AArch64: Implicit StackOverflow/NPE/Suspend checks.
This implements implicit stack overflow checks and null pointer exceptions
for AArch64. Suspend checks are implemented but not switched on yet.
Change-Id: I2eb076f2c0c9d94793d5a898fea49cf409b4eb66
Signed-off-by: Stuart Monteith <stuart.monteith@arm.com>
diff --git a/runtime/arch/arm64/fault_handler_arm64.cc b/runtime/arch/arm64/fault_handler_arm64.cc
index 34eede6..dc82cc2 100644
--- a/runtime/arch/arm64/fault_handler_arm64.cc
+++ b/runtime/arch/arm64/fault_handler_arm64.cc
@@ -21,7 +21,15 @@
#include "globals.h"
#include "base/logging.h"
#include "base/hex_dump.h"
+#include "registers_arm64.h"
+#include "mirror/art_method.h"
+#include "mirror/art_method-inl.h"
+#include "thread.h"
+#include "thread-inl.h"
+extern "C" void art_quick_throw_stack_overflow_from_signal();
+extern "C" void art_quick_throw_null_pointer_exception();
+extern "C" void art_quick_implicit_suspend();
//
// ARM64 specific fault handler functions.
@@ -32,17 +40,160 @@
void FaultManager::GetMethodAndReturnPCAndSP(siginfo_t* siginfo, void* context,
mirror::ArtMethod** out_method,
uintptr_t* out_return_pc, uintptr_t* out_sp) {
+ struct ucontext *uc = reinterpret_cast<struct ucontext *>(context);
+ struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext);
+ *out_sp = static_cast<uintptr_t>(sc->sp);
+ VLOG(signals) << "sp: " << *out_sp;
+ if (*out_sp == 0) {
+ return;
+ }
+
+ // In the case of a stack overflow, the stack is not valid and we can't
+ // get the method from the top of the stack. However it's in x0.
+ uintptr_t* fault_addr = reinterpret_cast<uintptr_t*>(sc->fault_address);
+ uintptr_t* overflow_addr = reinterpret_cast<uintptr_t*>(
+ reinterpret_cast<uint8_t*>(*out_sp) - GetStackOverflowReservedBytes(kArm64));
+ if (overflow_addr == fault_addr) {
+ *out_method = reinterpret_cast<mirror::ArtMethod*>(sc->regs[0]);
+ } else {
+ // The method is at the top of the stack.
+ *out_method = (reinterpret_cast<StackReference<mirror::ArtMethod>* >(*out_sp)[0]).AsMirrorPtr();
+ }
+
+ // Work out the return PC. This will be the address of the instruction
+ // following the faulting ldr/str instruction.
+ VLOG(signals) << "pc: " << std::hex
+ << static_cast<void*>(reinterpret_cast<uint8_t*>(sc->pc));
+
+ *out_return_pc = sc->pc + 4;
}
bool NullPointerHandler::Action(int sig, siginfo_t* info, void* context) {
- return false;
+ // The code that looks for the catch location needs to know the value of the
+ // PC at the point of call. For Null checks we insert a GC map that is immediately after
+ // the load/store instruction that might cause the fault.
+
+ struct ucontext *uc = reinterpret_cast<struct ucontext*>(context);
+ struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext);
+
+ sc->regs[30] = sc->pc + 4; // LR needs to point to gc map location
+
+ sc->pc = reinterpret_cast<uintptr_t>(art_quick_throw_null_pointer_exception);
+ VLOG(signals) << "Generating null pointer exception";
+ return true;
}
+// A suspend check is done using the following instruction sequence:
+// 0xf7223228: f9405640 ldr x0, [x18, #168]
+// .. some intervening instructions
+// 0xf7223230: f9400000 ldr x0, [x0]
+
+// The offset from r18 is Thread::ThreadSuspendTriggerOffset().
+// To check for a suspend check, we examine the instructions that caused
+// the fault (at PC-4 and PC).
bool SuspensionHandler::Action(int sig, siginfo_t* info, void* context) {
+ // These are the instructions to check for. The first one is the ldr x0,[r18,#xxx]
+ // where xxx is the offset of the suspend trigger.
