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binutils-gdb/gdb/findvar.c
Pedro Alves d5b495b40b Rework value_of_register in terms of value_of_register_lazy. 
I noticed that value_of_register (used for getting values _of_
registers ($pc, $rax, etc.), rather than variables _in_ registers),
kind of builds a franken-value, by propagating the lval and address of
the frame register value, but not the entire location, like necessary
for lval_computed (if some unwinder ever returns that, the resulting
value will misbehave).  This gets in the way of printing optimized out
(not saved) lval_registers differently from other optimized out
values, as it doesn't make sure the resulting value is lval_register.

I started out by just doing something like:

-  VALUE_LVAL (reg_val) = lval;
-  set_value_address (reg_val, addr);
+  VALUE_LVAL (reg_val) = lval_register;

... just like value_of_register_lazy below.  That's sufficient to fix
the issue.

Then I noticed this is using frame_register, which we should avoid
nowadays, for it returns elements of a value, but not all that's
sometimes necessary (unavailable-ness is all or nothing with it, for
instance), and considered using get_frame_register_value instead
(which returns a struct value), and value_contents_copy, just like
value_fetch_lazy's handling of lval_register.  But at that point, I
realized we might as well just defer all that work to
value_of_register_lazy/value_fetch_lazy...

Doing it this way adds a frame_find_by_id lookup (from within
value_fetch_lazy), while we already have a frame pointer handy in
value_of_register.  I considered factoring out the lazy register
fetching out of value_fetch_lazy, into a function that takes a frame
pointer and call that instead, avoiding the lookup, but then it looked
like too much complication for an early optimization, and went back to
keeping it simple.

Tested on x86_64 Fedora 17.

gdb/
2013-09-05  Pedro Alves  <palves@redhat.com>

	* findvar.c (value_of_register): Rework in terms of
	value_of_register_lazy.
2013-09-05 14:02:16 +00:00

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/* Find a variable's value in memory, for GDB, the GNU debugger.
Copyright (C) 1986-2013 Free Software Foundation, Inc.
This file is part of GDB.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
#include "defs.h"
#include "symtab.h"
#include "gdbtypes.h"
#include "frame.h"
#include "value.h"
#include "gdbcore.h"
#include "inferior.h"
#include "target.h"
#include "gdb_string.h"
#include "gdb_assert.h"
#include "floatformat.h"
#include "symfile.h" /* for overlay functions */
#include "regcache.h"
#include "user-regs.h"
#include "block.h"
#include "objfiles.h"
#include "language.h"
/* Basic byte-swapping routines. All 'extract' functions return a
host-format integer from a target-format integer at ADDR which is
LEN bytes long. */
#if TARGET_CHAR_BIT != 8 || HOST_CHAR_BIT != 8
/* 8 bit characters are a pretty safe assumption these days, so we
assume it throughout all these swapping routines. If we had to deal with
9 bit characters, we would need to make len be in bits and would have
to re-write these routines... */
you lose
#endif
LONGEST
extract_signed_integer (const gdb_byte *addr, int len,
enum bfd_endian byte_order)
{
LONGEST retval;
const unsigned char *p;
const unsigned char *startaddr = addr;
const unsigned char *endaddr = startaddr + len;
if (len > (int) sizeof (LONGEST))
error (_("\
That operation is not available on integers of more than %d bytes."),
(int) sizeof (LONGEST));
/* Start at the most significant end of the integer, and work towards
the least significant. */
if (byte_order == BFD_ENDIAN_BIG)
{
p = startaddr;
/* Do the sign extension once at the start. */
retval = ((LONGEST) * p ^ 0x80) - 0x80;
for (++p; p < endaddr; ++p)
retval = (retval << 8) | *p;
}
