[PATCH 17/43] Add as_lval argument to expression evaluator

Zoran Zaric via Gdb-patches
2021-03-01T14:47:14Z

There are cases where the result of the expression evaluation is
expected to be in a form of a value and not location description.

One place that has this requirement is dwarf_entry_parameter_to_value
function, but more are expected in the future. Until now, this
requirement was fulfilled by extending the evaluated expression with
a DW_OP_stack_value operation at the end.

New implementation, introduces a new evaluation argument instead.

* dwarf2/expr.c (dwarf_expr_context::fetch_result): Add as_lval
argument.
(dwarf_expr_context::eval_exp): Add as_lval argument.
* dwarf2/expr.h (struct dwarf_expr_context): Add as_lval
argument to fetch_result and eval_exp methods.
* dwarf2/frame.c (execute_stack_op): Add as_lval argument.
* dwarf2/loc.c (dwarf_entry_parameter_to_value): Remove
DWARF expression extension.
(dwarf2_evaluate_loc_desc_full): Add as_lval argument support.
(dwarf2_evaluate_loc_desc): Add as_lval argument support.
(dwarf2_locexpr_baton_eval): Add as_lval argument support.
---
gdb/dwarf2/expr.c | 12 +++++++++---
gdb/dwarf2/expr.h | 19 ++++++++++++-------
gdb/dwarf2/frame.c | 2 +-
gdb/dwarf2/loc.c | 27 ++++++++++-----------------
gdb/dwarf2/loc.h | 6 ++++--
5 files changed, 36 insertions(+), 30 deletions(-)

diff --git a/gdb/dwarf2/expr.c b/gdb/dwarf2/expr.c
index 1645f477d74..c50bb3c8d90 100644
--- a/gdb/dwarf2/expr.c
+++ b/gdb/dwarf2/expr.c
@@ -899,7 +899,8 @@ dwarf_expr_context::push_dwarf_reg_entry_value
struct value *
dwarf_expr_context::fetch_result (struct type *type,
struct type *subobj_type,
- LONGEST subobj_offset)
+ LONGEST subobj_offset,
+ bool as_lval)
{
struct value *retval = nullptr;

@@ -929,6 +930,11 @@ dwarf_expr_context::fetch_result (struct type *type,
}
else
{
+ /* If AS_LVAL is false, means that the implicit conversion
+ from a location description to value is expected. */
+ if (as_lval == false)
+ this->location = DWARF_VALUE_STACK;
+
switch (this->location)
{
case DWARF_VALUE_REGISTER:
@@ -1053,7 +1059,7 @@ dwarf_expr_context::fetch_result (struct type *type,
/* See expr.h. */

struct value *
-dwarf_expr_context::evaluate (const gdb_byte *addr, size_t len,
+dwarf_expr_context::evaluate (const gdb_byte *addr, size_t len, bool as_lval,
struct dwarf2_per_cu_data *per_cu,
struct frame_info *frame,
const struct property_addr_info *addr_info,
@@ -1069,7 +1075,7 @@ dwarf_expr_context::evaluate (const gdb_byte *addr, size_t len,
this->ref_addr_size = per_cu->ref_addr_size ();

eval (addr, len);
- return fetch_result (type, subobj_type, subobj_offset);
+ return fetch_result (type, subobj_type, subobj_offset, as_lval);
}

/* Require that TYPE be an integral type; throw an exception if not. */
diff --git a/gdb/dwarf2/expr.h b/gdb/dwarf2/expr.h
index d1374068732..3f519e81849 100644
--- a/gdb/dwarf2/expr.h
+++ b/gdb/dwarf2/expr.h
@@ -130,11 +130,13 @@ struct dwarf_expr_context
void push_address (CORE_ADDR value, bool in_stack_memory);

/* Evaluate the expression at ADDR (LEN bytes long) in a given PER_CU
- FRAME context. Where TYPE, SUBOBJ_TYPE and SUBOBJ_OFFSET describe
- expected struct value representation of the evaluation result.
- The ADDR_INFO property can be specified to override the range of
- memory addresses with the passed in buffer. */
- struct value *evaluate (const gdb_byte *addr, size_t len,
+ FRAME context. AS_LVAL defines if the returned struct value is
+ expected to be a value or a location description. Where TYPE,
+ SUBOBJ_TYPE and SUBOBJ_OFFSET describe expected struct value
+ representation of the evaluation result. The ADDR_INFO property
+ can be specified to override the range of memory addresses with
+ the passed in buffer. */
+ struct value *evaluate (const gdb_byte *addr, size_t len, bool as_lval,
struct dwarf2_per_cu_data *per_cu,
struct frame_info *frame,
const struct property_addr_info *addr_info = nullptr,
@@ -223,10 +225,13 @@ struct dwarf_expr_context

/* Fetch the result of the expression evaluation in a form of
a struct value, where TYPE, SUBOBJ_TYPE and SUBOBJ_OFFSET
- describe the source level representation of that result. */
+ describe the source level representation of that result.
+ AS_LVAL defines if the fetched struct value is expected to
+ be a value or a location description. */
struct value *fetch_result (struct type *type,
struct type *subobj_type,
- LONGEST subobj_offset);
+ LONGEST subobj_offset,
+ bool as_lval);

