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Print registers not saved in the frame as "<not saved>" instead of "<optimized out>".
Currently, in some scenarios, GDB prints <optimized out> when printing outer frame registers. An <optimized out> register is a confusing concept. What this really means is that the register is call-clobbered, or IOW, not saved by the callee. This patch makes GDB say that instead. Before patch: (gdb) p/x $rax $1 = <optimized out> (gdb) info registers rax rax <optimized out> After patch: (gdb) p/x $rax $1 = <not saved> (gdb) info registers rax rax <not saved> However, if for some reason the debug info describes a variable as being in such a register (**), we still want to print <optimized out> when printing the variable. IOW, <not saved> is reserved for inspecting registers at the machine level. The patch uses lval_register+optimized_out to encode the not saved registers, and makes it so that optimized out variables always end up in !lval_register values. ** See <https://sourceware.org/ml/gdb-patches/2012-08/msg00787.html>. Current/recent enough GCC doesn't mark variables/arguments as being in call-clobbered registers in the ranges corresponding to function calls, while older GCCs did. Newer GCCs will just not say where the variable is, so GDB will end up realizing the variable is optimized out. frame_unwind_got_optimized creates not_lval optimized out registers, so by default, in most cases, we'll see <optimized out>. value_of_register is the function eval.c uses for evaluating OP_REGISTER (again, $pc, etc.), and related bits. It isn't used for anything else. This function makes sure to return lval_register values. The patch makes "info registers" and the MI equivalent use it too. I think it just makes a lot of sense, as this makes it so that when printing machine registers ($pc, etc.), we go through a central function. We're likely to need a different encoding at some point, if/when we support partially saved registers. Even then, I think value_of_register will still be the spot to tag the intention to print machine register values differently. value_from_register however may also return optimized out lval_register values, so at a couple places where we're computing a variable's location from a dwarf expression, we convert the resulting value away from lval_register to a regular optimized out value. Tested on x86_64 Fedora 17 gdb/ 2013-10-02 Pedro Alves <palves@redhat.com> * cp-valprint.c (cp_print_value_fields): Adjust calls to val_print_optimized_out. * jv-valprint.c (java_print_value_fields): Likewise. * p-valprint.c (pascal_object_print_value_fields): Likewise. * dwarf2loc.c (dwarf2_evaluate_loc_desc_full) <DWARF_VALUE_REGISTER>: If the register was not saved, return a new optimized out value. * findvar.c (address_from_register): Likewise. * frame.c (put_frame_register): Tweak error string to say the register was not saved, rather than optimized out. * infcmd.c (default_print_one_register_info): Adjust call to val_print_optimized_out. Use value_of_register instead of get_frame_register_value. * mi/mi-main.c (output_register): Use value_of_register instead of get_frame_register_value. * valprint.c (valprint_check_validity): Likewise. (val_print_optimized_out): New value parameter. If the value is lval_register, print <not saved> instead. (value_check_printable, val_print_scalar_formatted): Adjust calls to val_print_optimized_out. * valprint.h (val_print_optimized_out): New value parameter. * value.c (struct value) <optimized_out>: Extend comment. (error_value_optimized_out): New function. (require_not_optimized_out): Use it. Use a different string for lval_register values. * value.h (error_value_optimized_out): New declaration. * NEWS: Mention <not saved>. gdb/testsuite/ 2013-10-02 Pedro Alves <palves@redhat.com> * gdb.dwarf2/dw2-reg-undefined.exp <pattern_rax_rbx_rcx_print, pattern_rax_rbx_rcx_info>: Set to "<not saved>". * gdb.mi/mi-reg-undefined.exp (opt_out_pattern): Delete. (not_saved_pattern): New. Replace use of the former with the latter. gdb/doc/ 2013-10-02 Pedro Alves <palves@redhat.com> * gdb.texinfo (Registers): Expand description of saved registers in frames. Explain <not saved>.
1 parent b477a5e commit 901461f

19 files changed

+154
-30
lines changed

‎gdb/ChangeLog

+30
Original file line numberDiff line numberDiff line change
@@ -1,3 +1,33 @@
1+
2013-10-02 Pedro Alves <palves@redhat.com>
2+
3+
* cp-valprint.c (cp_print_value_fields): Adjust calls to
4+
val_print_optimized_out.
5+
* jv-valprint.c (java_print_value_fields): Likewise.
6+
* p-valprint.c (pascal_object_print_value_fields): Likewise.
7+
* dwarf2loc.c (dwarf2_evaluate_loc_desc_full)
8+
<DWARF_VALUE_REGISTER>: If the register was not saved, return a
9+
new optimized out value.
10+
* findvar.c (address_from_register): Likewise.
11+
* frame.c (put_frame_register): Tweak error string to say the
12+
register was not saved, rather than optimized out.
13+
* infcmd.c (default_print_one_register_info): Adjust call to
14+
val_print_optimized_out. Use value_of_register instead of
15+
get_frame_register_value.
16+
* mi/mi-main.c (output_register): Use value_of_register instead of
17+
get_frame_register_value.
18+
* valprint.c (valprint_check_validity): Likewise.
19+
(val_print_optimized_out): New value parameter. If the value is
20+
lval_register, print <not saved> instead.
21+
(value_check_printable, val_print_scalar_formatted): Adjust calls
22+
to val_print_optimized_out.
23+
* valprint.h (val_print_optimized_out): New value parameter.
24+
* value.c (struct value) <optimized_out>: Extend comment.
25+
(error_value_optimized_out): New function.
26+
(require_not_optimized_out): Use it. Use a different string for
27+
lval_register values.
28+
* value.h (error_value_optimized_out): New declaration.
29+
* NEWS: Mention <not saved>.
30+
131
2013-10-02 Joel Brobecker <brobecker@adacore.com>
232

333
* symtab.c (compare_search_syms): Use FILENAME_CMP instead of

‎gdb/NEWS

+14
Original file line numberDiff line numberDiff line change
@@ -15,6 +15,20 @@
1515

1616
* The "catch syscall" command now works on arm*-linux* targets.
1717

18+
* GDB now consistently shows "<not saved>" when printing values of
19+
registers the debug info indicates have not been saved in the frame
20+
and there's nowhere to retrieve them from
21+
(callee-saved/call-clobbered registers):
22+
23+
(gdb) p $rax
24+
$1 = <not saved>
25+
26+
(gdb) info registers rax
27+
rax <not saved>
28+
29+
Before, the former would print "<optimized out>", and the latter
30+
"*value not available*".
31+
1832
* Python scripting
1933

2034
** Frame filters and frame decorators have been added.

‎gdb/cp-valprint.c

+2-2
Original file line numberDiff line numberDiff line change
@@ -298,7 +298,7 @@ cp_print_value_fields (struct type *type, struct type *real_type,
298298
TYPE_FIELD_BITPOS (type, i),
299299
TYPE_FIELD_BITSIZE (type, i)))
300300
{
301-
val_print_optimized_out (stream);
301+
val_print_optimized_out (val, stream);
302302
}
303303
else
304304
{
@@ -334,7 +334,7 @@ cp_print_value_fields (struct type *type, struct type *real_type,
334334
_("<error reading variable: %s>"),
335335
ex.message);
336336
else if (v == NULL)
337-
val_print_optimized_out (stream);
337+
val_print_optimized_out (NULL, stream);
338338
else
339339
cp_print_static_field (TYPE_FIELD_TYPE (type, i),
340340
v, stream, recurse + 1,

‎gdb/doc/ChangeLog

+5
Original file line numberDiff line numberDiff line change
@@ -1,3 +1,8 @@
1+
2013-10-02 Pedro Alves <palves@redhat.com>
2+
3+
* gdb.texinfo (Registers): Expand description of saved registers
4+
in frames. Explain <not saved>.
5+
16
2013-09-25 Doug Evans <dje@google.com>
27

38
* gdb.texinfo (Debugging Output): Document set/show debug symfile.