+ uint32_t checkinst1 = 0xf9400240 | (Thread::ThreadSuspendTriggerOffset<8>().Int32Value() << 7);
+ uint32_t checkinst2 = 0xf9400000;
+
+ struct ucontext *uc = reinterpret_cast<struct ucontext *>(context);
+ struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext);
+ uint8_t* ptr2 = reinterpret_cast<uint8_t*>(sc->pc);
+ uint8_t* ptr1 = ptr2 - 4;
+ VLOG(signals) << "checking suspend";
+
+ uint32_t inst2 = *reinterpret_cast<uint32_t*>(ptr2);
+ VLOG(signals) << "inst2: " << std::hex << inst2 << " checkinst2: " << checkinst2;
+ if (inst2 != checkinst2) {
+ // Second instruction is not good, not ours.
+ return false;
+ }
+
+ // The first instruction can a little bit up the stream due to load hoisting
+ // in the compiler.
+ uint8_t* limit = ptr1 - 80; // Compiler will hoist to a max of 20 instructions.
+ bool found = false;
+ while (ptr1 > limit) {
+ uint32_t inst1 = *reinterpret_cast<uint32_t*>(ptr1);
+ VLOG(signals) << "inst1: " << std::hex << inst1 << " checkinst1: " << checkinst1;
+ if (inst1 == checkinst1) {
+ found = true;
+ break;
+ }
+ ptr1 -= 4;
+ }
+ if (found) {
+ VLOG(signals) << "suspend check match";
+ // This is a suspend check. Arrange for the signal handler to return to
+ // art_quick_implicit_suspend. Also set LR so that after the suspend check it
+ // will resume the instruction (current PC + 4). PC points to the
+ // ldr x0,[x0,#0] instruction (r0 will be 0, set by the trigger).
+
+ sc->regs[30] = sc->pc + 4;
+ sc->pc = reinterpret_cast<uintptr_t>(art_quick_implicit_suspend);
+
+ // Now remove the suspend trigger that caused this fault.
+ Thread::Current()->RemoveSuspendTrigger();
+ VLOG(signals) << "removed suspend trigger invoking test suspend";
+ return true;
+ }
return false;
}
bool StackOverflowHandler::Action(int sig, siginfo_t* info, void* context) {
- return false;
+ struct ucontext *uc = reinterpret_cast<struct ucontext *>(context);
+ struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext);
+ VLOG(signals) << "stack overflow handler with sp at " << std::hex << &uc;
+ VLOG(signals) << "sigcontext: " << std::hex << sc;
+
+ uintptr_t sp = sc->sp;
+ VLOG(signals) << "sp: " << std::hex << sp;
+
+ uintptr_t fault_addr = sc->fault_address;
+ VLOG(signals) << "fault_addr: " << std::hex << fault_addr;
+ VLOG(signals) << "checking for stack overflow, sp: " << std::hex << sp <<
+ ", fault_addr: " << fault_addr;
+
+ uintptr_t overflow_addr = sp - GetStackOverflowReservedBytes(kArm64);
+
+ Thread* self = reinterpret_cast<Thread*>(sc->regs[art::arm64::TR]);
+ CHECK_EQ(self, Thread::Current());
+ uintptr_t pregion = reinterpret_cast<uintptr_t>(self->GetStackEnd()) -
+ Thread::kStackOverflowProtectedSize;
+
+ // Check that the fault address is the value expected for a stack overflow.
+ if (fault_addr != overflow_addr) {
+ VLOG(signals) << "Not a stack overflow";
+ return false;
+ }
+
+ // We know this is a stack overflow. We need to move the sp to the overflow region
+ // that exists below the protected region. Determine the address of the next
+ // available valid address below the protected region.
+ uintptr_t prevsp = sp;
+ sp = pregion;
+ VLOG(signals) << "setting sp to overflow region at " << std::hex << sp;
+
+ // Since the compiler puts the implicit overflow
+ // check before the callee save instructions, the SP is already pointing to
+ // the previous frame.