else
{
p = endaddr - 1;
/* Do the sign extension once at the start. */
retval = ((LONGEST) * p ^ 0x80) - 0x80;
for (--p; p >= startaddr; --p)
retval = (retval << 8) | *p;
}
return retval;
}
ULONGEST
extract_unsigned_integer (const gdb_byte *addr, int len,
enum bfd_endian byte_order)
{
ULONGEST retval;
const unsigned char *p;
const unsigned char *startaddr = addr;
const unsigned char *endaddr = startaddr + len;
if (len > (int) sizeof (ULONGEST))
error (_("\
That operation is not available on integers of more than %d bytes."),
(int) sizeof (ULONGEST));
/* Start at the most significant end of the integer, and work towards
the least significant. */
retval = 0;
if (byte_order == BFD_ENDIAN_BIG)
{
for (p = startaddr; p < endaddr; ++p)
retval = (retval << 8) | *p;
}
else
{
for (p = endaddr - 1; p >= startaddr; --p)
retval = (retval << 8) | *p;
}
return retval;
}
/* Sometimes a long long unsigned integer can be extracted as a
LONGEST value. This is done so that we can print these values
better. If this integer can be converted to a LONGEST, this
function returns 1 and sets *PVAL. Otherwise it returns 0. */
int
extract_long_unsigned_integer (const gdb_byte *addr, int orig_len,
enum bfd_endian byte_order, LONGEST *pval)
{
const gdb_byte *p;
const gdb_byte *first_addr;
int len;
len = orig_len;
if (byte_order == BFD_ENDIAN_BIG)
{
for (p = addr;
len > (int) sizeof (LONGEST) && p < addr + orig_len;
p++)
{
if (*p == 0)
len--;
else
break;
}
first_addr = p;
}
else
{
first_addr = addr;
for (p = addr + orig_len - 1;
len > (int) sizeof (LONGEST) && p >= addr;
p--)
{
if (*p == 0)
len--;
else
break;
}
}
if (len <= (int) sizeof (LONGEST))
{
*pval = (LONGEST) extract_unsigned_integer (first_addr,
sizeof (LONGEST),
byte_order);
return 1;
}
return 0;
}
/* Treat the bytes at BUF as a pointer of type TYPE, and return the
address it represents. */
CORE_ADDR
extract_typed_address (const gdb_byte *buf, struct type *type)
{
if (TYPE_CODE (type) != TYPE_CODE_PTR
&& TYPE_CODE (type) != TYPE_CODE_REF)
internal_error (__FILE__, __LINE__,
_("extract_typed_address: "
"type is not a pointer or reference"));
return gdbarch_pointer_to_address (get_type_arch (type), type, buf);
}
/* All 'store' functions accept a host-format integer and store a
target-format integer at ADDR which is LEN bytes long. */
void
store_signed_integer (gdb_byte *addr, int len,
enum bfd_endian byte_order, LONGEST val)
{
gdb_byte *p;
gdb_byte *startaddr = addr;
gdb_byte *endaddr = startaddr + len;
/* Start at the least significant end of the integer, and work towards
the most significant. */
if (byte_order == BFD_ENDIAN_BIG)
{
for (p = endaddr - 1; p >= startaddr; --p)
{
*p = val & 0xff;
val >>= 8;
}
}
else
{
for (p = startaddr; p < endaddr; ++p)
{
*p = val & 0xff;
val >>= 8;
}
}
}
void
store_unsigned_integer (gdb_byte *addr, int len,
enum bfd_endian byte_order, ULONGEST val)
{
unsigned char *p;
unsigned char *startaddr = (unsigned char *) addr;
unsigned char *endaddr = startaddr + len;
/* Start at the least significant end of the integer, and work towards
the most significant. */
if (byte_order == BFD_ENDIAN_BIG)
{
for (p = endaddr - 1; p >= startaddr; --p)
{
*p = val & 0xff;
val >>= 8;
}
}
else
{
for (p = startaddr; p < endaddr; ++p)
{
*p = val & 0xff;
val >>= 8;
}
}
}
/* Store the address ADDR as a pointer of type TYPE at BUF, in target
form. */
void
store_typed_address (gdb_byte *buf, struct type *type, CORE_ADDR addr)
{
if (TYPE_CODE (type) != TYPE_CODE_PTR
&& TYPE_CODE (type) != TYPE_CODE_REF)
internal_error (__FILE__, __LINE__,
_("store_typed_address: "
"type is not a pointer or reference"));
gdbarch_address_to_pointer (get_type_arch (type), type, buf, addr);
}
/* Return a `value' with the contents of (virtual or cooked) register
REGNUM as found in the specified FRAME. The register's type is
determined by register_type(). */
struct value *
value_of_register (int regnum, struct frame_info *frame)
{
struct gdbarch *gdbarch = get_frame_arch (frame);
struct value *reg_val;
/* User registers lie completely outside of the range of normal
registers. Catch them early so that the target never sees them. */
if (regnum >= gdbarch_num_regs (gdbarch)
+ gdbarch_num_pseudo_regs (gdbarch))
return value_of_user_reg (regnum, frame);
reg_val = value_of_register_lazy (frame, regnum);
value_fetch_lazy (reg_val);
return reg_val;
}
/* Return a `value' with the contents of (virtual or cooked) register
REGNUM as found in the specified FRAME. The register's type is
determined by register_type(). The value is not fetched. */
struct value *
value_of_register_lazy (struct frame_info *frame, int regnum)
{
struct gdbarch *gdbarch = get_frame_arch (frame);
struct value *reg_val;
gdb_assert (regnum < (gdbarch_num_regs (gdbarch)
+ gdbarch_num_pseudo_regs (gdbarch)));
/* We should have a valid (i.e. non-sentinel) frame. */
gdb_assert (frame_id_p (get_frame_id (frame)));
reg_val = allocate_value_lazy (register_type (gdbarch, regnum));
VALUE_LVAL (reg_val) = lval_register;
VALUE_REGNUM (reg_val) = regnum;
VALUE_FRAME_ID (reg_val) = get_frame_id (frame);
return reg_val;
}
/* Given a pointer of type TYPE in target form in BUF, return the
address it represents. */
CORE_ADDR
unsigned_pointer_to_address (struct gdbarch *gdbarch,
struct type *type, const gdb_byte *buf)
{
enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
return extract_unsigned_integer (buf, TYPE_LENGTH (type), byte_order);
}
CORE_ADDR
signed_pointer_to_address (struct gdbarch *gdbarch,
struct type *type, const gdb_byte *buf)
{
enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
return extract_signed_integer (buf, TYPE_LENGTH (type), byte_order);
}
/* Given an address, store it as a pointer of type TYPE in target
format in BUF. */
void
unsigned_address_to_pointer (struct gdbarch *gdbarch, struct type *type,
gdb_byte *buf, CORE_ADDR addr)
{
enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
store_unsigned_integer (buf, TYPE_LENGTH (type), byte_order, addr);
}
void
address_to_signed_pointer (struct gdbarch *gdbarch, struct type *type,
gdb_byte *buf, CORE_ADDR addr)
{
enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
store_signed_integer (buf, TYPE_LENGTH (type), byte_order, addr);
}
/* Will calling read_var_value or locate_var_value on SYM end
up caring what frame it is being evaluated relative to? SYM must
be non-NULL. */
int
symbol_read_needs_frame (struct symbol *sym)
{
if (SYMBOL_COMPUTED_OPS (sym) != NULL)
return SYMBOL_COMPUTED_OPS (sym)->read_needs_frame (sym);
switch (SYMBOL_CLASS (sym))
{
/* All cases listed explicitly so that gcc -Wall will detect it if
we failed to consider one. */
case LOC_COMPUTED:
gdb_assert_not_reached (_("LOC_COMPUTED variable missing a method"));
case LOC_REGISTER:
case LOC_ARG:
case LOC_REF_ARG:
case LOC_REGPARM_ADDR:
case LOC_LOCAL:
return 1;
case LOC_UNDEF:
case LOC_CONST:
case LOC_STATIC:
case LOC_TYPEDEF:
case LOC_LABEL:
/* Getting the address of a label can be done independently of the block,
even if some *uses* of that address wouldn't work so well without
the right frame. */
case LOC_BLOCK:
case LOC_CONST_BYTES:
case LOC_UNRESOLVED:
case LOC_OPTIMIZED_OUT:
return 0;
}
return 1;
}
/* Private data to be used with minsym_lookup_iterator_cb. */
struct minsym_lookup_data
{
/* The name of the minimal symbol we are searching for. */
const char *name;
/* The field where the callback should store the minimal symbol
if found. It should be initialized to NULL before the search
is started. */
struct minimal_symbol *result;
/* The objfile in which the symbol was found. */
struct objfile *objfile;
};
/* A callback function for gdbarch_iterate_over_objfiles_in_search_order.
