From: Zoran Zaric <Zoran.Zaric@amd.com>
To: gdb-patches@sourceware.org
Cc: Zoran Zaric <Zoran.Zaric@amd.com>
Subject: [PATCH 18/30] Add new classes that model DWARF stack element
Date: Mon, 7 Dec 2020 19:00:19 +0000 [thread overview]
Message-ID: <20201207190031.13341-19-Zoran.Zaric@amd.com> (raw)
In-Reply-To: <20201207190031.13341-1-Zoran.Zaric@amd.com>
The rest of the patch series addresses the issues described in a
"Motivation" section of the AMD’s DWARF standard extensions that
can be found at:
https://llvm.org/docs/AMDGPUDwarfExtensionsForHeterogeneousDebugging.html
The document describes a couple of main issues found when using the
current DWARF 5 version to describe optimized code for SIMD and SIMT
architectures.
Without going much into details described in the document, the main
point is that DWARF version 5 does not allow a proper support for
address spaces and it does not allow a location description to be part
of a DWARF expression, unless it is a leaf node of that expression.
Both issues can be solved in a clean way by introducing a new set of
classes that describe all entry types which can be placed on a DWARF
stack, while keeping a full backward compatibility with the previous
standard version. These entry types can now be either a typed value
or any location description.
Currently, the result of an expression evaluation is kept in a separate
data structure, while with the new approach, it will be always found as
a top element of the DWARF stack. The reason why this approach is
backward compatible is because in version 5, a location description
is only allowed to be a leaf node of the expression or a composite
piece.
Question here is, why do we need a new set of classes and why not just
use the struct value instead?
As it stands, there are couple of issues with using the struct value to
describe a DWARF stack element:
- It is not designed to represent a DWARF location description
specifically, instead it behaves more like unified debug information
format that represents an actual target resource. One example of this
is accessing data of a struct value register location description,
where if the amount of data accessed is larger then the register,
results in accessing more then one register. In DWARF this is not a
valid behavior and locations that span more then one register should be
described as a composite location description.
- There is a tight coupling between struct value and it’s type
information, regardless if the data represented is describing a value
(not_lval) or a location description. While the type information
dictates how the data is accessed for a struct value case, in DWARF,
location description doesn’t have a type so data access is not bound by
it.
- DWARF values only support much simpler base types, while struct value
can be linked to any type. Admittedly, new classes are still using the
same struct value infrastructure for a value based operations at the
moment, but that is planned to change in the near future.
- struct value register location description requires a frame id
information which makes them unsuitable for CFA expression evaluation.
So, there seems to be a lack of separation of concerns in the design
of a struct value infrastructure, while the new classes are handling
one specific purpose and are completely encapsulated in the expr.c.
Additional benefit of this design is that it makes a step in a
right direction for being able to evaluate DWARF expressions on a
gdbserver side in the near future, which sounds like a desirable thing.
It is also worth mentioning that this new location description
representation is based on a bit granularity (the bit_suboffset class
member) even though the DWARF standard has a very limited support for
it (mostly used for DW_OP_bit_piece operation).
By allowing any location description to define a bit sub-offset of the
location, we are able to give more options for supporting of new
concepts (like the existing packed arrays in Ada language).
In this patch, a new set of classes that describe a DWARF stack element
are added. The new classes are:
- Value - describes a numerical value with a DWARF base type.
- Location description - describes a DWARF location description.
- Undefined location - describes a location that is not defined.
- Memory location - describes a location in memory.
- Register location - describes a register location in a frame
context.
- Implicit location - describes a location that implicitly holds a
value that it describes.
- Implicit pointer - describes a concept of an implicit pointer to
a source variable.
- Composite location - describes a location that is composed from
pieces of other location descriptions.
For now, these classes are just defined, and they are planned to be
used by the following patches.
gdb/ChangeLog:
* dwarf2/expr.c (class dwarf_entry): New class.
(class dwarf_value): New class.
(class dwarf_location): New class.
(class dwarf_undefined): New class.
(class dwarf_memory): New class.
(class dwarf_register): New class.
(class dwarf_implicit): New class.
(class dwarf_implicit_pointer): New class.
(class dwarf_composite): New class.
* value.c (pack_unsigned_long): Expose function.
* value.h (pack_unsigned_long): Expose function.
