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Commit 23323938 authored by Tom Tromey's avatar Tom Tromey
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Simplify decode_locdesc 

While looking into another bug, I noticed that the DWARF cooked
indexer picks up an address for this symbol:

 <1><82>: Abbrev Number: 2 (DW_TAG_variable)
    <83>   DW_AT_specification: <0x9f>
    <87>   DW_AT_location    : 10 byte block: e 0 0 0 0 0 0 0 0 e0 	(DW_OP_const8u: 0 0; DW_OP_GNU_push_tls_address or DW_OP_HP_unknown)
    <92>   DW_AT_linkage_name: (indirect string, offset: 0x156): _ZN9container8tlsvar_0E

This happens because decode_locdesc allows the use of
DW_OP_GNU_push_tls_address.

This didn't make sense to me.  I looked into it a bit more, and I
think decode_locdesc is used in three ways:

1. Find a constant address of a symbol that happens to be encoded as a
   location expression.

2. Find the offset of a function in a virtual table.  (This one should
   probably be replaced by code to just evaluate the expression in
   gnu-v3-abi.c -- but there's no point yet because no compiler
   actually seems to emit correct DWARF here, see the bug linked in
   the patch.)

3. Find the offset of a field, if the offset is a constant.

None of these require TLS.

This patch simplifies decode_locdesc by removing any opcodes that
don't fit into the above.  It also changes the API a little, to make
it less difficult to use.

Regression tested on x86-64 Fedora 36.
parent 02601231
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with 66 additions and 137 deletions
gdb/dwarf2/read.c
+ 66
− 137
View file @ 23323938
......@@ -942,8 +942,8 @@ static const char *namespace_name (struct die_info *die,
 
static void process_enumeration_scope (struct die_info *, struct dwarf2_cu *);
 
static CORE_ADDR decode_locdesc (struct dwarf_block *, struct dwarf2_cu *,
bool * = nullptr);
static bool decode_locdesc (struct dwarf_block *, struct dwarf2_cu *,
CORE_ADDR *addr);
 
static enum dwarf_array_dim_ordering read_array_order (struct die_info *,
struct dwarf2_cu *);
......@@ -11457,6 +11457,7 @@ handle_member_location (struct die_info *die, struct dwarf2_cu *cu,
if (attr != NULL)
{
*offset = 0;
CORE_ADDR temp;
 
/* Note that we do not check for a section offset first here.
This is because DW_AT_data_member_location is new in DWARF 4,
......@@ -11466,8 +11467,11 @@ handle_member_location (struct die_info *die, struct dwarf2_cu *cu,
*offset = attr->constant_value (0);
else if (attr->form_is_section_offset ())
dwarf2_complex_location_expr_complaint ();
else if (attr->form_is_block ())
*offset = decode_locdesc (attr->as_block (), cu);
else if (attr->form_is_block ()
&& decode_locdesc (attr->as_block (), cu, &temp))
{
*offset = temp;
}
else
dwarf2_complex_location_expr_complaint ();
 
......@@ -11520,9 +11524,8 @@ handle_member_location (struct die_info *die, struct dwarf2_cu *cu,
dwarf2_complex_location_expr_complaint ();
else if (attr->form_is_block ())
{
bool handled;
CORE_ADDR offset = decode_locdesc (attr->as_block (), cu, &handled);
if (handled)
CORE_ADDR offset;
if (decode_locdesc (attr->as_block (), cu, &offset))
field->set_loc_bitpos (offset * bits_per_byte);
else
{
......@@ -12242,18 +12245,25 @@ dwarf2_add_member_fn (struct field_info *fip, struct die_info *die,
if (attr->form_is_block () && attr->as_block ()->size > 0)
{
struct dwarf_block *block = attr->as_block ();
CORE_ADDR offset;
 
if (block->data[0] == DW_OP_constu)
if (block->data[0] == DW_OP_constu
&& decode_locdesc (block, cu, &offset))
{
/* Old-style GCC. */
fnp->voffset = decode_locdesc (block, cu) + 2;
/* "Old"-style GCC. See
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=44126
for discussion. This was known and a patch available
in 2010, but as of 2023, both GCC and clang still
emit this. */
fnp->voffset = offset + 2;
}
else if (block->data[0] == DW_OP_deref
|| (block->size > 1
&& block->data[0] == DW_OP_deref_size
&& block->data[1] == cu->header.addr_size))
else if ((block->data[0] == DW_OP_deref
|| (block->size > 1
&& block->data[0] == DW_OP_deref_size
&& block->data[1] == cu->header.addr_size))
&& decode_locdesc (block, cu, &offset))
{
fnp->voffset = decode_locdesc (block, cu);
fnp->voffset = offset;
if ((fnp->voffset % cu->header.addr_size) != 0)
dwarf2_complex_location_expr_complaint ();
else
......@@ -16226,9 +16236,10 @@ cooked_indexer::scan_attributes (dwarf2_per_cu_data *scanning_per_cu,
if (!scanning_per_cu->addresses_seen && attr.form_is_block ())
{
struct dwarf_block *locdesc = attr.as_block ();
CORE_ADDR addr = decode_locdesc (locdesc, reader->cu);
if (addr != 0
|| reader->cu->per_objfile->per_bfd->has_section_at_zero)
CORE_ADDR addr;
if (decode_locdesc (locdesc, reader->cu, &addr)
&& (addr != 0
|| reader->cu->per_objfile->per_bfd->has_section_at_zero))
{
low_pc = addr;
/* For variables, we don't want to try decoding the
......@@ -20926,14 +20937,34 @@ read_signatured_type (signatured_type *sig_type,
}
 