It searches by name for a minimal symbol within the given OBJFILE.
The arguments are passed via CB_DATA, which in reality is a pointer
to struct minsym_lookup_data. */
static int
minsym_lookup_iterator_cb (struct objfile *objfile, void *cb_data)
{
struct minsym_lookup_data *data = (struct minsym_lookup_data *) cb_data;
gdb_assert (data->result == NULL);
data->result = lookup_minimal_symbol (data->name, NULL, objfile);
data->objfile = objfile;
/* The iterator should stop iff a match was found. */
return (data->result != NULL);
}
/* A default implementation for the "la_read_var_value" hook in
the language vector which should work in most situations. */
struct value *
default_read_var_value (struct symbol *var, struct frame_info *frame)
{
struct value *v;
struct type *type = SYMBOL_TYPE (var);
CORE_ADDR addr;
/* Call check_typedef on our type to make sure that, if TYPE is
a TYPE_CODE_TYPEDEF, its length is set to the length of the target type
instead of zero. However, we do not replace the typedef type by the
target type, because we want to keep the typedef in order to be able to
set the returned value type description correctly. */
check_typedef (type);
if (symbol_read_needs_frame (var))
gdb_assert (frame);
if (SYMBOL_COMPUTED_OPS (var) != NULL)
return SYMBOL_COMPUTED_OPS (var)->read_variable (var, frame);
switch (SYMBOL_CLASS (var))
{
case LOC_CONST:
/* Put the constant back in target format. */
v = allocate_value (type);
store_signed_integer (value_contents_raw (v), TYPE_LENGTH (type),
gdbarch_byte_order (get_type_arch (type)),
(LONGEST) SYMBOL_VALUE (var));
VALUE_LVAL (v) = not_lval;
return v;
case LOC_LABEL:
/* Put the constant back in target format. */
v = allocate_value (type);
if (overlay_debugging)
{
CORE_ADDR addr
= symbol_overlayed_address (SYMBOL_VALUE_ADDRESS (var),
SYMBOL_OBJ_SECTION (SYMBOL_OBJFILE (var),
var));
store_typed_address (value_contents_raw (v), type, addr);
}
else
store_typed_address (value_contents_raw (v), type,
SYMBOL_VALUE_ADDRESS (var));
VALUE_LVAL (v) = not_lval;
return v;
case LOC_CONST_BYTES:
v = allocate_value (type);
memcpy (value_contents_raw (v), SYMBOL_VALUE_BYTES (var),
TYPE_LENGTH (type));
VALUE_LVAL (v) = not_lval;
return v;
case LOC_STATIC:
if (overlay_debugging)
addr = symbol_overlayed_address (SYMBOL_VALUE_ADDRESS (var),
SYMBOL_OBJ_SECTION (SYMBOL_OBJFILE (var),
var));
else
addr = SYMBOL_VALUE_ADDRESS (var);
break;
case LOC_ARG:
addr = get_frame_args_address (frame);
if (!addr)
error (_("Unknown argument list address for `%s'."),
SYMBOL_PRINT_NAME (var));
addr += SYMBOL_VALUE (var);
break;
case LOC_REF_ARG:
{
struct value *ref;
CORE_ADDR argref;
argref = get_frame_args_address (frame);
if (!argref)
error (_("Unknown argument list address for `%s'."),
SYMBOL_PRINT_NAME (var));
argref += SYMBOL_VALUE (var);
ref = value_at (lookup_pointer_type (type), argref);
addr = value_as_address (ref);
break;
}
case LOC_LOCAL:
addr = get_frame_locals_address (frame);
addr += SYMBOL_VALUE (var);
break;
case LOC_TYPEDEF:
error (_("Cannot look up value of a typedef `%s'."),
SYMBOL_PRINT_NAME (var));
break;
case LOC_BLOCK:
if (overlay_debugging)
addr = symbol_overlayed_address
(BLOCK_START (SYMBOL_BLOCK_VALUE (var)), SYMBOL_OBJ_SECTION (SYMBOL_OBJFILE (var),
var));
else