‎gdb/doc/gdb.texinfo

+27-4
Original file line numberDiff line numberDiff line change
@@ -10031,10 +10031,33 @@ were exited and their saved registers restored. In order to see the
1003110031
true contents of hardware registers, you must select the innermost
1003210032
frame (with @samp{frame 0}).
1003310033

10034-
However, @value{GDBN} must deduce where registers are saved, from the machine
10035-
code generated by your compiler. If some registers are not saved, or if
10036-
@value{GDBN} is unable to locate the saved registers, the selected stack
10037-
frame makes no difference.
10034+
@cindex caller-saved registers
10035+
@cindex call-clobbered registers
10036+
@cindex volatile registers
10037+
@cindex <not saved> values
10038+
Usually ABIs reserve some registers as not needed to be saved by the
10039+
callee (a.k.a.: ``caller-saved'', ``call-clobbered'' or ``volatile''
10040+
registers). It may therefore not be possible for @value{GDBN} to know
10041+
the value a register had before the call (in other words, in the outer
10042+
frame), if the register value has since been changed by the callee.
10043+
@value{GDBN} tries to deduce where the inner frame saved
10044+
(``callee-saved'') registers, from the debug info, unwind info, or the
10045+
machine code generated by your compiler. If some register is not
10046+
saved, and @value{GDBN} knows the register is ``caller-saved'' (via
10047+
its own knowledge of the ABI, or because the debug/unwind info
10048+
explicitly says the register's value is undefined), @value{GDBN}
10049+
displays @w{@samp{<not saved>}} as the register's value. With targets
10050+
that @value{GDBN} has no knowledge of the register saving convention,
10051+
if a register was not saved by the callee, then its value and location
10052+
in the outer frame are assumed to be the same of the inner frame.
10053+
This is usually harmless, because if the register is call-clobbered,
10054+
the caller either does not care what is in the register after the
10055+
call, or has code to restore the value that it does care about. Note,
10056+
however, that if you change such a register in the outer frame, you
10057+
may also be affecting the inner frame. Also, the more ``outer'' the
10058+
frame is you're looking at, the more likely a call-clobbered
10059+
register's value is to be wrong, in the sense that it doesn't actually
10060+
represent the value the register had just before the call.
1003810061

1003910062
@node Floating Point Hardware
1004010063
@section Floating Point Hardware

‎gdb/dwarf2loc.c

+13-3
Original file line numberDiff line numberDiff line change
@@ -2290,11 +2290,21 @@ dwarf2_evaluate_loc_desc_full (struct type *type, struct frame_info *frame,
22902290
if (byte_offset != 0)
22912291
error (_("cannot use offset on synthetic pointer to register"));
22922292
do_cleanups (value_chain);
2293-
if (gdb_regnum != -1)
2294-
retval = value_from_register (type, gdb_regnum, frame);
2295-
else
2293+
if (gdb_regnum == -1)
22962294
error (_("Unable to access DWARF register number %d"),
22972295
dwarf_regnum);
2296+
retval = value_from_register (type, gdb_regnum, frame);
2297+
if (value_optimized_out (retval))
2298+
{
2299+
/* This means the register has undefined value / was
2300+
not saved. As we're computing the location of some
2301+
variable etc. in the program, not a value for
2302+
inspecting a register ($pc, $sp, etc.), return a
2303+
generic optimized out value instead, so that we show
2304+
<optimized out> instead of <not saved>. */
2305+
do_cleanups (value_chain);
2306+
retval = allocate_optimized_out_value (type);
2307+
}
22982308
}
22992309
break;
23002310