---
gdb/dwarf2/expr.c | 346 ++++++++++++++++++++++++++++++++++++++++++++++
gdb/value.c | 2 +-
gdb/value.h | 2 +
3 files changed, 349 insertions(+), 1 deletion(-)
diff --git a/gdb/dwarf2/expr.c b/gdb/dwarf2/expr.c
index 0c9ea51e5b..c0bb06fc4c 100644
--- a/gdb/dwarf2/expr.c
+++ b/gdb/dwarf2/expr.c
@@ -267,6 +267,352 @@ write_to_memory (CORE_ADDR address, const gdb_byte *buffer,
length, buffer);
}
+/* Base class that describes entries found on a DWARF expression
+ evaluation stack. */
+
+class dwarf_entry : public refcounted_object
+{
+public:
+ /* Not expected to be called on it's own. */
+ dwarf_entry () = default;
+
+ virtual ~dwarf_entry () = 0;
+};
+
+dwarf_entry::~dwarf_entry () = default;
+
+/* Value entry found on a DWARF expression evaluation stack. */
+
+class dwarf_value : public dwarf_entry
+{
+public:
+ dwarf_value (const gdb_byte* contents, struct type *type)
+ {
+ size_t type_len = TYPE_LENGTH (type);
+ m_contents.reset ((gdb_byte *) xzalloc (type_len));
+
+ memcpy (m_contents.get (), contents, type_len);
+ m_type = type;
+ }
+
+ dwarf_value (ULONGEST value, struct type *type)
+ {
+ m_contents.reset ((gdb_byte *) xzalloc (TYPE_LENGTH (type)));
+
+ pack_unsigned_long (m_contents.get (), type, value);
+ m_type = type;
+ }
+
+ dwarf_value (LONGEST value, struct type *type)
+ {
+ m_contents.reset ((gdb_byte *) xzalloc (TYPE_LENGTH (type)));
+
+ pack_long (m_contents.get (), type, value);
+ m_type = type;
+ }
+
+ virtual ~dwarf_value () = default;
+
+ const gdb_byte* get_contents () const
+ {
+ return m_contents.get ();
+ }
+
+ struct type* get_type () const
+ {
+ return m_type;
+ }
+
+ LONGEST to_long () const
+ {
+ return unpack_long (m_type, m_contents.get ());
+ }
+
+private:
+ /* Value contents as a stream of bytes in target byte order. */
+ gdb::unique_xmalloc_ptr<gdb_byte> m_contents;
+
+ /* Type of the value held by the entry. */
+ struct type *m_type;
+};
+
+/* Location description entry found on a DWARF expression evaluation stack.
+
+ Types of locations descirbed can be: register location, memory location,
+ implicit location, implicit pointer location, undefined location and
+ composite location (made out of any of the location types including
+ another composite location). */
+
+class dwarf_location : public dwarf_entry
+{
+public:
+ /* Not expected to be called on it's own. */
+ dwarf_location (LONGEST offset = 0, LONGEST bit_suboffset = 0)
+ : m_initialised (true)
+ {
+ m_offset = offset;
+ m_offset += bit_suboffset / HOST_CHAR_BIT;
+ m_bit_suboffset = bit_suboffset % HOST_CHAR_BIT;
+ }
+
+ virtual ~dwarf_location () = default;
+
+ LONGEST get_offset () const
+ {
+ return m_offset;
+ };
+
+ LONGEST get_bit_suboffset () const
+ {
+ return m_bit_suboffset;
+ };
+
+ void add_bit_offset (LONGEST bit_offset)
+ {
+ LONGEST bit_total_offset = m_bit_suboffset + bit_offset;
+
+ m_offset += bit_total_offset / HOST_CHAR_BIT;
+ m_bit_suboffset = bit_total_offset % HOST_CHAR_BIT;
+ };
+
+ void set_initialised (bool initialised)
+ {
+ m_initialised = initialised;
+ };
+
+ bool is_initialised () const
+ {
+ return m_initialised;
+ };
+
+private:
+ /* Byte offset into the location. */
+ LONGEST m_offset;
+
+ /* Bit suboffset of the last byte. */
+ LONGEST m_bit_suboffset;
+
+ /* Whether the location is initialized. Used for non-standard
+ DW_OP_GNU_uninit operation. */