addr = BLOCK_START (SYMBOL_BLOCK_VALUE (var));
break;
case LOC_REGISTER:
case LOC_REGPARM_ADDR:
{
int regno = SYMBOL_REGISTER_OPS (var)
->register_number (var, get_frame_arch (frame));
struct value *regval;
if (SYMBOL_CLASS (var) == LOC_REGPARM_ADDR)
{
regval = value_from_register (lookup_pointer_type (type),
regno,
frame);
if (regval == NULL)
error (_("Value of register variable not available for `%s'."),
SYMBOL_PRINT_NAME (var));
addr = value_as_address (regval);
}
else
{
regval = value_from_register (type, regno, frame);
if (regval == NULL)
error (_("Value of register variable not available for `%s'."),
SYMBOL_PRINT_NAME (var));
return regval;
}
}
break;
case LOC_COMPUTED:
gdb_assert_not_reached (_("LOC_COMPUTED variable missing a method"));
case LOC_UNRESOLVED:
{
struct minsym_lookup_data lookup_data;
struct minimal_symbol *msym;
struct obj_section *obj_section;
memset (&lookup_data, 0, sizeof (lookup_data));
lookup_data.name = SYMBOL_LINKAGE_NAME (var);
gdbarch_iterate_over_objfiles_in_search_order
(get_objfile_arch (SYMBOL_SYMTAB (var)->objfile),
minsym_lookup_iterator_cb, &lookup_data,
SYMBOL_SYMTAB (var)->objfile);
msym = lookup_data.result;
if (msym == NULL)
error (_("No global symbol \"%s\"."), SYMBOL_LINKAGE_NAME (var));
if (overlay_debugging)
addr = symbol_overlayed_address (SYMBOL_VALUE_ADDRESS (msym),
SYMBOL_OBJ_SECTION (lookup_data.objfile,
msym));
else
addr = SYMBOL_VALUE_ADDRESS (msym);
obj_section = SYMBOL_OBJ_SECTION (lookup_data.objfile, msym);
if (obj_section
&& (obj_section->the_bfd_section->flags & SEC_THREAD_LOCAL) != 0)
addr = target_translate_tls_address (obj_section->objfile, addr);
}
break;
case LOC_OPTIMIZED_OUT:
return allocate_optimized_out_value (type);
default:
error (_("Cannot look up value of a botched symbol `%s'."),
SYMBOL_PRINT_NAME (var));
break;
}
v = value_at_lazy (type, addr);
return v;
}
/* Calls VAR's language la_read_var_value hook with the given arguments. */
struct value *
read_var_value (struct symbol *var, struct frame_info *frame)
{
const struct language_defn *lang = language_def (SYMBOL_LANGUAGE (var));
gdb_assert (lang != NULL);
gdb_assert (lang->la_read_var_value != NULL);
return lang->la_read_var_value (var, frame);
}
/* Install default attributes for register values. */
struct value *
default_value_from_register (struct type *type, int regnum,
struct frame_info *frame)
{
struct gdbarch *gdbarch = get_frame_arch (frame);
int len = TYPE_LENGTH (type);
struct value *value = allocate_value (type);
VALUE_LVAL (value) = lval_register;
VALUE_FRAME_ID (value) = get_frame_id (frame);
VALUE_REGNUM (value) = regnum;
/* Any structure stored in more than one register will always be
an integral number of registers. Otherwise, you need to do
some fiddling with the last register copied here for little
endian machines. */
if (gdbarch_byte_order (gdbarch) == BFD_ENDIAN_BIG
&& len < register_size (gdbarch, regnum))
/* Big-endian, and we want less than full size. */
set_value_offset (value, register_size (gdbarch, regnum) - len);
else
set_value_offset (value, 0);
return value;
}
/* VALUE must be an lval_register value. If regnum is the value's
associated register number, and len the length of the values type,
read one or more registers in FRAME, starting with register REGNUM,
until we've read LEN bytes.