/* Decode simple location descriptions.
Given a pointer to a dwarf block that defines a location, compute
the location and return the value. If COMPUTED is non-null, it is
set to true to indicate that decoding was successful, and false
otherwise. If COMPUTED is null, then this function may emit a
complaint. */
 
static CORE_ADDR
decode_locdesc (struct dwarf_block *blk, struct dwarf2_cu *cu, bool *computed)
Given a pointer to a DWARF block that defines a location, compute
the location. Returns true if the expression was computable by
this function, false otherwise. On a true return, *RESULT is set.
Note that this function does not implement a full DWARF expression
evaluator. Instead, it is used for a few limited purposes:
- Getting the address of a symbol that has a constant address. For
example, if a symbol has a location like "DW_OP_addr", the address
can be extracted.
- Getting the offset of a virtual function in its vtable. There
are two forms of this, one of which involves DW_OP_deref -- so this
function handles derefs in a peculiar way to make this 'work'.
(Probably this area should be rewritten.)
- Getting the offset of a field, when it is constant.
Opcodes that cannot be part of a constant expression, for example
those involving registers, simply result in a return of
'false'.
This function may emit a complaint. */
static bool
decode_locdesc (struct dwarf_block *blk, struct dwarf2_cu *cu,
CORE_ADDR *result)
{
struct objfile *objfile = cu->per_objfile->objfile;
size_t i;
......@@ -20941,12 +20972,10 @@ decode_locdesc (struct dwarf_block *blk, struct dwarf2_cu *cu, bool *computed)
const gdb_byte *data = blk->data;
CORE_ADDR stack[64];
int stacki;
unsigned int bytes_read, unsnd;
unsigned int bytes_read;
gdb_byte op;
 
if (computed != nullptr)
*computed = false;
*result = 0;
i = 0;
stacki = 0;
stack[stacki] = 0;
......@@ -20992,61 +21021,6 @@ decode_locdesc (struct dwarf_block *blk, struct dwarf2_cu *cu, bool *computed)
stack[++stacki] = op - DW_OP_lit0;
break;
 
case DW_OP_reg0:
case DW_OP_reg1:
case DW_OP_reg2:
case DW_OP_reg3:
case DW_OP_reg4:
case DW_OP_reg5:
case DW_OP_reg6:
case DW_OP_reg7:
case DW_OP_reg8:
case DW_OP_reg9:
case DW_OP_reg10:
case DW_OP_reg11:
case DW_OP_reg12:
case DW_OP_reg13:
case DW_OP_reg14:
case DW_OP_reg15:
case DW_OP_reg16:
case DW_OP_reg17:
case DW_OP_reg18:
case DW_OP_reg19:
case DW_OP_reg20:
case DW_OP_reg21:
case DW_OP_reg22:
case DW_OP_reg23:
case DW_OP_reg24:
case DW_OP_reg25:
case DW_OP_reg26:
case DW_OP_reg27:
case DW_OP_reg28:
case DW_OP_reg29:
case DW_OP_reg30:
case DW_OP_reg31:
stack[++stacki] = op - DW_OP_reg0;
if (i < size)
{
if (computed == nullptr)
dwarf2_complex_location_expr_complaint ();
else
return 0;
}
break;
case DW_OP_regx:
unsnd = read_unsigned_leb128 (NULL, (data + i), &bytes_read);
i += bytes_read;
stack[++stacki] = unsnd;
if (i < size)
{
if (computed == nullptr)
dwarf2_complex_location_expr_complaint ();
else
return 0;
}
break;
case DW_OP_addr:
stack[++stacki] = cu->header.read_address (objfile->obfd.get (),
&data[i],
......@@ -21127,37 +21101,7 @@ decode_locdesc (struct dwarf_block *blk, struct dwarf2_cu *cu, bool *computed)
global symbols, although the variable's address will be bogus
in the psymtab. */
if (i < size)
{
if (computed == nullptr)
dwarf2_complex_location_expr_complaint ();
else
return 0;
}
break;
case DW_OP_GNU_push_tls_address:
case DW_OP_form_tls_address:
/* The top of the stack has the offset from the beginning
of the thread control block at which the variable is located. */
/* Nothing should follow this operator, so the top of stack would
be returned. */
/* This is valid for partial global symbols, but the variable's
address will be bogus in the psymtab. Make it always at least
non-zero to not look as a variable garbage collected by linker
which have DW_OP_addr 0. */
if (i < size)
{
if (computed == nullptr)
dwarf2_complex_location_expr_complaint ();
else
return 0;
}
stack[stacki]++;
break;
case DW_OP_GNU_uninit:
if (computed != nullptr)
return 0;
return false;
break;
 
case DW_OP_addrx:
......@@ -21169,41 +21113,26 @@ decode_locdesc (struct dwarf_block *blk, struct dwarf2_cu *cu, bool *computed)
break;
 
default:
if (computed == nullptr)
{
const char *name = get_DW_OP_name (op);
if (name)
complaint (_("unsupported stack op: '%s'"),
name);
else
complaint (_("unsupported stack op: '%02x'"),
op);
}
return (stack[stacki]);
return false;
}
 
/* Enforce maximum stack depth of SIZE-1 to avoid writing
outside of the allocated space. Also enforce minimum>0. */
if (stacki >= ARRAY_SIZE (stack) - 1)
{
if (computed == nullptr)
complaint (_("location description stack overflow"));
return 0;
complaint (_("location description stack overflow"));
return false;
}
 
if (stacki <= 0)
{
if (computed == nullptr)
complaint (_("location description stack underflow"));
return 0;
complaint (_("location description stack underflow"));
return false;
}
}
 
if (computed != nullptr)
*computed = true;
return (stack[stacki]);
*result = stack[stacki];
return true;
}
 
/* memory allocation interface */
......
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