+ VLOG(signals) << "previous frame: " << std::hex << prevsp;
+
+ // Now establish the stack pointer for the signal return.
+ sc->sp = prevsp;
+
+ // Tell the stack overflow code where the new stack pointer should be.
+ sc->regs[art::arm64::IP0] = sp; // aka x16
+
+ // Now arrange for the signal handler to return to art_quick_throw_stack_overflow_from_signal.
+ // The value of LR must be the same as it was when we entered the code that
+ // caused this fault. This will be inserted into a callee save frame by
+ // the function to which this handler returns (art_quick_throw_stack_overflow_from_signal).
+ sc->pc = reinterpret_cast<uintptr_t>(art_quick_throw_stack_overflow_from_signal);
+
+ // The kernel will now return to the address in sc->pc.
+ return true;
}
} // namespace art
+
diff --git a/runtime/arch/arm64/quick_entrypoints_arm64.S b/runtime/arch/arm64/quick_entrypoints_arm64.S
index ba85d32..04be4a2 100644
--- a/runtime/arch/arm64/quick_entrypoints_arm64.S
+++ b/runtime/arch/arm64/quick_entrypoints_arm64.S
@@ -435,6 +435,31 @@
*/
ONE_ARG_RUNTIME_EXCEPTION art_quick_throw_no_such_method, artThrowNoSuchMethodFromCode
+ /*
+ * Invoke stack overflow exception from signal handler.
+ * On entry:
+ * xSELF: thread
+ * SP: address of last known frame
+ * IP0: address of next valid SP below protected region in stack
+ *
+ * This is deceptively simple but hides some complexity. It is called in the case of
+ * a stack overflow condition during implicit checks. The signal handler has been
+ * called by the kernel due to a load from the protected stack region. The handler
+ * works out the address of the previous frame and passes this in SP. However there
+ * is a piece of memory somewhere below the current SP that is not accessible (the
+ * memory that caused the signal). The signal handler works out the next
+ * accessible value of SP and passes this in x16/IP0. This code then sets up the SP
+ * to be this new value and calls the code to create and throw the stack overflow
+ * exception.
+ */
+ENTRY art_quick_throw_stack_overflow_from_signal
+ SETUP_SAVE_ALL_CALLEE_SAVE_FRAME // save all registers as basis for long jump context
+ mov x0, xSELF // pass Thread::Current
+ mov x1, sp // pass SP
+ mov sp, xIP0 // move SP down to below protected region.
+ b artThrowStackOverflowFromCode // artThrowStackOverflowFromCode(Thread*, SP)
+END art_quick_throw_stack_overflow_from_signal
+
/*
* All generated callsites for interface invokes and invocation slow paths will load arguments
* as usual - except instead of loading arg0/x0 with the target Method*, arg0/x0 will contain
@@ -1323,6 +1348,14 @@
RESTORE_REF_ONLY_CALLEE_SAVE_FRAME_AND_RETURN
END art_quick_test_suspend
+ENTRY art_quick_implicit_suspend
+ mov x0, xSELF
+ SETUP_REF_ONLY_CALLEE_SAVE_FRAME // save callee saves for stack crawl
+ mov x1, sp
+ bl artTestSuspendFromCode // (Thread*, SP)
+ RESTORE_REF_ONLY_CALLEE_SAVE_FRAME_AND_RETURN
+END art_quick_implicit_suspend
+
/*
* Called by managed code that is attempting to call a method on a proxy class. On entry
* x0 holds the proxy method and x1 holds the receiver; The frame size of the invoked proxy
diff --git a/runtime/runtime.cc b/runtime/runtime.cc
index 2c25c2c..fe877d5 100644
--- a/runtime/runtime.cc
+++ b/runtime/runtime.cc
@@ -620,6 +620,7 @@
case kArm:
case kThumb2:
case kX86:
+ case kArm64:
implicit_null_checks_ = true;
implicit_so_checks_ = true;
break;