‎gdb/findvar.c

+9
Original file line numberDiff line numberDiff line change
@@ -757,6 +757,15 @@ address_from_register (struct type *type, int regnum, struct frame_info *frame)
757757
value = value_from_register (type, regnum, frame);
758758
gdb_assert (value);
759759

760+
if (value_optimized_out (value))
761+
{
762+
/* This function is used while computing a location expression.
763+
Complain about the value being optimized out, rather than
764+
letting value_as_address complain about some random register
765+
the expression depends on not being saved. */
766+
error_value_optimized_out ();
767+
}
768+
760769
result = value_as_address (value);
761770
release_value (value);
762771
value_free (value);

‎gdb/frame.c

+1-1
Original file line numberDiff line numberDiff line change
@@ -1143,7 +1143,7 @@ put_frame_register (struct frame_info *frame, int regnum,
11431143
frame_register (frame, regnum, &optim, &unavail,
11441144
&lval, &addr, &realnum, NULL);
11451145
if (optim)
1146-
error (_("Attempt to assign to a value that was optimized out."));
1146+
error (_("Attempt to assign to a register that was not saved."));
11471147
switch (lval)
11481148
{
11491149
case lval_memory:

‎gdb/infcmd.c

+2-2
Original file line numberDiff line numberDiff line change
@@ -2035,7 +2035,7 @@ default_print_one_register_info (struct ui_file *file,
20352035
}
20362036
else if (value_optimized_out (val))
20372037
{
2038-
val_print_optimized_out (file);
2038+
val_print_optimized_out (val, file);
20392039
fprintf_filtered (file, "\n");
20402040
return;
20412041
}
@@ -2142,7 +2142,7 @@ default_print_registers_info (struct gdbarch *gdbarch,
21422142

21432143
default_print_one_register_info (file,
21442144
gdbarch_register_name (gdbarch, i),
2145-
get_frame_register_value (frame, i));
2145+
value_of_register (i, frame));
21462146
}
21472147
}
21482148

‎gdb/jv-valprint.c

+2-2
Original file line numberDiff line numberDiff line change
@@ -395,7 +395,7 @@ java_print_value_fields (struct type *type, const gdb_byte *valaddr,
395395
else if (!value_bits_valid (val, TYPE_FIELD_BITPOS (type, i),
396396
TYPE_FIELD_BITSIZE (type, i)))
397397
{
398-
val_print_optimized_out (stream);
398+
val_print_optimized_out (val, stream);
399399
}
400400
else
401401
{
@@ -420,7 +420,7 @@ java_print_value_fields (struct type *type, const gdb_byte *valaddr,
420420
struct value *v = value_static_field (type, i);
421421

422422
if (v == NULL)
423-
val_print_optimized_out (stream);
423+
val_print_optimized_out (NULL, stream);
424424
else
425425
{
426426
struct value_print_options opts;

‎gdb/mi/mi-main.c

+1-1
Original file line numberDiff line numberDiff line change
@@ -1161,7 +1161,7 @@ output_register (struct frame_info *frame, int regnum, int format,
11611161
{
11621162
struct gdbarch *gdbarch = get_frame_arch (frame);
11631163
struct ui_out *uiout = current_uiout;
1164-
struct value *val = get_frame_register_value (frame, regnum);
1164+
struct value *val = value_of_register (regnum, frame);
11651165
struct cleanup *tuple_cleanup;
11661166
struct value_print_options opts;
11671167
struct ui_file *stb;

‎gdb/p-valprint.c

+2-2
Original file line numberDiff line numberDiff line change
@@ -629,7 +629,7 @@ pascal_object_print_value_fields (struct type *type, const gdb_byte *valaddr,
629629
else if (!value_bits_valid (val, TYPE_FIELD_BITPOS (type, i),
630630
TYPE_FIELD_BITSIZE (type, i)))
631631
{
632-
val_print_optimized_out (stream);
632+
val_print_optimized_out (val, stream);
633633
}
634634
else
635635
{
@@ -657,7 +657,7 @@ pascal_object_print_value_fields (struct type *type, const gdb_byte *valaddr,
657657
v = value_field_bitfield (type, i, valaddr, offset, val);
658658

