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.
diff --git a/vm/mterp/out/InterpC-allstubs.c b/vm/mterp/out/InterpC-allstubs.c
index 04d7c32..0ca466b 100644
--- a/vm/mterp/out/InterpC-allstubs.c
+++ b/vm/mterp/out/InterpC-allstubs.c
@@ -302,6 +302,11 @@
#define INST_INST(_inst) ((_inst) & 0xff)
/*
+ * Replace the opcode (used when handling breakpoints). _opcode is a u1.
+ */
+#define INST_REPLACE_OP(_inst, _opcode) (((_inst) & 0xff00) | _opcode)
+
+/*
* Extract the "vA, vB" 4-bit registers from the instruction word (_inst is u2).
*/
#define INST_A(_inst) (((_inst) >> 8) & 0x0f)
@@ -2783,8 +2788,35 @@
HANDLE_OPCODE(OP_UNUSED_EB)
OP_END
-/* File: c/OP_UNUSED_EC.c */
-HANDLE_OPCODE(OP_UNUSED_EC)
+/* File: c/OP_BREAKPOINT.c */
+HANDLE_OPCODE(OP_BREAKPOINT)
+#if (INTERP_TYPE == INTERP_DBG) && defined(WITH_DEBUGGER)
+ {
+ /*
+ * Restart this instruction with the original opcode. We do
+ * this by simply jumping to the handler.
+ *
+ * It's probably not necessary to update "inst", but we do it
+ * for the sake of anything that needs to do disambiguation in a
+ * common handler with INST_INST.
+ *
+ * The breakpoint itself is handled over in updateDebugger(),
+ * because we need to detect other events (method entry, single
+ * step) and report them in the same event packet, and we're not
+ * yet handling those through breakpoint instructions. By the
+ * time we get here, the breakpoint has already been handled and
+ * the thread resumed.
+ */
+ u1 originalOpCode = dvmGetOriginalOpCode(pc);
+ LOGV("+++ break 0x%02x (0x%04x -> 0x%04x)\n", originalOpCode, inst,
+ INST_REPLACE_OP(inst, originalOpCode));
+ inst = INST_REPLACE_OP(inst, originalOpCode);
+ FINISH_BKPT(originalOpCode);
+ }
+#else
+ LOGE("Breakpoint hit in non-debug interpreter\n");
+ dvmAbort();
+#endif
OP_END
/* File: c/OP_THROW_VERIFICATION_ERROR.c */