GDB 7.6.50

gdb/testsuite/lib/dwarf.exp

-# Copyright 2010, 2012 Free Software Foundation, Inc.
+# Copyright 2010-2013 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/>.
 
 # Return true if the target supports DWARF-2 and uses gas.
 # For now pick a sampling of likely targets.
 proc dwarf2_support {} {
     if {[istarget *-*-linux*]
         || [istarget *-*-gnu*]
         || [istarget *-*-elf*]
         || [istarget *-*-openbsd*]
         || [istarget arm*-*-eabi*]
         || [istarget arm*-*-symbianelf*]
         || [istarget powerpc-*-eabi*]} {
         return 1
     }
 
     return 0
 }
+
+# Build an executable from a fission-based .S file.
+# This handles the extra work of splitting the .o into non-dwo and dwo
+# pieces, making sure the .dwo is available if we're using cc-with-tweaks.sh
+# to build a .dwp file.
+# The arguments and results are the same as for build_executable.
+#
+# Current restrictions:
+# - only supports one source file
+# - cannot be run on remote hosts
+
+proc build_executable_from_fission_assembler { testname executable sources options } {
+    verbose -log "build_executable_from_fission_assembler $testname $executable $sources $options"
+    if { [llength $sources] != 1 } {
+        error "Only one source file supported."
+    }
+    if [is_remote host] {
+        error "Remote hosts are not supported."
+    }
+
+    global srcdir subdir
+    set source_file ${srcdir}/${subdir}/${sources}
+    set root_name [file rootname [file tail $source_file]]
+    set output_base [standard_output_file $root_name]
+    set object_file ${output_base}.o
+    set dwo_file ${output_base}.dwo
+    set object_options "object $options"
+    set objcopy [gdb_find_objcopy]
+
+    set result [gdb_compile $source_file $object_file object $options]
+    if { "$result" != "" } {
+        return -1
+    }
+
+    set command "$objcopy --extract-dwo $object_file $dwo_file"
+    verbose -log "Executing $command"
+    set result [catch "exec $command" output]
+    verbose -log "objcopy --extract-dwo output: $output"
+    if { $result == 1 } {
+        return -1
+    }
+
+    set command "$objcopy --strip-dwo $object_file"
+    verbose -log "Executing $command"
+    set result [catch "exec $command" output]
+    verbose -log "objcopy --strip-dwo output: $output"
+    if { $result == 1 } {
+        return -1
+    }
+
+    set result [gdb_compile $object_file $executable executable {nodebug}]
+    if { "$result" != "" } {
+        return -1
+    }
+
+    return 0
+}
+
+# A DWARF assembler.
+#
+# All the variables in this namespace are private to the
+# implementation.  Also, any procedure whose name starts with "_" is
+# private as well.  Do not use these.
+#
+# Exported functions are documented at their definition.
+#
+# In addition to the hand-written functions documented below, this
+# module automatically generates a function for each DWARF tag.  For
+# most tags, two forms are made: a full name, and one with the
+# "DW_TAG_" prefix stripped.  For example, you can use either
+# 'DW_TAG_compile_unit' or 'compile_unit' interchangeably.
+#
+# There are two exceptions to this rule: DW_TAG_variable and
+# DW_TAG_namespace.  For these, the full name must always be used,
+# as the short name conflicts with Tcl builtins.  (Should future
+# versions of Tcl or DWARF add more conflicts, this list will grow.
+# If you want to be safe you should always use the full names.)
+#
+# Each tag procedure is defined like:
+#
+# proc DW_TAG_mumble {{attrs {}} {children {}}} { ... }
+#
+# ATTRS is an optional list of attributes.
+# It is run through 'subst' in the caller's context before processing.
+#
+# Each attribute in the list has one of two forms:
+#   1. { NAME VALUE }
+#   2. { NAME VALUE FORM }
+#
+# In each case, NAME is the attribute's name.
+# This can either be the full name, like 'DW_AT_name', or a shortened
+# name, like 'name'.  These are fully equivalent.
+#
+# If FORM is given, it should name a DW_FORM_ constant.
+# This can either be the short form, like 'DW_FORM_addr', or a
+# shortened version, like 'addr'.  If the form is given, VALUE
+# is its value; see below.  In some cases, additional processing
+# is done; for example, DW_FORM_strp manages the .debug_str
+# section automatically.
+#
+# If FORM is 'SPECIAL_expr', then VALUE is treated as a location
+# expression.  The effective form is then DW_FORM_block, and VALUE
+# is passed to the (internal) '_location' proc to be translated.
+# This proc implements a miniature DW_OP_ assembler.
+#
+# If FORM is not given, it is guessed:
+# * If VALUE starts with the "@" character, the rest of VALUE is
+#   looked up as a DWARF constant, and DW_FORM_sdata is used.  For
+#   example, '@DW_LANG_c89' could be used.
+# * If VALUE starts with the ":" character, then it is a label
+#   reference.  The rest of VALUE is taken to be the name of a label,
+#   and DW_FORM_ref4 is used.  See 'new_label' and 'define_label'.
+# * Otherwise, VALUE is taken to be a string and DW_FORM_string is
+#   used.
+# More form-guessing functionality may be added.
+#
+# CHILDREN is just Tcl code that can be used to define child DIEs.  It
+# is evaluated in the caller's context.
+#
+# Currently this code is missing nice support for CFA handling, and
+# probably other things as well.
+
+namespace eval Dwarf {
+    # True if the module has been initialized.
+    variable _initialized 0
+
+    # Constants from dwarf2.h.
+    variable _constants
+    # DW_AT short names.
+    variable _AT
+    # DW_FORM short names.
+    variable _FORM
+    # DW_OP short names.
+    variable _OP
+
+    # The current output file.
+    variable _output_file
+
+    # Note: The _cu_ values here also apply to type units (TUs).
+    # Think of a TU as a special kind of CU.
+
+    # Current CU count.
+    variable _cu_count
+
+    # The current CU's base label.
+    variable _cu_label
+
+    # The current CU's version.
+    variable _cu_version
+
+    # The current CU's address size.
+    variable _cu_addr_size
+    # The current CU's offset size.
+    variable _cu_offset_size
+
+    # Label generation number.
+    variable _label_num
+
+    # The deferred output array.  The index is the section name; the
+    # contents hold the data for that section.
+    variable _deferred_output
+
+    # If empty, we should write directly to the output file.
+    # Otherwise, this is the name of a section to write to.
+    variable _defer
+
+    # The abbrev section.  Typically .debug_abbrev but can be .debug_abbrev.dwo
+    # for Fission.
+    variable _abbrev_section
+
+    # The next available abbrev number in the current CU's abbrev
+    # table.
+    variable _abbrev_num
+
+    # The string table for this assembly.  The key is the string; the
+    # value is the label for that string.
+    variable _strings
+
+    proc _process_one_constant {name value} {
+        variable _constants
+        variable _AT
+        variable _FORM
+        variable _OP
+
+        set _constants($name) $value
+
+        if {![regexp "^DW_(\[A-Z\]+)_(\[A-Za-z0-9_\]+)$" $name \
+                  ignore prefix name2]} {
+            error "non-matching name: $name"
+        }
+
+        if {$name2 == "lo_user" || $name2 == "hi_user"} {
+            return
+        }
+
+        # We only try to shorten some very common things.
+        # FIXME: CFA?
+        switch -exact -- $prefix {
+            TAG {
+                # Create two procedures for the tag.  These call
+                # _handle_DW_TAG with the full tag name baked in; this
+                # does all the actual work.
+                proc $name {{attrs {}} {children {}}} \
+                    "_handle_DW_TAG $name \$attrs \$children"
+
+                # Filter out ones that are known to clash.
