[PATCH v4 31/44] gdb, dwarf, ze: add DW_OP_INTEL_regval_bits

Add support for a new DWARF expression proposed in
https://dwarfstd.org/ShowIssue.php?issue=201007.1.

Cc: <[email protected]>
---
 binutils/dwarf.c   |  6 ++++++
 gdb/dwarf2/expr.c  | 37 +++++++++++++++++++++++++++++++++++++
 gdb/dwarf2/expr.h  |  5 +++++
 gdb/dwarf2/loc.c   |  2 ++
 include/dwarf2.def |  4 ++++
 5 files changed, 54 insertions(+)

diff --git a/binutils/dwarf.c b/binutils/dwarf.c
index 829bcb761f7..bdeaf393572 100644
--- a/binutils/dwarf.c
+++ b/binutils/dwarf.c
@@ -1882,6 +1882,12 @@ decode_location_expression (unsigned char * data,
 	  printf ("DW_OP_PGI_omp_thread_num");
 	  break;
 
+	  /* Intel wide registers extension.  */
+	case DW_OP_INTEL_regval_bits:
+	  SAFE_BYTE_GET_AND_INC (uvalue, data, 1, end);
+	  printf ("DW_OP_INTEL_regval_bits: %lu", (unsigned long) uvalue);
+	  break;
+
 	default:
 	  if (op >= DW_OP_lo_user
 	      && op <= DW_OP_hi_user)
diff --git a/gdb/dwarf2/expr.c b/gdb/dwarf2/expr.c
index 3a6b8f58199..03dae5bb064 100644
--- a/gdb/dwarf2/expr.c
+++ b/gdb/dwarf2/expr.c
@@ -946,6 +946,29 @@ dwarf_expr_context::deref (CORE_ADDR addr, int size, struct type *type)
 
 /* See expr.h.  */
 
+void
+dwarf_expr_context::read_reg (gdb_byte *buf, size_t bitoffset,
+			      size_t bitsize, int dwregnum)
+{
+  struct gdbarch * const gdbarch = get_frame_arch (this->m_frame);
+  const int regnum = dwarf_reg_to_regnum_or_error (gdbarch, dwregnum);
+
+  const int regsize = register_size (gdbarch, regnum);
+  if ((regsize * 8) <  (bitsize + bitoffset))
+    error (_("DWARF expr: error accessing %s[%" PRIu64 ":%" PRIu64 "]"),
+	   gdbarch_register_name (gdbarch, regnum),
+	   bitsize + bitoffset - 1, bitoffset);
+
+  gdb_byte * const regbuf = (gdb_byte *) alloca (regsize);
+  get_frame_register (this->m_frame, regnum,
+		      gdb::make_array_view (regbuf, regsize));
+
+  const enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
+  copy_bitwise (buf, 0, regbuf, bitoffset, bitsize, byte_order);
+}
+
+/* See expr.h.  */
+
 void
 dwarf_expr_context::push_dwarf_reg_entry_value (call_site_parameter_kind kind,
 						call_site_parameter_u kind_u,
@@ -2459,6 +2482,20 @@ dwarf_expr_context::execute_stack_op (gdb::array_view<const gdb_byte> expr)
 	  }
 	  break;
 
+	case DW_OP_INTEL_regval_bits:
+	  {
+	    uint8_t size = *op_ptr++;
+	    const ULONGEST off = value_as_long (fetch (0));
+	    pop ();
+	    const LONGEST dwregnum = value_as_long (fetch (0));
+	    pop ();
+
+	    result = 0;
+	    read_reg ((gdb_byte *) &result, off, size, dwregnum);
+	    result_val = value_from_ulongest (address_type, result);
+	  }
+	  break;
+
 	case DW_OP_convert:
 	case DW_OP_GNU_convert:
 	case DW_OP_reinterpret:
diff --git a/gdb/dwarf2/expr.h b/gdb/dwarf2/expr.h
index 02b0e41f6fd..bc07ae4b95f 100644
--- a/gdb/dwarf2/expr.h
+++ b/gdb/dwarf2/expr.h
@@ -256,6 +256,11 @@ struct dwarf_expr_context
      memory reads to come from the passed-in buffer.  */
   void read_mem (gdb_byte *buf, CORE_ADDR addr, size_t length);
 
+  /* Read BITSIZE bits from the register indicated by the DWARF register
+     number DWREGNUM starting at bit BITOFFSET into BUF.  */
+  void read_reg (gdb_byte *buf, size_t bitoffset, size_t bitsize,
+		 int dwregnum);
+
   /* Deref ADDR with size SIZE and return a value of type TYPE.
      If TYPE == nullptr, defaults to this->address_type ().  */
   value *deref (CORE_ADDR addr, int size, struct type *type = nullptr);
diff --git a/gdb/dwarf2/loc.c b/gdb/dwarf2/loc.c
index 8e2b401ba34..d19695d96bd 100644
--- a/gdb/dwarf2/loc.c
+++ b/gdb/dwarf2/loc.c
@@ -2100,6 +2100,7 @@ dwarf2_get_symbol_read_needs (gdb::array_view<const gdb_byte> expr,
 	case DW_OP_GNU_parameter_ref:
 	case DW_OP_regval_type:
 	case DW_OP_GNU_regval_type:
+	case DW_OP_INTEL_regval_bits:
 	  symbol_needs = SYMBOL_NEEDS_FRAME;
 	  break;
 
@@ -3348,6 +3349,7 @@ disassemble_dwarf_expression (struct ui_file *stream,
 	  break;
 
 	case DW_OP_const1u:
+	case DW_OP_INTEL_regval_bits:
 	  ul = extract_unsigned_integer (data, 1, gdbarch_byte_order (arch));
 	  data += 1;
 	  gdb_printf (stream, " %s", pulongest (ul));
diff --git a/include/dwarf2.def b/include/dwarf2.def
index 22b4b7d5b5a..056bb51a280 100644
--- a/include/dwarf2.def
+++ b/include/dwarf2.def
@@ -699,6 +699,10 @@ DW_OP (DW_OP_GNU_const_index, 0xfc)
 /* The GNU variable value extension.
    See http://dwarfstd.org/ShowIssue.php?issue=161109.2 . */
 DW_OP (DW_OP_GNU_variable_value, 0xfd)
+/* https://dwarfstd.org/ShowIssue.php?issue=201007.1
+
+   The DW_OP_regval_bits operation extracts a value from a register.  */
+DW_OP (DW_OP_INTEL_regval_bits, 0xfe)
 /* HP extensions.  */
 DW_OP_DUP (DW_OP_HP_unknown, 0xe0) /* Ouch, the same as GNU_push_tls_address.  */
 DW_OP (DW_OP_HP_is_value, 0xe1)
-- 
2.43.0

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