[PATCH] Harden gdb.base/bp-permanent.exp

[Luis Machado <lgustavo at codesourcery dot com>]

This testcase does not work as expected in QEMU (aarch64 QEMU in my 
case). It fails when trying to manually write the breakpoint instruction 
to a certain PC address.

(gdb) p /x addr_bp[0] = buffer[0]^M
Cannot access memory at address 0x400834^M
(gdb) PASS: gdb.base/bp-permanent.exp: always_inserted=off, 
sw_watchpoint=0: setup: p /x addr_bp[0] = buffer[0]
p /x addr_bp[1] = buffer[1]^M
Cannot access memory at address 0x400835^M
(gdb) PASS: gdb.base/bp-permanent.exp: always_inserted=off, 
sw_watchpoint=0: setup: p /x addr_bp[1] = buffer[1]
p /x addr_bp[2] = buffer[2]^M
Cannot access memory at address 0x400836^M
(gdb) PASS: gdb.base/bp-permanent.exp: always_inserted=off, 
sw_watchpoint=0: setup: p /x addr_bp[2] = buffer[2]
p /x addr_bp[3] = buffer[3]^M
Cannot access memory at address 0x400837^M
(gdb) PASS: gdb.base/bp-permanent.exp: always_inserted=off, 
sw_watchpoint=0: setup: p /x addr_bp[3] = buffer[3]

The following patch prevents a number of failures by detecting this and 
bailing out in case the target has such a restriction. Writing to .text 
from within the program isn't any better. It just leads to a SIGSEGV.

Before the patch:

                === gdb Summary ===

# of expected passes            66
# of unexpected failures        56

After the patch:

                === gdb Summary ===

# of expected passes            26
# of unsupported tests          4

I regtested this on x86-64 and it still works fine.

Ok?

2015-04-09  Luis Machado  <lgustavo@codesourcery.com>

	gdb/testsuite/
	* gdb.base/bp-permanent.exp (test): Handle the case of being unable
	to write to the .text section.

diff --git a/gdb/testsuite/gdb.base/bp-permanent.exp b/gdb/testsuite/gdb.base/bp-permanent.exp
index 81a5293..9193db8 100644
--- a/gdb/testsuite/gdb.base/bp-permanent.exp
+++ b/gdb/testsuite/gdb.base/bp-permanent.exp
@@ -104,7 +104,18 @@ proc test {always_inserted sw_watchpoint} {
 	# to memory manually.
 	set count [expr $address_after_bp - $address_bp]
 	for {set i 0} {$i < $count} {incr i} {
-	    gdb_test "p /x addr_bp\[$i\] = buffer\[$i\]" " = .*"
+	    gdb_test_multiple "p /x addr_bp\[$i\] = buffer\[$i\]" $test {
+		-re "Cannot access memory at address $hex.*$gdb_prompt $" {
+		    # Some targets (QEMU for one) do not allow writes to the
+		    # .text section.  It is no use continuing with the test
+		    # at this point. Just return.
+		    unsupported $test
+		    return
+		}
+		-re " = .*$gdb_prompt $" {
+		    pass $test
+		}
+	    }
 	}
     }