+                if {$name2 == "variable" || $name2 == "namespace"} {
+                    set name2 "tag_$name2"
+                }
+
+                if {[info commands $name2] != {}} {
+                    error "duplicate proc name: from $name"
+                }
+
+                proc $name2 {{attrs {}} {children {}}} \
+                    "_handle_DW_TAG $name \$attrs \$children"
+            }
+
+            AT {
+                set _AT($name2) $name
+            }
+
+            FORM {
+                set _FORM($name2) $name
+            }
+
+            OP {
+                set _OP($name2) $name
+            }
+
+            default {
+                return
+            }
+        }
+    }
+
+    proc _read_constants {} {
+        global srcdir hex decimal
+        variable _constants
+
+        # DWARF name-matching regexp.
+        set dwrx "DW_\[a-zA-Z0-9_\]+"
+        # Whitespace regexp.
+        set ws "\[ \t\]+"
+
+        set fd [open [file join $srcdir .. .. include dwarf2.h]]
+        while {![eof $fd]} {
+            set line [gets $fd]
+            if {[regexp -- "^${ws}($dwrx)${ws}=${ws}($hex|$decimal),?$" \
+                     $line ignore name value ignore2]} {
+                _process_one_constant $name $value
+            }
+        }
+        close $fd
+
+        set fd [open [file join $srcdir .. .. include dwarf2.def]]
+        while {![eof $fd]} {
+            set line [gets $fd]
+            if {[regexp -- \
+                     "^DW_\[A-Z_\]+${ws}\\(($dwrx),${ws}($hex|$decimal)\\)$" \
+                     $line ignore name value ignore2]} {
+                _process_one_constant $name $value
+            }
+        }
+        close $fd
+
+        set _constants(SPECIAL_expr) $_constants(DW_FORM_block)
+    }
+
+    proc _quote {string} {
+        # FIXME
+        return "\"${string}\\0\""
+    }
+
+    proc _nz_quote {string} {
+        # For now, no quoting is done.
+        return "\"${string}\""
+    }
+
+    proc _handle_DW_FORM {form value} {
+        switch -exact -- $form {
+            DW_FORM_string  {
+                _op .ascii [_quote $value]
+            }
+
+            DW_FORM_flag_present {
+                # We don't need to emit anything.
+            }
+
+            DW_FORM_data4 -
+            DW_FORM_ref4 {
+                _op .4byte $value
+            }
+
+            DW_FORM_ref_addr {
+                variable _cu_offset_size
+                variable _cu_version
+                variable _cu_addr_size
+
+                if {$_cu_version == 2} {
+                    set size $_cu_addr_size
+                } else {
+                    set size $_cu_offset_size
+                }
+
+                _op .${size}byte $value
+            }
+
+            DW_FORM_ref1 -
+            DW_FORM_flag -
+            DW_FORM_data1 {
+                _op .byte $value
+            }
+
+            DW_FORM_sdata {
+                _op .sleb128 $value
+            }
+
+            DW_FORM_ref_udata -
+            DW_FORM_udata {
+                _op .uleb128 $value
+            }
+
+            DW_FORM_addr {
+                variable _cu_addr_size
+
+                _op .${_cu_addr_size}byte $value
+            }
+
+            DW_FORM_data2 -
+            DW_FORM_ref2 {
+                _op .2byte $value
+            }
+
+            DW_FORM_data8 -
+            DW_FORM_ref8 -
+            DW_FORM_ref_sig8 {
+                _op .8byte $value
+            }
+
+            DW_FORM_strp {
+                variable _strings
+                variable _cu_offset_size
+
+                if {![info exists _strings($value)]} {
+                    set _strings($value) [new_label strp]
+                    _defer_output .debug_string {
+                        define_label $_strings($value)
+                        _op .ascii [_quote $value]
+                    }
+                }
+
+                _op .${_cu_offset_size}byte $_strings($value) "strp: $value"
+            }
+
+            SPECIAL_expr {
+                set l1 [new_label "expr_start"]
+                set l2 [new_label "expr_end"]
+                _op .uleb128 "$l2 - $l1" "expression"
+                define_label $l1
+                _location $value
+                define_label $l2
+            }
+
+            DW_FORM_block1 {
+                set len [string length $value]
+                if {$len > 255} {
+                    error "DW_FORM_block1 length too long"
+                }
+                _op .byte $len
+                _op .ascii [_nz_quote $value]
+            }
+
+            DW_FORM_block2 -
+            DW_FORM_block4 -
+
+            DW_FORM_block -
+
+            DW_FORM_ref2 -
+            DW_FORM_indirect -
+            DW_FORM_sec_offset -
+            DW_FORM_exprloc -
+
+            DW_FORM_GNU_addr_index -
+            DW_FORM_GNU_str_index -
+            DW_FORM_GNU_ref_alt -
+            DW_FORM_GNU_strp_alt -
+
+            default {
+                error "unhandled form $form"
+            }
+        }
+    }
+
+    proc _guess_form {value varname} {
+        upvar $varname new_value
+
+        switch -exact -- [string range $value 0 0] {
+            @ {
+                # Constant reference.