/* Return the location expression for the frame base attribute, in
START and LENGTH. The result must be live until the current
diff --git a/gdb/dwarf2/frame.c b/gdb/dwarf2/frame.c
index 07667c3dee5..51d308fd94f 100644
--- a/gdb/dwarf2/frame.c
+++ b/gdb/dwarf2/frame.c
@@ -232,7 +232,7 @@ execute_stack_op (const gdb_byte *exp, ULONGEST len, int addr_size,
scoped_value_mark free_values;

ctx.push_address (initial, initial_in_stack_memory);
- struct value *result_val = ctx.evaluate (exp, len, nullptr, this_frame);
+ struct value *result_val = ctx.evaluate (exp, len, true, nullptr, this_frame);

if (VALUE_LVAL (result_val) == lval_memory)
return value_address (result_val);
diff --git a/gdb/dwarf2/loc.c b/gdb/dwarf2/loc.c
index 55445021ad4..c53413a942f 100644
--- a/gdb/dwarf2/loc.c
+++ b/gdb/dwarf2/loc.c
@@ -50,7 +50,7 @@
static struct value *dwarf2_evaluate_loc_desc_full
(struct type *type, struct frame_info *frame, const gdb_byte *data,
size_t size, dwarf2_per_cu_data *per_cu, dwarf2_per_objfile *per_objfile,
- struct type *subobj_type, LONGEST subobj_byte_offset);
+ struct type *subobj_type, LONGEST subobj_byte_offset, bool as_lval = true);

/* Until these have formal names, we define these here.
ref: http://gcc.gnu.org/wiki/DebugFission
@@ -1183,7 +1183,6 @@ dwarf_entry_parameter_to_value (struct call_site_parameter *parameter,
dwarf2_per_objfile *per_objfile)
{
const gdb_byte *data_src;
- gdb_byte *data;
size_t size;

data_src = deref_size == -1 ? parameter->value : parameter->data_value;
@@ -1194,15 +1193,8 @@ dwarf_entry_parameter_to_value (struct call_site_parameter *parameter,
throw_error (NO_ENTRY_VALUE_ERROR,
_("Cannot resolve DW_AT_call_data_value"));

- /* DW_AT_call_value is a DWARF expression, not a DWARF
- location. Postprocessing of DWARF_VALUE_MEMORY would lose the type from
- DWARF block. */
- data = (gdb_byte *) alloca (size + 1);
- memcpy (data, data_src, size);
- data[size] = DW_OP_stack_value;
-
- return dwarf2_evaluate_loc_desc (type, caller_frame, data, size + 1, per_cu,
- per_objfile);
+ return dwarf2_evaluate_loc_desc (type, caller_frame, data_src, size, per_cu,
+ per_objfile, false);
}

/* VALUE must be of type lval_computed with entry_data_value_funcs. Perform
@@ -1428,7 +1420,8 @@ dwarf2_evaluate_loc_desc_full (struct type *type, struct frame_info *frame,
dwarf2_per_cu_data *per_cu,
dwarf2_per_objfile *per_objfile,
struct type *subobj_type,
- LONGEST subobj_byte_offset)
+ LONGEST subobj_byte_offset,
+ bool as_lval)
{
if (subobj_type == NULL)
{
@@ -1448,8 +1441,8 @@ dwarf2_evaluate_loc_desc_full (struct type *type, struct frame_info *frame,

try
{
- retval = ctx.evaluate (data, size, per_cu, frame, nullptr, type,
- subobj_type, subobj_byte_offset);
+ retval = ctx.evaluate (data, size, as_lval, per_cu, frame, nullptr,
+ type, subobj_type, subobj_byte_offset);
}
catch (const gdb_exception_error &ex)
{
@@ -1490,10 +1483,10 @@ struct value *
dwarf2_evaluate_loc_desc (struct type *type, struct frame_info *frame,
const gdb_byte *data, size_t size,
dwarf2_per_cu_data *per_cu,
- dwarf2_per_objfile *per_objfile)
+ dwarf2_per_objfile *per_objfile, bool as_lval)
{
return dwarf2_evaluate_loc_desc_full (type, frame, data, size, per_cu,
- per_objfile, NULL, 0);
+ per_objfile, NULL, 0, as_lval);
}

/* Evaluates a dwarf expression and stores the result in VAL,
@@ -1536,7 +1529,7 @@ dwarf2_locexpr_baton_eval (const struct dwarf2_locexpr_baton *dlbaton,
try
{
result = ctx.evaluate (dlbaton->data, dlbaton->size,
- per_cu, frame, addr_stack);
+ true, per_cu, frame, addr_stack);
}
catch (const gdb_exception_error &ex)
{
diff --git a/gdb/dwarf2/loc.h b/gdb/dwarf2/loc.h
index 02c686e5592..c5cacce1ceb 100644
--- a/gdb/dwarf2/loc.h
+++ b/gdb/dwarf2/loc.h
@@ -69,14 +69,16 @@ struct call_site_parameter *dwarf_expr_reg_to_entry_parameter

/* Evaluate a location description, starting at DATA and with length
SIZE, to find the current location of variable of TYPE in the context
- of FRAME. */
+ of FRAME. AS_LVAL defines if the resulting struct value is expected to
+ be a value or a location description. */

struct value *dwarf2_evaluate_loc_desc (struct type *type,
struct frame_info *frame,
const gdb_byte *data,
size_t size,
dwarf2_per_cu_data *per_cu,
- dwarf2_per_objfile *per_objfile);
+ dwarf2_per_objfile *per_objfile,
+ bool as_lval = true);

/* A chain of addresses that might be needed to resolve a dynamic
property. */
--
2.17.1