b, const domain_enum domain)
{
if (a == NULL)
return b;
if (b == NULL)
return a;
if (SYMBOL_DOMAIN (a) == domain
&& SYMBOL_DOMAIN (b) != domain)
return a;
if (SYMBOL_DOMAIN (b) == domain
&& SYMBOL_DOMAIN (a) != domain)
return b;
if (SYMBOL_CLASS (a) != LOC_UNRESOLVED
&& SYMBOL_CLASS (b) == LOC_UNRESOLVED)
return a;
if (SYMBOL_CLASS (b) != LOC_UNRESOLVED
&& SYMBOL_CLASS (a) == LOC_UNRESOLVED)
return b;
return a;
}
/* See block.h.
Note that if NAME is the demangled form of a C++ symbol, we will fail
@ -684,7 +721,9 @@ block_lookup_symbol (const struct block *block, const char *name,
ALL_BLOCK_SYMBOLS_WITH_NAME (block, lookup_name, iter, sym)
{
if (SYMBOL_DOMAIN (sym) == domain)
/* See comment related to PR gcc/debug/91507 in
block_lookup_symbol_primary. */
if (best_symbol (sym, domain))
return sym;
/* This is a bit of a hack, but symbol_matches_domain might ignore
STRUCT vs VAR domain symbols. So if a matching symbol is found,
@ -692,7 +731,7 @@ block_lookup_symbol (const struct block *block, const char *name,
exactly the same domain. PR 16253. */
if (symbol_matches_domain (SYMBOL_LANGUAGE (sym),
SYMBOL_DOMAIN (sym), domain))
other = sym;
other = better_symbol (other, sym, domain);
}
return other;
}
@ -746,7 +785,34 @@ block_lookup_symbol_primary (const struct block *block, const char *name,
sym != NULL;
sym = mdict_iter_match_next (lookup_name, &mdict_iter))
{
if (SYMBOL_DOMAIN (sym) == domain)
/* With the fix for PR gcc/debug/91507, we get for:
...
extern char *zzz[];
char *zzz[ ] = {
"abc",
"cde"
};
...
DWARF which will result in two entries in the symbol table, a decl
with type char *[] and a def with type char *[2].
If we return the decl here, we don't get the value of zzz:
...
$ gdb a.spec.out -batch -ex "p zzz"
$1 = 0x601030 <zzz>
...
because we're returning the symbol without location information, and
because the fallback that uses the address from the minimal symbols
doesn't work either because the type of the decl does not specify a
size.
To fix this, we prefer def over decl in best_symbol and
better_symbol.
In absence of the gcc fix, both def and decl have type char *[], so
the only option to make this work is improve the fallback to use the
size of the minimal symbol. Filed as PR exp/24989. */
if (best_symbol (sym, domain))
return sym;
/* This is a bit of a hack, but symbol_matches_domain might ignore
@ -755,7 +821,7 @@ block_lookup_symbol_primary (const struct block *block, const char *name,
exactly the same domain. PR 16253. */
if (symbol_matches_domain (SYMBOL_LANGUAGE (sym),
SYMBOL_DOMAIN (sym), domain))
other = sym;
other = better_symbol (other, sym, domain);
}
return other;

4
gdb/testsuite/ChangeLog
View File

@ -1,3 +1,7 @@
2019-12-06 Tom de Vries <tdevries@suse.de>
* gdb.dwarf2/varval.exp: Add decl before def test.
2019-12-06 Tankut Baris Aktemur <tankut.baris.aktemur@intel.com>
* gdb.cp/rvalue-ref-overload.exp: Minor cleanup.

48
gdb/testsuite/gdb.dwarf2/varval.exp
View File

@ -55,7 +55,8 @@ proc setup_exec { arg_bad } {
var_b_label var_c_label var_p_label var_bad_label \
varval_label var_s_label var_untyped_label \
var_a_abstract_label var_a_concrete_label \
varval2_label
varval2_label varval3_def_label varval3_decl_label \
int_array_label int_array_of_1_label
set int_size [get_sizeof "int" -1]
@ -171,6 +172,32 @@ proc setup_exec { arg_bad } {
{DW_AT_location {DW_OP_addr [gdb_target_symbol "var_b"]} SPECIAL_expr}
}
int_array_label: DW_TAG_array_type {
{DW_AT_type :${int_label}}
} {
DW_TAG_subrange_type {}
}
varval3_decl_label: DW_TAG_variable {
{DW_AT_name "varval3"}
{DW_AT_type :${int_array_label}}
{DW_AT_external 1 DW_FORM_flag}
{DW_AT_declaration 1 DW_FORM_flag}
}
int_array_of_1_label: DW_TAG_array_type {
{DW_AT_type :${int_label}}
} {
DW_TAG_subrange_type {
{DW_AT_type :$int_label}
{DW_AT_upper_bound 0 DW_FORM_data1}
}
}
varval3_def_label: DW_TAG_variable {
{DW_AT_name "varval3"}
{DW_AT_external 1 DW_FORM_flag}
{DW_AT_type :${int_array_of_1_label}}
{DW_AT_location {DW_OP_addr [gdb_target_symbol "var_a"]} SPECIAL_expr}
}
DW_TAG_subprogram {
{MACRO_AT_func { "main" "${srcdir}/${subdir}/${srcfile}" }}
{DW_AT_type :${int_label}}
@ -277,19 +304,24 @@ proc setup_exec { arg_bad } {
if [prepare_for_testing "failed to prepare" ${executable} [list ${asm_file} ${srcfile}] {}] {
return -1
}
# DW_OP_GNU_variable_value implementation requires a valid frame.
if ![runto_main] {
return -1
}
}
if { [setup_exec 0] == -1 } {
return -1
}
with_test_prefix "pre-main" {
gdb_test "print varval3" "= \\{8\\}" ""
}
# DW_OP_GNU_variable_value implementation requires a valid frame.
if ![runto_main] {
return -1
}
gdb_test "print varval" "= 8"
gdb_test "print varval2" "= 8"
gdb_test "print varval3" "= \\{8\\}"
gdb_test "print constval" "= 53"
gdb_test "print mixedval" "= 42"
gdb_test "print pointerval" "= \\(int \\*\\) $hex <var_b>"
@ -311,6 +343,10 @@ if { [setup_exec 1] == -1 } {
return -1
}
# DW_OP_GNU_variable_value implementation requires a valid frame.
if ![runto_main] {
return -1
}
gdb_test "print badval" "value has been optimized out"
gdb_test "print bad_die_val1" \
"invalid dwarf2 offset 0xabcdef11"