[arm64] Support passing more than eight arguments to C functions

src/arm64/macro-assembler-arm64.cc

Index: src/arm64/macro-assembler-arm64.cc
diff --git a/src/arm64/macro-assembler-arm64.cc b/src/arm64/macro-assembler-arm64.cc
index 5edcd7b0449bff8457356c544eef0456b587b7b5..8cdfa5d9efe6e03a1f9c9a504d50bbf12ce646cd 100644
--- a/src/arm64/macro-assembler-arm64.cc
+++ b/src/arm64/macro-assembler-arm64.cc
@@ -1791,14 +1791,12 @@ void MacroAssembler::CallCFunction(ExternalReference function,
   CallCFunction(temp, num_of_reg_args, num_of_double_args);
 }
 
+static const int kRegisterPassedArguments = 8;
 
 void MacroAssembler::CallCFunction(Register function,
                                    int num_of_reg_args,
                                    int num_of_double_args) {
   DCHECK(has_frame());
-  // We can pass 8 integer arguments in registers. If we need to pass more than
-  // that, we'll need to implement support for passing them on the stack.
-  DCHECK(num_of_reg_args <= 8);
 
   // If we're passing doubles, we're limited to the following prototypes
   // (defined by ExternalReference::Type):
@@ -1811,6 +1809,10 @@ void MacroAssembler::CallCFunction(Register function,
     DCHECK((num_of_double_args + num_of_reg_args) <= 2);
   }
 
+  // We rely on the frame alignment being 16 bytes, which means we never need
+  // to align the CSP by an unknown number of bytes and we always know the delta
+  // between the stack pointer and the frame pointer.
+  DCHECK(ActivationFrameAlignment() == 16);
 
   // If the stack pointer is not csp, we need to derive an aligned csp from the
   // current stack pointer.
@@ -1819,16 +1821,18 @@ void MacroAssembler::CallCFunction(Register function,
     AssertStackConsistency();
 
     int sp_alignment = ActivationFrameAlignment();
-    // The ABI mandates at least 16-byte alignment.
-    DCHECK(sp_alignment >= 16);
-    DCHECK(base::bits::IsPowerOfTwo32(sp_alignment));
-
     // The current stack pointer is a callee saved register, and is preserved
     // across the call.
     DCHECK(kCalleeSaved.IncludesAliasOf(old_stack_pointer));
 
-    // Align and synchronize the system stack pointer with jssp.
-    Bic(csp, old_stack_pointer, sp_alignment - 1);
+    // If more than eight arguments are passed to the function, we expect the
+    // ninth argument onwards to have been placed on the csp-based stack
+    // already. We assume csp already points to the last stack-passed argument
+    // in that case.
+    // Otherwise, align and synchronize the system stack pointer with jssp.
+    if (num_of_reg_args <= kRegisterPassedArguments) {
+      Bic(csp, old_stack_pointer, sp_alignment - 1);
+    }
     SetStackPointer(csp);
   }
 
@@ -1836,19 +1840,39 @@ void MacroAssembler::CallCFunction(Register function,
   // so the return address in the link register stays correct.
   Call(function);
 
-  if (!csp.Is(old_stack_pointer)) {
+  if (csp.Is(old_stack_pointer)) {
+    if (num_of_reg_args > kRegisterPassedArguments) {
+      // Drop the register passed arguments.
+      int claim_slots = RoundUp(num_of_reg_args - kRegisterPassedArguments, 2);
+      Drop(claim_slots);
+    }
+  } else {
+    DCHECK(jssp.Is(old_stack_pointer));
     if (emit_debug_code()) {
-      // Because the stack pointer must be aligned on a 16-byte boundary, the
-      // aligned csp can be up to 12 bytes below the jssp. This is the case
-      // where we only pushed one W register on top of an aligned jssp.
       UseScratchRegisterScope temps(this);
       Register temp = temps.AcquireX();
-      DCHECK(ActivationFrameAlignment() == 16);
-      Sub(temp, csp, old_stack_pointer);
-      // We want temp <= 0 && temp >= -12.
-      Cmp(temp, 0);
-      Ccmp(temp, -12, NFlag, le);
-      Check(ge, kTheStackWasCorruptedByMacroAssemblerCall);
+
+      if (num_of_reg_args > kRegisterPassedArguments) {
+        // We don't need to drop stack arguments, as the stack pointer will be
+        // jssp when returning from this function. However, in debug builds, we
+        // can check that jssp is as expected.
+        int claim_slots =
+            RoundUp(num_of_reg_args - kRegisterPassedArguments, 2);
+
+        // Check jssp matches the previous value on the stack.
+        Ldr(temp, MemOperand(csp, claim_slots * kPointerSize));
+        Cmp(jssp, temp);
+        Check(eq, kTheStackWasCorruptedByMacroAssemblerCall);
+      } else {
+        // Because the stack pointer must be aligned on a 16-byte boundary, the
+        // aligned csp can be up to 12 bytes below the jssp. This is the case
+        // where we only pushed one W register on top of an aligned jssp.
+        Sub(temp, csp, old_stack_pointer);
+        // We want temp <= 0 && temp >= -12.
+        Cmp(temp, 0);
+        Ccmp(temp, -12, NFlag, le);
+        Check(ge, kTheStackWasCorruptedByMacroAssemblerCall);
+      }
     }
     SetStackPointer(old_stack_pointer);
   }