gdb/testsuite: Add is-stmt support to the DWARF compiler

This commit adds the ability to set and toggle the DWARF line table
is-stmt flag.

A DWARF line table can now be created with the attribute
'default_is_stmt' like this:

  lines {version 2 default_is_stmt 0} label {
    ...
  }

If 'default_is_stmt' is not specified then the current default is 1,
which matches the existing behaviour.

Inside the DWARF line table program you can now make use of
{DW_LNS_negate_stmt} to toggle the is-stmt flag, for example this
meaningless program:

  lines {version 2 default_is_stmt 0} label {
    include_dir "some_directory"
    file_name "some_filename" 1

    program {
      {DW_LNS_negate_stmt}
      {DW_LNE_end_sequence}
    }
  }

This new functionality will be used in a later commit.

gdb/testsuite/ChangeLog:

	* lib/dwarf.exp (Dwarf::lines) Add support for modifying the
	is-stmt flag in the line table.

Change-Id: Ia3f61d523826382dd2333f65b9aae368ad29c4a5

2 files changed, 12 insertions, 1 deletions

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index f9e0c20..a98e56d 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2020-03-10  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* lib/dwarf.exp (Dwarf::lines) Add support for modifying the
+	is-stmt flag in the line table.
+
 2020-03-09  Tom de Vries  <tdevries@suse.de>
 
 	* lib/gdb.exp (cached_file): Create cache dir.
diff --git a/gdb/testsuite/lib/dwarf.exp b/gdb/testsuite/lib/dwarf.exp
index 6c6ffbe..417b22d 100644
--- a/gdb/testsuite/lib/dwarf.exp
+++ b/gdb/testsuite/lib/dwarf.exp
@@ -1311,12 +1311,14 @@ namespace eval Dwarf {
 	set _unit_addr_size default
 	set _line_saw_program 0
 	set _line_saw_file 0
+	set _default_is_stmt 1
 
 	foreach { name value } $options {
 	    switch -exact -- $name {
 		is_64 { set is_64 $value }
 		version { set _unit_version $value }
 		addr_size { set _unit_addr_size $value }
+		default_is_stmt { set _default_is_stmt $value }
 		default { error "unknown option $name" }
 	    }
 	}
@@ -1363,7 +1365,7 @@ namespace eval Dwarf {
 	define_label $header_len_label
 
 	_op .byte 1 "minimum_instruction_length"
-	_op .byte 1 "default_is_stmt"
+	_op .byte $_default_is_stmt "default_is_stmt"
 	_op .byte 1 "line_base"
 	_op .byte 1 "line_range"
 	_op .byte 10 "opcode_base"
@@ -1438,6 +1440,10 @@ namespace eval Dwarf {
 		_op .byte 1
 	    }
 
+	    proc DW_LNS_negate_stmt {} {
+		_op .byte 6
+	    }
+
 	    proc DW_LNS_advance_pc {offset} {
 		_op .byte 2
 		_op .uleb128 ${offset}