[gdb/testsuite] Add .debug_loc support in dwarf assembler

Add .debug_loc support in the dwarf assembler, and use it in new test-case
gdb.dwarf2/loc-sec-offset.exp (which is based on
gdb.dwarf2/loclists-sec-offset.exp).

Tested on x86_64-linux.

gdb/testsuite/gdb.dwarf2/loc-sec-offset.c

@@ -0,0 +1,37 @@
+/* Copyright (C) 2021 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+static int
+func1 (void)
+{
+  asm ("func1_label: .global func1_label\n");
+  return 1;
+}
+
+static int
+func2 (void)
+{
+  asm ("func2_label: .global func2_label\n");
+  return 2;
+}
+
+int
+main (void)
+{
+  func1 ();
+  func2 ();
+}

gdb/testsuite/gdb.dwarf2/loc-sec-offset.exp

@@ -0,0 +1,121 @@
+# Copyright 2021 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Test DW_AT_location attribute referencing the .debug_loc section using
+# the DW_FORM_sec_offset form.
+
+load_lib dwarf.exp
+
+if {![dwarf2_support]} {
+    return 0
+}
+
+# Test with 32-bit and 64-bit DWARF.
+foreach_with_prefix is_64 {false true} {
+    if { $is_64 } {
+	standard_testfile .c -dw64.S
+	set testfile ${testfile}-dw64
+    } else {
+	standard_testfile .c -dw32.S
+	set testfile ${testfile}-dw32
+    }
+
+    lassign [function_range func1 $srcdir/$subdir/$srcfile] \
+	func1_addr func1_len
+    lassign [function_range func2 $srcdir/$subdir/$srcfile] \
+	func2_addr func2_len
+
+    set asm_file [standard_output_file $srcfile2]
+    Dwarf::assemble $asm_file {
+	global func1_addr func1_len
+	global func2_addr func2_len
+	global is_64
+
+	set cu_version 4
+
+	cu {
+	    version $cu_version
+	    is_64 $is_64
+	} {
+	    declare_labels int_type1
+	    declare_labels foo_location_list
+
+	    DW_TAG_compile_unit {
+	    } {
+		int_type1: DW_TAG_base_type {
+		    {DW_AT_byte_size 4 DW_FORM_data1}
+		    {DW_AT_encoding @DW_ATE_signed}
+		    {DW_AT_name "int"}
+		}
+
+		DW_TAG_variable {
+		    {DW_AT_name "foo"}
+		    {DW_AT_location $foo_location_list DW_FORM_sec_offset}
+		    {DW_AT_type :$int_type1}
+		}
+
+		DW_TAG_subprogram {
+		    {DW_AT_name "func1"}
+		    {DW_AT_low_pc $func1_addr}
+		    {DW_AT_high_pc $func1_len DW_FORM_udata}
+		}
+
+		DW_TAG_subprogram {
+		    {DW_AT_name "func2"}
+		    {DW_AT_low_pc $func2_addr}
+		    {DW_AT_high_pc $func2_len DW_FORM_udata}
+		}
+	    }
+	}
+
+	# Generate a .debug_loc contribution.
+	loc {
+	    cu_is_64 $is_64
+	    cu_version $cu_version
+	} {
+	    foo_location_list:
+	    entry $func1_addr "$func1_addr + $func1_len" {
+		DW_OP_constu 0x123456
+		DW_OP_stack_value
+	    }
+	    entry $func2_addr "$func2_addr + $func2_len" {
+		DW_OP_constu 0x234567
+		DW_OP_stack_value
+	    }
+	}
+    }
+
+    if { [prepare_for_testing "failed to prepare" ${testfile} \
+	      [list $srcfile $asm_file] {nodebug}] } {
+	return -1
+    }
+
+    if { ![runto_main] } {
+	return
+    }
+
+    gdb_breakpoint "func1"
+    gdb_breakpoint "func2"
+
+    gdb_continue_to_breakpoint "func1"
+    with_test_prefix "at func1" {
+	gdb_test "print /x foo" " = 0x123456"
+    }
+
+    gdb_continue_to_breakpoint "func2"
+    with_test_prefix "at func2" {
+	gdb_test "print /x foo" " = 0x234567"
+    }
+}

gdb/testsuite/lib/dwarf.exp

@@ -2369,6 +2369,105 @@ namespace eval Dwarf {
 	aranges_end:
     }
 
+    # Emit a .debug_loc entry.
+
+    proc _loc_entry { start end location_description } {
+	# Determine how to emit addresses.
+	variable _addr_size
+	if { $_addr_size == 8 } {
+	    set addr_op .8byte
+	} elseif { $_addr_size == 4 } {
+	    set addr_op .4byte
+	}
+
+	# Emit start and end address.
+	_op $addr_op $start "Start address"
+	_op $addr_op $end "End address"
+
+	declare_labels location_description_start
+	declare_labels location_description_end
+
+	# Emit length of location description.
+	set len "$location_description_end - $location_description_start"
+	_op .2byte $len "Location description length"
+
+	# Tag start of location description.
+	define_label $location_description_start
+
+	# Emit location description.
+	variable _cu_version
+	variable _cu_offset_size
+	_location $location_description $_cu_version $_addr_size \
+	    $_cu_offset_size
+
+	# Tag end of location description.
+	define_label $location_description_end
+    }
+
+    # Emit a DWARF .debug_loc contribution.
+    #
+    # OPTIONS is a list with an even number of elements containing
+    # option-name and option-value pairs.
+    # Current options are:
+    # cu_is_64 0|1 - boolean indicating if references from location
+    #                descriptions refer to a 64-bit DWARF CU.
+    #                default = 0 (32-bit)
+    # cu_version n - section version of DWARF CU referenced from location
+    #                descriptions.
+    #                default = 4
+    #
+    # BODY is Tcl code that emits the parts which make up the body of
+    # the debug_loc contribution.  It is evaluated in the caller's context.
+    # The following command is available for the BODY section:
+    #
+    #   entry <start> <end> <location description>
+    #     -- emit a .debug_loc entry
+
+    proc loc { options body } {
+	# Handle options.
+	parse_options {
+	    { cu_version 4 }
+	    { cu_is_64 0 }
+	}
+
+	# Export for use in BODY.
+	variable _addr_size
+	if { [is_64_target] } {
+	    set _addr_size 8
+	} else {
+	    set _addr_size 4
+	}
+	variable _cu_version
+	set _cu_version $cu_version
+	variable _cu_offset_size
+	if { $cu_is_64 == 1 } {
+	    set _cu_offset_size 8
+	} else {
+	    set _cu_offset_size 4
+	}
+
+	# Switch to .debug_loc section.
+	_section .debug_loc
+
+	# Introduce command 'entry'.
+	with_override Dwarf::entry Dwarf::_loc_entry {
+	    # Emit entries.
+	    uplevel $body
+	}
+
+	# Determine how to emit addresses.
+	if { $_addr_size == 8 } {
+	    set addr_op .8byte
+	} elseif { $_addr_size == 4 } {
+	    set addr_op .4byte
+	}
+
+	# Emit <End of list>.
+	set comment "<End of list>"
+	_op $addr_op 0 "$comment (Part 1/2)"
+	_op $addr_op 0 "$comment (Part 2/2)"
+    }
+
     proc _empty_array {name} {
 	upvar $name the_array