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/analysis/CodeVerify.c b/vm/analysis/CodeVerify.c
index f945f23..911775c 100644
--- a/vm/analysis/CodeVerify.c
+++ b/vm/analysis/CodeVerify.c
@@ -2926,6 +2926,9 @@
* receive a "nop". The instruction's length will be left unchanged
* in "insnFlags".
*
+ * The verifier explicitly locks out breakpoint activity, so there should
+ * be no clashes with the debugger.
+ *
* IMPORTANT: this may replace meth->insns with a pointer to a new copy of
* the instructions.
*
@@ -2939,7 +2942,7 @@
u2 oldInsn = *oldInsns;
bool result = false;
- dvmMakeCodeReadWrite(meth);
+ //dvmMakeCodeReadWrite(meth);
//LOGD(" was 0x%04x\n", oldInsn);
u2* newInsns = (u2*) meth->insns + insnIdx;
@@ -3018,7 +3021,8 @@
/* nothing to do */
break;
case 3:
- newInsns[2] = OP_NOP;
+ dvmDexChangeDex2(meth->clazz->pDvmDex, newInsns+2, OP_NOP);
+ //newInsns[2] = OP_NOP;
break;
default:
/* whoops */
@@ -3028,13 +3032,15 @@
}
/* encode the opcode, with the failure code in the high byte */
- newInsns[0] = OP_THROW_VERIFICATION_ERROR |
+ u2 newVal = OP_THROW_VERIFICATION_ERROR |
(failure << 8) | (refType << (8 + kVerifyErrorRefTypeShift));
+ //newInsns[0] = newVal;
+ dvmDexChangeDex2(meth->clazz->pDvmDex, newInsns, newVal);
result = true;
bail:
- dvmMakeCodeReadOnly(meth);
+ //dvmMakeCodeReadOnly(meth);
return result;
}
@@ -5420,7 +5426,7 @@
failure = VERIFY_ERROR_GENERIC;
break;
- /* these should never appear */
+ /* these should never appear during verification */
case OP_UNUSED_3E:
case OP_UNUSED_3F:
case OP_UNUSED_40:
@@ -5439,7 +5445,7 @@
case OP_UNUSED_E9:
case OP_UNUSED_EA:
case OP_UNUSED_EB:
- case OP_UNUSED_EC:
+ case OP_BREAKPOINT:
case OP_UNUSED_EF:
case OP_UNUSED_F1:
case OP_UNUSED_FC: