Compute the function length instead of hard coding it

In Dwarf::assemble in dwz.exp, 10 is hard-coded in it,

 	    subprogram {
 		{name main}
 		{low_pc main addr}
		{high_pc "main + 10" addr}
 	    }

however, the length of main function varies on architectures.  The
hard-coded 10 here causes dwz.exp fails on some targets, such as
nios2.

This patch is to add some code to compute the length of function main,
which is similar to what we are doing in entry-values.exp.

gdb/testsuite:

2014-04-26  Yao Qi  <yao@codesourcery.com>

	* gdb.dwarf2/dwz.exp: Compile main.c to object.  Restart GDB
	and compute the length of function main.  Save it in
	$main_length.
	(Dwarf::assemble): Use $main_length instead of hard-coded 10.
	(top-level): Use gdb_compile to compile objects into
	executable and restart GDB.  Remove invocation to
	prepare_for_testing.

gdb/testsuite/ChangeLog

@@ -1,3 +1,13 @@
+2014-04-26  Yao Qi  <yao@codesourcery.com>
+
+	* gdb.dwarf2/dwz.exp: Compile main.c to object.  Restart GDB
+	and compute the length of function main.  Save it in
+	$main_length.
+	(Dwarf::assemble): Use $main_length instead of hard-coded 10.
+	(top-level): Use gdb_compile to compile objects into
+	executable and restart GDB.  Remove invocation to
+	prepare_for_testing.
+
 2014-04-25  Simon Marchi  <simon.marchi@ericsson.com>
 	    Pedro Alves  <palves@redhat.com>
 

gdb/testsuite/gdb.dwarf2/dwz.exp

@@ -22,10 +22,56 @@ if {![dwarf2_support]} {
 
 standard_testfile main.c dwz.S
 
+if  {[gdb_compile ${srcdir}/${subdir}/${srcfile} ${binfile}1.o \
+	  object {nodebug}] != ""} {
+    return -1
+}
+
+# Start GDB and load object file, compute the function length which is
+# needed in the Dwarf Assembler below.
+clean_restart ${testfile}1.o
+
+set main_length ""
+set test "disassemble main"
+gdb_test_multiple $test $test {
+    -re ".*$hex <\\+($decimal)>:\[^\r\n\]+\r\nEnd of assembler dump\.\r\n$gdb_prompt $" {
+	set main_length $expect_out(1,string)
+	pass $test
+    }
+}
+
+if { $main_length == "" } {
+    # Bail out here, because we can't do the following tests if
+    # $main_length is unknown.
+    return -1
+}
+
+# Compute the size of the last instruction.
+
+set test "x/2i main+$main_length"
+gdb_test_multiple $test $test {
+    -re ".*($hex) <main\\+$main_length>:\[^\r\n\]+\r\n\[ \]+($hex).*\.\r\n$gdb_prompt $" {
+	set start $expect_out(1,string)
+	set end $expect_out(2,string)
+
+	set main_length [expr $main_length + $end - $start]
+	pass $test
+    }
+}
+
+if { $main_length == "" } {
+    # Bail out here, because we can't do the following tests if
+    # $main_length is unknown.
+    return -1
+}
+
+gdb_exit
+
 # Create the DWARF.
 set asm_file [standard_output_file $srcfile2]
 Dwarf::assemble $asm_file {
     declare_labels partial_label int_label int_label2
+    global main_length
 
     extern main
 
@@ -34,7 +80,7 @@ Dwarf::assemble $asm_file {
 	    subprogram {
 		{name main}
 		{low_pc main addr}
-		{high_pc "main + 10" addr}
+		{high_pc "main + $main_length" addr}
 	    }
 	}
     }
@@ -82,11 +128,17 @@ Dwarf::assemble $asm_file {
     }
 }
 
-if { [prepare_for_testing ${testfile}.exp ${testfile} \
+if  {[gdb_compile $asm_file ${binfile}2.o object {nodebug}] != ""} {
-	  [list $srcfile $asm_file] {nodebug}] } {
     return -1
 }
 
+if  {[gdb_compile [list ${binfile}1.o ${binfile}2.o] \
+	  "${binfile}" executable {}] != ""} {
+    return -1
+}
+
+clean_restart ${testfile}
+
 if ![runto_main] {
     return -1
 }