+                variable _constants
+
+                set new_value $_constants([string range $value 1 end])
+                # Just the simplest.
+                return DW_FORM_sdata
+            }
+
+            : {
+                # Label reference.
+                variable _cu_label
+
+                set new_value "[string range $value 1 end] - $_cu_label"
+
+                return DW_FORM_ref4
+            }
+
+            default {
+                return DW_FORM_string
+            }
+        }
+    }
+
+    # Map NAME to its canonical form.
+    proc _map_name {name ary} {
+        variable $ary
+
+        if {[info exists ${ary}($name)]} {
+            set name [set ${ary}($name)]
+        }
+
+        return $name
+    }
+
+    proc _handle_DW_TAG {tag_name {attrs {}} {children {}}} {
+        variable _abbrev_section
+        variable _abbrev_num
+        variable _constants
+
+        set has_children [expr {[string length $children] > 0}]
+        set my_abbrev [incr _abbrev_num]
+
+        # We somewhat wastefully emit a new abbrev entry for each tag.
+        # There's no reason for this other than laziness.
+        _defer_output $_abbrev_section {
+            _op .uleb128 $my_abbrev "Abbrev start"
+            _op .uleb128 $_constants($tag_name) $tag_name
+            _op .byte $has_children "has_children"
+        }
+
+        _op .uleb128 $my_abbrev "Abbrev ($tag_name)"
+
+        foreach attr $attrs {
+            set attr_name [_map_name [lindex $attr 0] _AT]
+            set attr_value [uplevel 2 [list subst [lindex $attr 1]]]
+            if {[llength $attr] > 2} {
+                set attr_form [lindex $attr 2]
+            } else {
+                set attr_form [_guess_form $attr_value attr_value]
+            }
+            set attr_form [_map_name $attr_form _FORM]
+
+            _handle_DW_FORM $attr_form $attr_value
+
+            _defer_output $_abbrev_section {
+                _op .uleb128 $_constants($attr_name) $attr_name
+                _op .uleb128 $_constants($attr_form) $attr_form
+            }
+        }
+
+        _defer_output $_abbrev_section {
+            # Terminator.
+            _op .byte 0x0 Terminator
+            _op .byte 0x0 Terminator
+        }
+
+        if {$has_children} {
+            uplevel 2 $children
+
+            # Terminate children.
+            _op .byte 0x0 "Terminate children"
+        }
+    }
+
+    proc _emit {string} {
+        variable _output_file
+        variable _defer
+        variable _deferred_output
+
+        if {$_defer == ""} {
+            puts $_output_file $string
+        } else {
+            append _deferred_output($_defer) ${string}\n
+        }
+    }
+
+    proc _section {name {flags ""} {type ""}} {
+        if {$flags == "" && $type == ""} {
+            _emit "        .section $name"
+        } elseif {$type == ""} {
+            _emit "        .section $name, \"$flags\""
+        } else {
+            _emit "        .section $name, \"$flags\", %$type"
+        }
+    }
+
+    # SECTION_SPEC is a list of arguments to _section.