+ bool m_initialised;
+};
+
+/* Undefined location description entry. This is a special location
+ description type that describes the location description that is
+ not known. */
+
+class dwarf_undefined : public dwarf_location
+{
+public:
+ dwarf_undefined (LONGEST offset = 0, LONGEST bit_suboffset = 0)
+ : dwarf_location (offset, bit_suboffset)
+ {}
+};
+
+class dwarf_memory : public dwarf_location
+{
+public:
+ dwarf_memory (LONGEST offset, LONGEST bit_suboffset = 0,
+ bool stack = false)
+ : dwarf_location (offset, bit_suboffset),
+ m_stack (stack)
+ {}
+
+ bool in_stack () const
+ {
+ return m_stack;
+ };
+
+ void set_stack (bool stack)
+ {
+ m_stack = stack;
+ };
+private:
+ /* True if the location belongs to a stack memory region. */
+ bool m_stack;
+};
+
+/* Register location description entry. */
+
+class dwarf_register : public dwarf_location
+{
+public:
+ dwarf_register (unsigned int regnum,
+ LONGEST offset = 0, LONGEST bit_suboffset = 0)
+ : dwarf_location (offset, bit_suboffset),
+ m_regnum (regnum)
+ {}
+
+ unsigned int get_regnum () const
+ {
+ return m_regnum;
+ };
+
+private:
+ /* DWARF register number. */
+ unsigned int m_regnum;
+};
+
+/* Implicit location description entry. Describes a location
+ description not found on the target but instead saved in a
+ gdb-allocated buffer. */
+
+class dwarf_implicit : public dwarf_location
+{
+public:
+
+ dwarf_implicit (const gdb_byte* contents, size_t size,
+ enum bfd_endian byte_order)
+ {
+ m_contents.reset ((gdb_byte *) xzalloc (size));
+
+ memcpy (m_contents.get (), contents, size);
+ m_size = size;
+ m_byte_order = byte_order;
+ }
+
+ const gdb_byte* get_contents () const
+ {
+ return m_contents.get ();
+ }
+
+ size_t get_size () const
+ {
+ return m_size;
+ }
+
+ size_t get_byte_order () const
+ {
+ return m_byte_order;
+ }
+
+private:
+ /* Implicit location contents as a stream of bytes in target byte-order. */
+ gdb::unique_xmalloc_ptr<gdb_byte> m_contents;
+
+ /* Contents byte stream size. */
+ size_t m_size;
+
+ /* Contents original byte order. */
+ enum bfd_endian m_byte_order;
+};
+
+/* Implicit pointer location description entry. */
+
+class dwarf_implicit_pointer : public dwarf_location
+{
+public:
+ dwarf_implicit_pointer (dwarf2_per_objfile *per_objfile,
+ struct dwarf2_per_cu_data *per_cu,
+ int addr_size, sect_offset die_offset,
+ LONGEST offset, LONGEST bit_suboffset = 0)
+ : dwarf_location (offset, bit_suboffset),
+ m_per_objfile (per_objfile), m_per_cu (per_cu),
+ m_addr_size (addr_size), m_die_offset (die_offset)
+ {}
+
+ dwarf2_per_objfile *get_per_objfile () const
+ {
+ return m_per_objfile;
+ }
+
+ dwarf2_per_cu_data *get_per_cu () const
+ {
+ return m_per_cu;
+ }
+
+ int get_addr_size () const
+ {
+ return m_addr_size;
+ }
+
+ sect_offset get_die_offset () const
+ {
+ return m_die_offset;
+ }
+
+private:
+ /* Per object file data of the implicit pointer. */
+ dwarf2_per_objfile *m_per_objfile;
+
+ /* Compilation unit context of the implicit pointer. */
+ struct dwarf2_per_cu_data *m_per_cu;
+
+ /* Address size for the evaluation. */
+ int m_addr_size;
+
+ /* DWARF die offset pointed by the implicit pointer. */
+ sect_offset m_die_offset;
+};
+
+/* Composite location description entry. */
+
+class dwarf_composite : public dwarf_location
+{
+public:
+ dwarf_composite (LONGEST offset = 0, LONGEST bit_suboffset = 0)
+ : dwarf_location (offset, bit_suboffset)
+ {}
+
+ /* A composite location gets detached from its factory object for
+ the purpose of lval_computed resolution, which means that it
+ needs to take care of garbage collecting its pieces. */
+ ~dwarf_composite () override
+ {
+ for (unsigned int i = 0; i < m_pieces.size (); i++)
+ {
+ dwarf_location* location = m_pieces[i].m_location;
+
+ location->decref ();
+
+ if (location->refcount () == 0)
+ delete location;
+ }
+ }
+
+ void add_piece (dwarf_location* location, ULONGEST bit_size)
+ {
+ gdb_assert (location != nullptr);
+ location->incref ();
+ m_pieces.emplace_back (location, bit_size);
+ }
+
+ const dwarf_location* get_piece_at (unsigned int index) const
+ {
+ gdb_assert (index < m_pieces.size ());
+ return m_pieces[index].m_location;
+ }
+
+ ULONGEST get_bit_size_at (unsigned int index) const
+ {
+ gdb_assert (index < m_pieces.size ());
+ return m_pieces[index].m_size;
+ }
+
+ size_t get_pieces_num () const
+ {
+ return m_pieces.size ();
+ }
+
+private:
+ /* Composite piece that contains a piece location
+ description and it's size. */
+ class piece
+ {
+ public:
+ piece (dwarf_location *location, ULONGEST size)
+ : m_location (location),
+ m_size (size)
+ {}
+
+ dwarf_location *m_location;
+ ULONGEST m_size;
+ };
+
+ /* Vector of composite pieces. */
+ std::vector<struct piece> m_pieces;
+};
+
struct piece_closure
{
/* Reference count. */
diff --git a/gdb/value.c b/gdb/value.c
index eba5bce6d2..5f52c2d566 100644
--- a/gdb/value.c
+++ b/gdb/value.c
@@ -3401,7 +3401,7 @@ pack_long (gdb_byte *buf, struct type *type, LONGEST num)
/* Pack NUM into BUF using a target format of TYPE. */
-static void
+void
pack_unsigned_long (gdb_byte *buf, struct type *type, ULONGEST num)
{
LONGEST len;
diff --git a/gdb/value.h b/gdb/value.h
index d026c8ed95..2eaba57487 100644
--- a/gdb/value.h
+++ b/gdb/value.h
@@ -677,6 +677,8 @@ extern struct value *value_field_bitfield (struct type *type, int fieldno,
const struct value *val);
extern void pack_long (gdb_byte *buf, struct type *type, LONGEST num);
+extern void pack_unsigned_long (gdb_byte *buf, struct type *type,
+ ULONGEST num);
extern struct value *value_from_longest (struct type *type, LONGEST num);
extern struct value *value_from_ulongest (struct type *type, ULONGEST num);
--
2.17.1
next prev parent reply other threads:[~2020-12-07 19:01 UTC|newest]
Thread overview: 75+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-07 19:00 [PATCH 00/30] Allow location description on the DWARF stack Zoran Zaric
2020-12-07 19:00 ` [PATCH 01/30] Replace the symbol needs evaluator with a parser Zoran Zaric
2021-01-21 21:16 ` Tom Tromey
2021-01-21 21:48 ` Zoran Zaric
2021-02-23 14:15 ` Zoran Zaric
2020-12-07 19:00 ` [PATCH 02/30] Move frame context info to dwarf_expr_context Zoran Zaric
2021-01-21 21:23 ` Tom Tromey
2020-12-07 19:00 ` [PATCH 03/30] Remove get_frame_cfa from dwarf_expr_context Zoran Zaric
2021-01-21 21:23 ` Tom Tromey
2020-12-07 19:00 ` [PATCH 04/30] Move compilation unit info to dwarf_expr_context Zoran Zaric
2021-01-21 21:28 ` Tom Tromey
2021-02-23 14:21 ` Zoran Zaric
2020-12-07 19:00 ` [PATCH 05/30] Move dwarf_call " Zoran Zaric
2021-01-21 21:30 ` Tom Tromey
2020-12-07 19:00 ` [PATCH 06/30] Move get_object_address " Zoran Zaric
