Change the way breakpoints work.

This replaces the breakpoint mechanism with a more efficient approach.
We now insert breakpoint instructions into the bytecode stream instead of
maintaining a table.  This requires mapping DEX files as private instead
of shared, which allows copy-on-write to work.  mprotect() is used to
guard the pages against inadvertent writes.

Unused opcode EC is now OP_BREAKPOINT.  It's not recognized by dexdump or
any interpreter except portdbg, but it can be encountered by the bytecode
verifier (the debugger can request breakpoints in unverified code).
Breakpoint changes are blocked while the verifier runs to avoid races.

This eliminates method->debugBreakpointCount, which is no longer needed.
(Also, it clashed with LinearAlloc's read-only mode.)

The deferred verification error mechanism was using a code-copying
approach to modify the bytecode stream.  That has been changed to use
the same copy-on-write modification mechanism.

Also, normalized all PAGE_SIZE/PAGESIZE references to a single
SYSTEM_PAGE_SIZE define.

Simple Fibonacci computation test times (opal-eng):
  JIT, no debugger: 10.6ms
  Fast interp, no debugger: 36ms
  Portable interp, no debugger: 43.8ms

  ORIG debug interp, no breakpoints set: 458ms
  ORIG debug interp, breakpoint set nearby: 697ms

  NEW debug interp, no breakpoints set: 341ms
  NEW debug interp, breakpoints set nearby: 341ms

Where "nearby" means there's a breakpoint in the method doing the
computation that isn't actually hit -- the VM had an optimization where
it flagged methods with breakpoints and skipped some of the processing
when possible.

The bottom line is that code should run noticeably faster while a
debugger is attached.

1 files changed, 16 insertions, 0 deletions

diff --git a/vm/DvmDex.h b/vm/DvmDex.h
index be31af37d..9f3903aee 100644
--- a/vm/DvmDex.h
+++ b/vm/DvmDex.h
@@ -13,6 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 /*
  * The VM wraps some additional data structures around the DexFile.  These
  * are defined here.
@@ -81,6 +82,21 @@ int dvmDexFileOpenPartial(const void* addr, int len, DvmDex** ppDvmDex);
 void dvmDexFileFree(DvmDex* pDvmDex);
 
 
+/*
+ * Change the 1- or 2-byte value at the specified address to a new value.  If
+ * the location already has the new value, do nothing.
+ *
+ * This does not make any synchronization guarantees.  The caller must
+ * ensure exclusivity vs. other callers.
+ *
+ * For the 2-byte call, the pointer should have 16-bit alignment.
+ *
+ * Returns "true" on success.
+ */
+bool dvmDexChangeDex1(DvmDex* pDvmDex, u1* addr, u1 newVal);
+bool dvmDexChangeDex2(DvmDex* pDvmDex, u2* addr, u2 newVal);
+
+
 #if DVM_RESOLVER_CACHE == DVM_RC_DISABLED
 /* 1:1 mapping */