+    proc _defer_output {section_spec body} {
+        variable _defer
+        variable _deferred_output
+
+        set old_defer $_defer
+        set _defer [lindex $section_spec 0]
+
+        if {![info exists _deferred_output($_defer)]} {
+            set _deferred_output($_defer) ""
+            eval _section $section_spec
+        }
+
+        uplevel $body
+
+        set _defer $old_defer
+    }
+
+    proc _defer_to_string {body} {
+        variable _defer
+        variable _deferred_output
+
+        set old_defer $_defer
+        set _defer temp
+
+        set _deferred_output($_defer) ""
+
+        uplevel $body
+
+        set result $_deferred_output($_defer)
+        unset _deferred_output($_defer)
+
+        set _defer $old_defer
+        return $result
+    }
+
+    proc _write_deferred_output {} {
+        variable _output_file
+        variable _deferred_output
+
+        foreach section [array names _deferred_output] {
+            # The data already has a newline.
+            puts -nonewline $_output_file $_deferred_output($section)
+        }
+
+        # Save some memory.
+        unset _deferred_output
+    }
+
+    proc _op {name value {comment ""}} {
+        set text "        ${name}        ${value}"
+        if {$comment != ""} {
+            # Try to make stuff line up nicely.
+            while {[string length $text] < 40} {
+                append text " "
+            }
+            append text "/* ${comment} */"
+        }
+        _emit $text
+    }
+
+    proc _compute_label {name} {
+        return ".L${name}"
+    }
+
+    # Return a name suitable for use as a label.  If BASE_NAME is
+    # specified, it is incorporated into the label name; this is to
+    # make debugging the generated assembler easier.  If BASE_NAME is
+    # not specified a generic default is used.  This proc does not
+    # define the label; see 'define_label'.  'new_label' attempts to
+    # ensure that label names are unique.
+    proc new_label {{base_name label}} {
+        variable _label_num
+
+        return [_compute_label ${base_name}[incr _label_num]]
+    }
+
+    # Define a label named NAME.  Ordinarily, NAME comes from a call
+    # to 'new_label', but this is not required.
+    proc define_label {name} {
+        _emit "${name}:"
+    }
+
+    # Declare a global label.  This is typically used to refer to
+    # labels defined in other files, for example a function defined in
+    # a .c file.
+    proc extern {args} {
+        foreach name $args {
+            _op .global $name
+        }
+    }
+
+    # A higher-level interface to label handling.
+    #
+    # ARGS is a list of label descriptors.  Each one is either a
+    # single element, or a list of two elements -- a name and some
+    # text.  For each descriptor, 'new_label' is invoked.  If the list
+    # form is used, the second element in the list is passed as an
+    # argument.  The label name is used to define a variable in the
+    # enclosing scope; this can be used to refer to the label later.
+    # The label name is also used to define a new proc whose name is
+    # the label name plus a trailing ":".  This proc takes a body as
+    # an argument and can be used to define the label at that point;
+    # then the body, if any, is evaluated in the caller's context.
+    #
+    # For example:
+    #
+    # declare_labels int_label
+    # something { ... $int_label }   ;# refer to the label
+    # int_label: constant { ... }    ;# define the label
+    proc declare_labels {args} {
+        foreach arg $args {
+            set name [lindex $arg 0]
+            set text [lindex $arg 1]
+
+            upvar $name label_var
+            if {$text == ""} {
+                set label_var [new_label]
+            } else {
+                set label_var [new_label $text]
+            }
+
+            proc ${name}: {args} [format {
+                define_label %s
+                uplevel $args
+            } $label_var]
+        }
+    }
+
+    # This is a miniature assembler for location expressions.  It is
+    # suitable for use in the attributes to a DIE.  Its output is
+    # prefixed with "=" to make it automatically use DW_FORM_block.
+    # BODY is split by lines, and each line is taken to be a list.
+    # (FIXME should use 'info complete' here.)
+    # Each list's first element is the opcode, either short or long
+    # forms are accepted.
