Add support for debugging ART to the dalvik.gdb script.

This adds two commands:

art-on
art-off

To the gdbclient script for debugging ART-based executables in gdb.
The default is 'art-on'

Bug: 17409881
Change-Id: I90a1aed603e50853a40d5f5ec1c9b168dc17ddc7
(cherry picked from commit 22382a4774)

scripts/gdb/dalvik.gdb

@@ -49,3 +49,62 @@ document dbt
     frame. If omitted r5 will be used as the default (as the case in the
     interpreter and JIT'ed code).
 end
+
+# ART debugging.  ART uses SIGSEGV signals for internal purposes.  To allow
+# gdb to debug programs using ART we need to treat this signal specially.  We
+# also set a breakpoint in a libart.so function to stop when the program
+# hits an unexpected breakpoint
+set $art_debug_enabled = 0
+define art-on
+    if $art_debug_enabled == 0
+        # deal with SIGSEGV signals
+        handle SIGSEGV noprint nostop pass
+
+        # set a breakpoint and record its number
+        set breakpoint pending on
+        break art_sigsegv_fault
+        set $art_bpnum = $bpnum
+        commands $art_bpnum
+        silent
+        printf "Caught SIGSEGV in user program\n"
+        end
+        set breakpoint pending auto
+
+        printf "ART debugging mode is enabled.\n"
+        set $art_debug_enabled = 1
+    else
+        printf "ART debugging mode is already enabled.\n"
+    end
+end
+
+document art-on
+    Enter ART debugging mode. In ART debugging mode, SIGSEGV signals are ignored
+    by gdb unless they are not handled by ART itself.  A breakpoint is
+    set to stop the program when an unexpected SIGSEGV signal is
+    encountered.
+
+    To switch ART debugging mode off, use "art-off"
+end
+
+define art-off
+    if $art_debug_enabled == 1
+        # restore SIGSEGV to its default
+        handle SIGSEGV print stop pass
+
+        # delete our breakpoint
+        delete $art_bpnum
+
+        set $art_debug_enabled = 0
+        printf "ART debugging mode is disabled.\n"
+    end
+end
+
+document art-off
+    Leave ART debugging mode.  Signal handling is restored to default settings.
+
+    Use the command "art-on" to enable ART debugging mode.
+end
+
+# switch on ART debugging
+art-on
+