If any of the registers we try to read are optimized out, then mark the
complete resulting value as optimized out. */
void
read_frame_register_value (struct value *value, struct frame_info *frame)
{
struct gdbarch *gdbarch = get_frame_arch (frame);
int offset = 0;
int reg_offset = value_offset (value);
int regnum = VALUE_REGNUM (value);
int len = TYPE_LENGTH (check_typedef (value_type (value)));
gdb_assert (VALUE_LVAL (value) == lval_register);
/* Skip registers wholly inside of REG_OFFSET. */
while (reg_offset >= register_size (gdbarch, regnum))
{
reg_offset -= register_size (gdbarch, regnum);
regnum++;
}
/* Copy the data. */
while (len > 0)
{
struct value *regval = get_frame_register_value (frame, regnum);
int reg_len = TYPE_LENGTH (value_type (regval)) - reg_offset;
if (value_optimized_out (regval))
{
set_value_optimized_out (value, 1);
break;
}
/* If the register length is larger than the number of bytes
remaining to copy, then only copy the appropriate bytes. */
if (reg_len > len)
reg_len = len;
value_contents_copy (value, offset, regval, reg_offset, reg_len);
offset += reg_len;
len -= reg_len;
reg_offset = 0;
regnum++;
}
}
/* Return a value of type TYPE, stored in register REGNUM, in frame FRAME. */
struct value *
value_from_register (struct type *type, int regnum, struct frame_info *frame)
{
struct gdbarch *gdbarch = get_frame_arch (frame);
struct type *type1 = check_typedef (type);
struct value *v;
if (gdbarch_convert_register_p (gdbarch, regnum, type1))
{
int optim, unavail, ok;
/* The ISA/ABI need to something weird when obtaining the
specified value from this register. It might need to
re-order non-adjacent, starting with REGNUM (see MIPS and
i386). It might need to convert the [float] register into
the corresponding [integer] type (see Alpha). The assumption
is that gdbarch_register_to_value populates the entire value
including the location. */
v = allocate_value (type);
VALUE_LVAL (v) = lval_register;
VALUE_FRAME_ID (v) = get_frame_id (frame);
VALUE_REGNUM (v) = regnum;
ok = gdbarch_register_to_value (gdbarch, frame, regnum, type1,
value_contents_raw (v), &optim,
&unavail);
if (!ok)
{
if (optim)
set_value_optimized_out (v, 1);
if (unavail)
mark_value_bytes_unavailable (v, 0, TYPE_LENGTH (type));
}
}
else
{
/* Construct the value. */
v = gdbarch_value_from_register (gdbarch, type, regnum, frame);
/* Get the data. */
read_frame_register_value (v, frame);
}
return v;
}
/* Return contents of register REGNUM in frame FRAME as address,
interpreted as value of type TYPE. Will abort if register
value is not available. */
CORE_ADDR
address_from_register (struct type *type, int regnum, struct frame_info *frame)
{
struct value *value;
CORE_ADDR result;
value = value_from_register (type, regnum, frame);
gdb_assert (value);
result = value_as_address (value);
release_value (value);
value_free (value);
return result;
}
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