Remove duplicated code on checking address 0x0 is accessiable

I find some gdb.python tests fail on arm-none-eabi target, because the
tests assume that memory on address 0x is inaccessible.  Some tests
(in gdb.base) are aware of this, so do a "x 0" check first.  However,
the code is copy-n-paste.

This patch is to move the "x 0" check to a procedure in lib/gdb.exp,
and get needed tests call it.  The original code matches pattern
"0x0:\[ \t\]*Error accessing memory address 0x0\r\n$gdb_prompt $", but
I remove it from the new proc is_address_zero_readable, because GDB
doesn't emit such message any more.

gdb/testsuite:

2014-08-09  Yao Qi  <yao@codesourcery.com>

	* gdb.base/display.exp: Invoke is_address_zero_readable.
	* gdb.guile/scm-value.exp (test_value_in_inferior): Likewise.
	* gdb.python/py-value.exp (test_value_in_inferior): Likewise.
	* gdb.base/hbreak-unmapped.exp: Return if
	is_address_zero_readable returns true.
	* gdb.base/signest.exp: Likewise.
	* gdb.base/signull.exp: Likewise.
	* gdb.base/sigbpt.exp: Likewise.
	* gdb.guile/scm-disasm.exp: Do the test if
	is_address_zero_readable returns false.
	* gdb.guile/scm-pretty-print.exp (run_lang_tests): Likewise.
	* gdb.python/py-arch.exp: Likewise.
	* gdb.python/py-prettyprint.exp (run_lang_tests): Likewise.
	* lib/gdb.exp (is_address_zero_readable): New proc.

3 files changed, 9 insertions, 12 deletions

diff --git a/gdb/testsuite/gdb.guile/scm-disasm.exp b/gdb/testsuite/gdb.guile/scm-disasm.exp
index 5a1dae3..ccc0c88 100644
--- a/gdb/testsuite/gdb.guile/scm-disasm.exp
+++ b/gdb/testsuite/gdb.guile/scm-disasm.exp
@@ -83,9 +83,11 @@ gdb_test "guile (print (length insn-list4))" \
 
 test_disassemble_1 "basic" "pc" ""
 
-# Negative test
-gdb_test "guile (arch-disassemble arch 0 #:size 1)" \
-    "ERROR: Cannot access memory at address 0x.*" "test bad memory access"
+if { ![is_address_zero_readable] } {
+    # Negative test
+    gdb_test "guile (arch-disassemble arch 0 #:size 1)" \
+	"ERROR: Cannot access memory at address 0x.*" "test bad memory access"
+}
 
 # Test disassembly through a port.
 
diff --git a/gdb/testsuite/gdb.guile/scm-pretty-print.exp b/gdb/testsuite/gdb.guile/scm-pretty-print.exp
index 555d751..55a2393 100644
--- a/gdb/testsuite/gdb.guile/scm-pretty-print.exp
+++ b/gdb/testsuite/gdb.guile/scm-pretty-print.exp
@@ -81,7 +81,9 @@ proc run_lang_tests {exefile lang} {
 	gdb_scm_test_silent_cmd "set print elements 200" "" 1
     }
 
-    gdb_test "print ns2" "<error reading variable: ERROR: Cannot access memory at address 0x0>"
+    if { ![is_address_zero_readable] } {
+	gdb_test "print ns2" "<error reading variable: ERROR: Cannot access memory at address 0x0>"
+    }
 
     gdb_test "print x" " = \"this is x\""
     gdb_test "print cstring" " = \"const string\""
diff --git a/gdb/testsuite/gdb.guile/scm-value.exp b/gdb/testsuite/gdb.guile/scm-value.exp
index 425873e..91e1a56 100644
--- a/gdb/testsuite/gdb.guile/scm-value.exp
+++ b/gdb/testsuite/gdb.guile/scm-value.exp
@@ -105,14 +105,7 @@ proc test_value_in_inferior {} {
     # Test displaying a variable that is temporarily at a bad address.
     # But if we can examine what's at memory address 0, then we'll also be
     # able to display it without error.  Don't run the test in that case.
-    set can_read_0 0
-    gdb_test_multiple "x 0" "memory at address 0" {
-	-re "0x0:\[ \t\]*Cannot access memory at address 0x0\r\n$gdb_prompt $" { }
-	-re "0x0:\[ \t\]*Error accessing memory address 0x0\r\n$gdb_prompt $" { }
-	-re "\r\n$gdb_prompt $" {
-	    set can_read_0 1
-	}
-    }
+    set can_read_0 [is_address_zero_readable]
 
     # Test memory error.
     set test "parse_and_eval with memory error"