659659
if (v == NULL)
660-
val_print_optimized_out (stream);
660+
val_print_optimized_out (NULL, stream);
661661
else
662662
pascal_object_print_static_field (v, stream, recurse + 1,
663663
options);

‎gdb/testsuite/ChangeLog

+8
Original file line numberDiff line numberDiff line change
@@ -1,3 +1,11 @@
1+
2013-10-02 Pedro Alves <palves@redhat.com>
2+
3+
* gdb.dwarf2/dw2-reg-undefined.exp <pattern_rax_rbx_rcx_print,
4+
pattern_rax_rbx_rcx_info>: Set to "<not saved>".
5+
* gdb.mi/mi-reg-undefined.exp (opt_out_pattern): Delete.
6+
(not_saved_pattern): New.
7+
Replace use of the former with the latter.
8+
19
2013-10-02 Pedro Alves <palves@redhat.com>
210

311
* README (Board Settings): Document "exit_is_reliable".

‎gdb/testsuite/gdb.dwarf2/dw2-reg-undefined.exp

+2-2
Original file line numberDiff line numberDiff line change
@@ -45,8 +45,8 @@ for {set f 0} {$f < 3} {incr f} {
4545
set pattern_r8_r9_print "$hex"
4646
set pattern_r8_r9_info "$hex\\s+$decimal"
4747
} else {
48-
set pattern_rax_rbx_rcx_print "<optimized out>"
49-
set pattern_rax_rbx_rcx_info "<optimized out>"
48+
set pattern_rax_rbx_rcx_print "<not saved>"
49+
set pattern_rax_rbx_rcx_info "<not saved>"
5050
set pattern_r8_r9_print "$hex"
5151
set pattern_r8_r9_info "$hex\\s+$decimal"
5252
}

‎gdb/testsuite/gdb.mi/mi-reg-undefined.exp

+2-2
Original file line numberDiff line numberDiff line change
@@ -52,13 +52,13 @@ mi_gdb_test "111-stack-list-frames" \
5252
"111\\^done,stack=\\\[frame=\{level=\"0\",addr=\"$hex\",func=\"stop_frame\",.*\},frame=\{level=\"1\",addr=\"$hex\",func=\"first_frame\",.*\},frame=\{level=\"2\",addr=\"$hex\",func=\"main\",.*\}\\\]" \
5353
"stack frame listing"
5454

55-
set opt_out_pattern "<optimized out>"
55+
set not_saved_pattern "<not saved>"
5656

5757
for {set f 0} {$f < 3} {incr f} {
5858
if {${f} == 0} {
5959
set pattern_0_1_2 ${hex}
6060
} else {
61-
set pattern_0_1_2 ${opt_out_pattern}
61+
set pattern_0_1_2 ${not_saved_pattern}
6262
}
6363

6464
mi_gdb_test "22${f}-data-list-register-values --thread 1 --frame ${f} x 0 1 2 8 9" \

‎gdb/valprint.c

+8-5
Original file line numberDiff line numberDiff line change
@@ -314,7 +314,7 @@ valprint_check_validity (struct ui_file *stream,
314314
if (!value_bits_valid (val, TARGET_CHAR_BIT * embedded_offset,
315315
TARGET_CHAR_BIT * TYPE_LENGTH (type)))
316316
{
317-
val_print_optimized_out (stream);
317+
val_print_optimized_out (val, stream);
318318
return 0;
319319
}
320320

@@ -336,9 +336,12 @@ valprint_check_validity (struct ui_file *stream,
336336
}
337337