+    # FIXME argument handling
+    # FIXME move docs
+    proc _location {body} {
+        variable _constants
+        variable _cu_label
+        variable _cu_addr_size
+        variable _cu_offset_size
+
+        foreach line [split $body \n] {
+            if {[lindex $line 0] == ""} {
+                continue
+            }
+            set opcode [_map_name [lindex $line 0] _OP]
+            _op .byte $_constants($opcode) $opcode
+
+            switch -exact -- $opcode {
+                DW_OP_addr {
+                    _op .${_cu_addr_size}byte [lindex $line 1]
+                }
+
+                DW_OP_const1u -
+                DW_OP_const1s {
+                    _op .byte [lindex $line 1]
+                }
+
+                DW_OP_const2u -
+                DW_OP_const2s {
+                    _op .2byte [lindex $line 1]
+                }
+
+                DW_OP_const4u -
+                DW_OP_const4s {
+                    _op .4byte [lindex $line 1]
+                }
+
+                DW_OP_const8u -
+                DW_OP_const8s {
+                    _op .8byte [lindex $line 1]
+                }
+
+                DW_OP_constu {
+                    _op .uleb128 [lindex $line 1]
+                }
+                DW_OP_consts {
+                    _op .sleb128 [lindex $line 1]
+                }
+
+                DW_OP_plus_uconst {
+                    _op .uleb128 [lindex $line 1]
+                }
+
+                DW_OP_piece {
+                    _op .uleb128 [lindex $line 1]
+                }
+
+                DW_OP_bit_piece {
+                    _op .uleb128 [lindex $line 1]
+                    _op .uleb128 [lindex $line 2]
+                }
+
+                DW_OP_GNU_implicit_pointer {
+                    if {[llength $line] != 3} {
+                        error "usage: DW_OP_GNU_implicit_pointer LABEL OFFSET"
+                    }
+
+                    # Here label is a section offset.
+                    set label [lindex $line 1]
+                    _op .${_cu_offset_size}byte $label
+                    _op .sleb128 [lindex $line 2]
+                }
+
+                DW_OP_deref_size {
+                    if {[llength $line] != 2} {
+                        error "usage: DW_OP_deref_size SIZE"
+                    }
+
+                    _op .byte [lindex $line 1]
+                }
+
+                default {
+                    if {[llength $line] > 1} {
+                        error "Unimplemented: operands in location for $opcode"
+                    }
+                }
+            }
+        }
+    }
+
+    # Emit a DWARF CU.
+    # OPTIONS is a list with an even number of elements containing
+    # option-name and option-value pairs.
+    # Current options are:
+    # is_64 0|1    - boolean indicating if you want to emit 64-bit DWARF
+    #                default = 0 (32-bit)
+    # version n    - DWARF version number to emit
+    #                default = 4
+    # addr_size n  - the size of addresses, 32, 64, or default
+    #                default = default
+    # fission 0|1  - boolean indicating if generating Fission debug info
+    #                default = 0
+    # BODY is Tcl code that emits the DIEs which make up the body of
+    # the CU.  It is evaluated in the caller's context.
+    proc cu {options body} {
+        variable _cu_count
+        variable _abbrev_section
+        variable _abbrev_num
+        variable _cu_label
+        variable _cu_version
+        variable _cu_addr_size
+        variable _cu_offset_size
+
+        # Establish the defaults.