2021-01-21 21:31 ` Tom Tromey
2021-02-23 14:33 ` Zoran Zaric
2020-12-07 19:00 ` [PATCH 07/30] Move read_mem " Zoran Zaric
2021-01-21 21:34 ` Tom Tromey
2020-12-07 19:00 ` [PATCH 08/30] Move push_dwarf_reg_entry_value to expr.c Zoran Zaric
2021-01-21 21:35 ` Tom Tromey
2020-12-07 19:00 ` [PATCH 09/30] Inline get_reg_value method of dwarf_expr_context Zoran Zaric
2021-01-21 21:36 ` Tom Tromey
2020-12-07 19:00 ` [PATCH 10/30] Remove empty frame and full evaluators Zoran Zaric
2021-01-21 21:37 ` Tom Tromey
2020-12-07 19:00 ` [PATCH 11/30] Merge evaluate_for_locexpr_baton evaluator Zoran Zaric
2021-02-08 21:21 ` Tom Tromey
2020-12-07 19:00 ` [PATCH 12/30] Move piece_closure and its support to expr.c Zoran Zaric
2021-02-08 21:32 ` Tom Tromey
2021-02-09 14:53 ` Zoran Zaric
2020-12-07 19:00 ` [PATCH 13/30] Make DWARF evaluator return a single struct value Zoran Zaric
2021-02-08 21:35 ` Tom Tromey
2021-02-09 14:55 ` Zoran Zaric
2021-02-09 17:13 ` Tom Tromey
2020-12-07 19:00 ` [PATCH 14/30] Simplify dwarf_expr_context class interface Zoran Zaric
2021-02-08 21:38 ` Tom Tromey
2021-02-09 14:56 ` Zoran Zaric
2021-02-23 14:38 ` Zoran Zaric
2020-12-07 19:00 ` [PATCH 15/30] Add as_lval argument to expression evaluator Zoran Zaric
2021-02-08 21:41 ` Tom Tromey
2021-02-09 15:25 ` Zoran Zaric
2021-02-09 20:33 ` Tom Tromey
2020-12-07 19:00 ` [PATCH 16/30] Add new register access interface to expr.c Zoran Zaric
2021-02-09 19:37 ` Tom Tromey
2020-12-07 19:00 ` [PATCH 17/30] Add new memory " Zoran Zaric
2021-02-09 19:45 ` Tom Tromey
2021-02-23 15:35 ` Zoran Zaric
2020-12-07 19:00 ` Zoran Zaric [this message]
2021-02-08 21:54 ` [PATCH 18/30] Add new classes that model DWARF stack element Tom Tromey
2021-02-09 17:34 ` Zoran Zaric
2021-02-09 20:36 ` Tom Tromey
2021-02-09 21:07 ` Tom Tromey
2021-02-09 21:26 ` Zoran Zaric
2021-02-23 14:57 ` Zoran Zaric
2020-12-07 19:00 ` [PATCH 19/30] Add new location description access interface Zoran Zaric
2021-02-08 21:46 ` Tom Tromey
2021-02-09 16:00 ` Zoran Zaric
2021-02-09 17:30 ` Zoran Zaric
2021-02-23 14:49 ` Zoran Zaric
2020-12-07 19:00 ` [PATCH 20/30] Add dwarf_entry factory class to expr.c Zoran Zaric
2021-02-09 19:54 ` Tom Tromey
2020-12-07 19:00 ` [PATCH 21/30] Change DWARF stack to use new dwarf_entry classes Zoran Zaric
2021-02-09 20:11 ` Tom Tromey
2020-12-07 19:00 ` [PATCH 22/30] Remove dwarf_expr_context from expr.h interface Zoran Zaric
2020-12-07 19:00 ` [PATCH 23/30] Rename and update the piece_closure structure Zoran Zaric
2020-12-07 19:00 ` [PATCH 24/30] Move read_addr_from_reg function to frame.c Zoran Zaric
2020-12-07 19:00 ` [PATCH 25/30] Add frame info check to DW_OP_reg operations Zoran Zaric
2020-12-07 19:00 ` [PATCH 26/30] Remove DWARF expression composition check Zoran Zaric
2020-12-07 19:00 ` [PATCH 27/30] Add support for any location description in CFI Zoran Zaric
2020-12-07 19:00 ` [PATCH 28/30] Add DWARF operations for byte and bit offset Zoran Zaric
2020-12-07 19:00 ` [PATCH 29/30] Add support for DW_OP_LLVM_undefined operation Zoran Zaric
2020-12-07 19:00 ` [PATCH 30/30] Add support for nested composite locations Zoran Zaric
2020-12-08 14:48 ` [PATCH 00/30] Allow location description on the DWARF stack Metzger, Markus T
2020-12-08 16:17 ` Simon Marchi
2020-12-09 0:30 ` Tye, Tony
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