338338
void
339-
val_print_optimized_out (struct ui_file *stream)
339+
val_print_optimized_out (const struct value *val, struct ui_file *stream)
340340
{
341-
fprintf_filtered (stream, _("<optimized out>"));
341+
if (val != NULL && value_lval_const (val) == lval_register)
342+
fprintf_filtered (stream, _("<not saved>"));
343+
else
344+
fprintf_filtered (stream, _("<optimized out>"));
342345
}
343346

344347
void
@@ -805,7 +808,7 @@ value_check_printable (struct value *val, struct ui_file *stream,
805808
if (options->summary && !val_print_scalar_type_p (value_type (val)))
806809
fprintf_filtered (stream, "...");
807810
else
808-
val_print_optimized_out (stream);
811+
val_print_optimized_out (val, stream);
809812
return 0;
810813
}
811814

@@ -966,7 +969,7 @@ val_print_scalar_formatted (struct type *type,
966969
printed, because all bits contribute to its representation. */
967970
if (!value_bits_valid (val, TARGET_CHAR_BIT * embedded_offset,
968971
TARGET_CHAR_BIT * TYPE_LENGTH (type)))
969-
val_print_optimized_out (stream);
972+
val_print_optimized_out (val, stream);
970973
else if (!value_bytes_available (val, embedded_offset, TYPE_LENGTH (type)))
971974
val_print_unavailable (stream);
972975
else

‎gdb/valprint.h

+2-1
Original file line numberDiff line numberDiff line change
@@ -160,7 +160,8 @@ extern int read_string (CORE_ADDR addr, int len, int width,
160160
enum bfd_endian byte_order, gdb_byte **buffer,
161161
int *bytes_read);
162162

163-
extern void val_print_optimized_out (struct ui_file *stream);
163+
extern void val_print_optimized_out (const struct value *val,
164+
struct ui_file *stream);
164165

165166
extern void val_print_unavailable (struct ui_file *stream);
166167

‎gdb/value.c

+19-3
Original file line numberDiff line numberDiff line change
@@ -197,8 +197,13 @@ struct value
197197
reset, be sure to consider this use as well! */
198198
unsigned int lazy : 1;
199199

200-
/* If nonzero, this is the value of a variable which does not
201-
actually exist in the program. */
200+
/* If nonzero, this is the value of a variable that does not
201+
actually exist in the program. If nonzero, and LVAL is
202+
lval_register, this is a register ($pc, $sp, etc., never a
203+
program variable) that has not been saved in the frame. All
204+
optimized-out values are treated pretty much the same, except
205+
registers have a different string representation and related
206+
error strings. */
202207
unsigned int optimized_out : 1;
203208

204209
/* If value is a variable, is it initialized or not. */
@@ -902,11 +907,22 @@ value_actual_type (struct value *value, int resolve_simple_types,
902907
return result;
903908
}
904909

910+
void
911+
error_value_optimized_out (void)
912+
{
913+
error (_("value has been optimized out"));
914+
}
915+
905916
static void
906917
require_not_optimized_out (const struct value *value)
907918
{
908919
if (value->optimized_out)
909-
error (_("value has been optimized out"));
920+
{
921+
if (value->lval == lval_register)
922+
error (_("register has not been saved in frame"));
923+
else
924+
error_value_optimized_out ();
925+
}
910926
}
911927

912928
static void

‎gdb/value.h

+5
Original file line numberDiff line numberDiff line change
@@ -273,6 +273,11 @@ extern void set_value_lazy (struct value *value, int val);
273273
extern int value_stack (struct value *);
274274
extern void set_value_stack (struct value *value, int val);
275275

276+
/* Throw an error complaining that the value has been optimized
277+
out. */
278+
279+
extern void error_value_optimized_out (void);
280+
276281
/* value_contents() and value_contents_raw() both return the address
277282
of the gdb buffer used to hold a copy of the contents of the lval.
278283
value_contents() is used when the contents of the buffer are needed

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