+        set is_64 0
+        set _cu_version 4
+        set _cu_addr_size default
+        set fission 0
+        set section ".debug_info"
+        set _abbrev_section ".debug_abbrev"
+
+        foreach { name value } $options {
+            switch -exact -- $name {
+                is_64 { set is_64 $value }
+                version { set _cu_version $value }
+                addr_size { set _cu_addr_size $value }
+                fission { set fission $value }
+                default { error "unknown option $name" }
+            }
+        }
+        if {$_cu_addr_size == "default"} {
+            if {[is_64_target]} {
+                set _cu_addr_size 8
+            } else {
+                set _cu_addr_size 4
+            }
+        }
+        set _cu_offset_size [expr { $is_64 ? 8 : 4 }]
+        if { $fission } {
+            set section ".debug_info.dwo"
+            set _abbrev_section ".debug_abbrev.dwo"
+        }
+
+        _section $section
+
+        set cu_num [incr _cu_count]
+        set my_abbrevs [_compute_label "abbrev${cu_num}_begin"]
+        set _abbrev_num 1
+
+        set _cu_label [_compute_label "cu${cu_num}_begin"]
+        set start_label [_compute_label "cu${cu_num}_start"]
+        set end_label [_compute_label "cu${cu_num}_end"]
+        
+        define_label $_cu_label
+        if {$is_64} {
+            _op .4byte 0xffffffff
+            _op .8byte "$end_label - $start_label"
+        } else {
+            _op .4byte "$end_label - $start_label"
+        }
+        define_label $start_label
+        _op .2byte $_cu_version Version
+        _op .4byte $my_abbrevs Abbrevs
+        _op .byte $_cu_addr_size "Pointer size"
+
+        _defer_output $_abbrev_section {
+            define_label $my_abbrevs
+        }
+
+        uplevel $body
+
+        _defer_output $_abbrev_section {
+            # Emit the terminator.
+            _op .byte 0x0 Terminator
+            _op .byte 0x0 Terminator
+        }
+
+        define_label $end_label
+    }
+
+    # Emit a DWARF TU.
+    # OPTIONS is a list with an even number of elements containing
+    # option-name and option-value pairs.
+    # Current options are:
+    # is_64 0|1    - boolean indicating if you want to emit 64-bit DWARF
+    #                default = 0 (32-bit)
+    # version n    - DWARF version number to emit
+    #                default = 4
+    # addr_size n  - the size of addresses, 32, 64, or default
+    #                default = default
+    # fission 0|1  - boolean indicating if generating Fission debug info
+    #                default = 0
+    # SIGNATURE is the 64-bit signature of the type.
+    # TYPE_LABEL is the label of the type defined by this TU,
+    # or "" if there is no type (i.e., type stubs in Fission).
+    # BODY is Tcl code that emits the DIEs which make up the body of
+    # the TU.  It is evaluated in the caller's context.
+    proc tu {options signature type_label body} {
+        variable _cu_count
+        variable _abbrev_section
+        variable _abbrev_num
+        variable _cu_label
+        variable _cu_version
+        variable _cu_addr_size
+        variable _cu_offset_size
+
+        # Establish the defaults.
+        set is_64 0
+        set _cu_version 4
+        set _cu_addr_size default
+        set fission 0
+        set section ".debug_types"
+        set _abbrev_section ".debug_abbrev"
+
+        foreach { name value } $options {
+            switch -exact -- $name {
+                is_64 { set is_64 $value }
+                version { set _cu_version $value }
+                addr_size { set _cu_addr_size $value }
+                fission { set fission $value }
+                default { error "unknown option $name" }
+            }
+        }
+        if {$_cu_addr_size == "default"} {
+            if {[is_64_target]} {
+                set _cu_addr_size 8
+            } else {
+                set _cu_addr_size 4
+            }
+        }
+        set _cu_offset_size [expr { $is_64 ? 8 : 4 }]
+        if { $fission } {
+            set section ".debug_types.dwo"
+            set _abbrev_section ".debug_abbrev.dwo"
+        }
+
+        _section $section
+
+        set cu_num [incr _cu_count]
+        set my_abbrevs [_compute_label "abbrev${cu_num}_begin"]
+        set _abbrev_num 1
+
+        set _cu_label [_compute_label "cu${cu_num}_begin"]
+        set start_label [_compute_label "cu${cu_num}_start"]
+        set end_label [_compute_label "cu${cu_num}_end"]
+
+        define_label $_cu_label
+        if {$is_64} {
+            _op .4byte 0xffffffff
+            _op .8byte "$end_label - $start_label"
+        } else {
+            _op .4byte "$end_label - $start_label"
+        }
+        define_label $start_label
+        _op .2byte $_cu_version Version
+        _op .4byte $my_abbrevs Abbrevs
+        _op .byte $_cu_addr_size "Pointer size"
+        _op .8byte $signature Signature
+        if { $type_label != "" } {
+            uplevel declare_labels $type_label
+            upvar $type_label my_type_label
+            if {$is_64} {
+                _op .8byte "$my_type_label - $_cu_label"
+            } else {
+                _op .4byte "$my_type_label - $_cu_label"
+            }
+        } else {
+            if {$is_64} {
+                _op .8byte 0
+            } else {
+                _op .4byte 0
+            }
+        }
+
+        _defer_output $_abbrev_section {
+            define_label $my_abbrevs
+        }
+
+        uplevel $body
+
+        _defer_output $_abbrev_section {
+            # Emit the terminator.
