runtime: fix windows/arm64 callbackasm1 for frame pointer hack

Fixes the previously failing TestStdcallAndCDeclCallbacks
for the 9+ argument case.

The last time this code passed, the invisible frame pointer
below SP was apparently not enabled on windows/arm64.

Change-Id: Ifc3064e894b2f39d6410f3be51c17309ebab08a4
Reviewed-on: https://go-review.googlesource.com/c/go/+/312042
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

diff --git a/src/runtime/sys_windows_arm64.s b/src/runtime/sys_windows_arm64.s
index 6b28a0c2ef360d6804291c6cd8c64e82fe80a4a4..9fce9a8158fea8a90b5d61b5de261ca76d1d5aae 100644 (file)
--- a/src/runtime/sys_windows_arm64.s
+++ b/src/runtime/sys_windows_arm64.s
@@ -309,14 +309,19 @@ TEXT runtime·callbackasm1<ABIInternal>(SB),NOSPLIT,$208-0
 
        // Save callback register arguments R0-R7.
        // We do this at the top of the frame so they're contiguous with stack arguments.
-       MOVD    R0, arg0-(8*8)(SP)
-       MOVD    R1, arg1-(7*8)(SP)
-       MOVD    R2, arg2-(6*8)(SP)
-       MOVD    R3, arg3-(5*8)(SP)
-       MOVD    R4, arg4-(4*8)(SP)
-       MOVD    R5, arg5-(3*8)(SP)
-       MOVD    R6, arg6-(2*8)(SP)
-       MOVD    R7, arg7-(1*8)(SP)
+       // The 7*8 setting up R14 looks like a bug but is not: the eighth word
+       // is the space the assembler reserved for our caller's frame pointer,
+       // but we are not called from Go so that space is ours to use,
+       // and we must to be contiguous with the stack arguments.
+       MOVD    $arg0-(7*8)(SP), R14
+       MOVD    R0, (0*8)(R14)
+       MOVD    R1, (1*8)(R14)
+       MOVD    R2, (2*8)(R14)
+       MOVD    R3, (3*8)(R14)
+       MOVD    R4, (4*8)(R14)
+       MOVD    R5, (5*8)(R14)
+       MOVD    R6, (6*8)(R14)
+       MOVD    R7, (7*8)(R14)
 
        // Push C callee-save registers R19-R28.
        // LR, FP already saved.
@@ -325,7 +330,7 @@ TEXT runtime·callbackasm1<ABIInternal>(SB),NOSPLIT,$208-0
        // Create a struct callbackArgs on our stack.
        MOVD    $cbargs-(18*8+callbackArgs__size)(SP), R13
        MOVD    R12, callbackArgs_index(R13)    // callback index
-       MOVD    $arg0-(8*8)(SP), R0
+       MOVD    R14, R0
        MOVD    R0, callbackArgs_args(R13)              // address of args vector
        MOVD    $0, R0
        MOVD    R0, callbackArgs_result(R13)    // result