[PATCH 12/43] Merge evaluate_for_locexpr_baton evaluator

Zoran Zaric via Gdb-patches
2021-03-01T14:47:00Z

From: Zoran Zaric <zoran.zaric@amd.com>

The evaluate_for_locexpr_baton is the last derived class from the
dwarf_expr_context class. It's purpose is to support the passed in
buffer functionality.

Although, it is not really necessary to merge this class with it's
base class, doing that simplifies new expression evaluator design.

Considering that this functionality is going around the DWARF standard,
it is also reasonable to expect that with a new evaluator design and
extending the push object address functionality to accept any location
description, there will be no need to support passed in buffers.

Alternatively, it would also makes sense to abstract the interaction
between the evaluator and a given resource in the near future. The
passed in buffer would then be a specialization of that abstraction.

gdb/ChangeLog:

* dwarf2/expr.c (dwarf_expr_context::read_mem): Merge with
evaluate_for_locexpr_baton implementation.
* dwarf2/loc.c (class evaluate_for_locexpr_baton): Remove
class.
(evaluate_for_locexpr_baton::read_mem): Move to
dwarf_expr_context.
(dwarf2_locexpr_baton_eval): Instantiate dwarf_expr_context
instead of evaluate_for_locexpr_baton class.
---
gdb/dwarf2/expr.c | 19 +++++++++++++++++--
gdb/dwarf2/expr.h | 13 +++----------
gdb/dwarf2/loc.c | 45 ++-------------------------------------------
3 files changed, 22 insertions(+), 55 deletions(-)

diff --git a/gdb/dwarf2/expr.c b/gdb/dwarf2/expr.c
index 1212be9c984..fe6d072ac8f 100644
--- a/gdb/dwarf2/expr.c
+++ b/gdb/dwarf2/expr.c
@@ -252,6 +252,18 @@ void
dwarf_expr_context::read_mem (gdb_byte *buf, CORE_ADDR addr,
size_t length)
{
+ if (length == 0)
+ return;
+
+ /* Prefer the passed-in memory, if it exists. */
+ CORE_ADDR offset = addr - obj_address;
+
+ if (offset < data_view.size () && offset + length <= data_view.size ())
+ {
+ memcpy (buf, data_view.data (), length);
+ return;
+ }
+
read_memory (addr, buf, length);
}

@@ -1576,8 +1588,11 @@ dwarf_expr_context::execute_stack_op (const gdb_byte *op_ptr,

case DW_OP_push_object_address:
/* Return the address of the object we are currently observing. */
- result = this->get_object_address ();
- result_val = value_from_ulongest (address_type, result);
+ if (this->data_view.data () == nullptr
+ && this->obj_address == 0)
+ error (_("Location address is not set."));
+
+ result_val = value_from_ulongest (address_type, this->obj_address);
break;

default:
diff --git a/gdb/dwarf2/expr.h b/gdb/dwarf2/expr.h
index 3faedebfb83..af14f6ee0c2 100644
--- a/gdb/dwarf2/expr.h
+++ b/gdb/dwarf2/expr.h
@@ -195,16 +195,8 @@ struct dwarf_expr_context
/* Object address used for the evaluation. */
CORE_ADDR obj_address = 0;

- /* Read LENGTH bytes at ADDR into BUF. */
- virtual void read_mem (gdb_byte *buf, CORE_ADDR addr, size_t length);
-
- /* Return the `object address' for DW_OP_push_object_address. */
- virtual CORE_ADDR get_object_address ()
- {
- if (obj_address == 0)
- error (_("Location address is not set."));
- return obj_address;
- }
+ /* The data that was passed in. */
+ gdb::array_view<const gdb_byte> data_view;

private:

@@ -239,6 +231,7 @@ struct dwarf_expr_context
void push_dwarf_reg_entry_value (enum call_site_parameter_kind kind,
union call_site_parameter_u kind_u,
int deref_size);
+ void read_mem (gdb_byte *buf, CORE_ADDR addr, size_t length);
};

/* Return the value of register number REG (a DWARF register number),
diff --git a/gdb/dwarf2/loc.c b/gdb/dwarf2/loc.c
index bd3f7d4d46a..d02fb1cd792 100644
--- a/gdb/dwarf2/loc.c
+++ b/gdb/dwarf2/loc.c
@@ -2221,45 +2221,6 @@ dwarf2_evaluate_loc_desc (struct type *type, struct frame_info *frame,
per_objfile, NULL, 0);
}

-/* A specialization of dwarf_expr_context that is used by
- dwarf2_locexpr_baton_eval. This subclass exists to handle the case
- where a caller of dwarf2_locexpr_baton_eval passes in some data,
- but with the address being 0. In this situation, we arrange for
- memory reads to come from the passed-in buffer. */
-
-struct evaluate_for_locexpr_baton : public dwarf_expr_context
-{
- evaluate_for_locexpr_baton (dwarf2_per_objfile *per_objfile)
- : dwarf_expr_context (per_objfile)
- {}
-
- /* The data that was passed in. */
- gdb::array_view<const gdb_byte> data_view;
-
- CORE_ADDR get_object_address () override
- {
- if (data_view.data () == nullptr && obj_address == 0)
- error (_("Location address is not set."));
- return obj_address;
- }
-
- void read_mem (gdb_byte *buf, CORE_ADDR addr, size_t len) override
- {
- if (len == 0)
- return;
-
- /* Prefer the passed-in memory, if it exists. */
- CORE_ADDR offset = addr - obj_address;
- if (offset < data_view.size () && offset + len <= data_view.size ())
- {
- memcpy (buf, data_view.data (), len);
- return;
- }
-
- read_memory (addr, buf, len);
- }
-};
-
/* Evaluates a dwarf expression and stores the result in VAL,
expecting that the dwarf expression only produces a single
CORE_ADDR. FRAME is the frame in which the expression is
@@ -2283,13 +2244,11 @@ dwarf2_locexpr_baton_eval (const struct dwarf2_locexpr_baton *dlbaton,
return 0;

dwarf2_per_objfile *per_objfile = dlbaton->per_objfile;
- evaluate_for_locexpr_baton ctx (per_objfile);
+ dwarf_expr_context ctx (per_objfile);

ctx.frame = frame;
ctx.per_cu = dlbaton->per_cu;
- if (addr_stack == nullptr)
- ctx.obj_address = 0;
- else
+ if (addr_stack != nullptr)
{
ctx.obj_address = addr_stack->addr;
ctx.data_view = addr_stack->valaddr;
--
2.17.1