+            _op .byte 0x0 Terminator
+            _op .byte 0x0 Terminator
+        }
+
+        define_label $end_label
+    }
+
+    proc _empty_array {name} {
+        upvar $name the_array
+
+        catch {unset the_array}
+        set the_array(_) {}
+        unset the_array(_)
+    }
+
+    # Emit a .gnu_debugaltlink section with the given file name and
+    # build-id.  The buildid should be represented as a hexadecimal
+    # string, like "ffeeddcc".
+    proc gnu_debugaltlink {filename buildid} {
+        _defer_output .gnu_debugaltlink {
+            _op .ascii [_quote $filename]
+            foreach {a b} [split $buildid {}] {
+                _op .byte 0x$a$b
+            }
+        }
+    }
+
+    proc _note {type name hexdata} {
+        set namelen [expr [string length $name] + 1]
+
+        # Name size.
+        _op .4byte $namelen
+        # Data size.
+        _op .4byte [expr [string length $hexdata] / 2]
+        # Type.
+        _op .4byte $type
+        # The name.
+        _op .ascii [_quote $name]
+        # Alignment.
+        set align 2
+        set total [expr {($namelen + (1 << $align) - 1) & (-1 << $align)}]
+        for {set i $namelen} {$i < $total} {incr i} {
+            _op .byte 0
+        }
+        # The data.
+        foreach {a b} [split $hexdata {}] {
+            _op .byte 0x$a$b
+        }
+    }
+
+    # Emit a note section holding the given build-id.
+    proc build_id {buildid} {
+        _defer_output {.note.gnu.build-id a note} {
+            # From elf/common.h.
+            set NT_GNU_BUILD_ID 3
+
+            _note $NT_GNU_BUILD_ID GNU $buildid
+        }
+    }
+
+    # The top-level interface to the DWARF assembler.
+    # FILENAME is the name of the file where the generated assembly
+    # code is written.
+    # BODY is Tcl code to emit the assembly.  It is evaluated via
+    # "eval" -- not uplevel as you might expect, because it is
+    # important to run the body in the Dwarf namespace.
+    #
+    # A typical invocation is something like:
+    #    Dwarf::assemble $file {
+    #        cu 0 2 8 {
+    #            compile_unit {
+    #            ...
+    #            }
+    #        }
+    #        cu 0 2 8 {
+    #        ...
+    #        }
+    #    }
+    proc assemble {filename body} {
+        variable _initialized
+        variable _output_file
+        variable _deferred_output
+        variable _defer
+        variable _label_num
+        variable _strings
+        variable _cu_count
+
+        if {!$_initialized} {
+            _read_constants
+            set _initialized 1
+        }
+
+        set _output_file [open $filename w]
+        set _cu_count 0
+        _empty_array _deferred_output
+        set _defer ""
+        set _label_num 0
+        _empty_array _strings
+
+        # Not "uplevel" here, because we want to evaluate in this
+        # namespace.  This is somewhat bad because it means we can't
+        # readily refer to outer variables.
+        eval $body
+
+        _write_deferred_output
+
+        catch {close $_output_file}
+        set _output_file {}
+    }
+}