runtime: fix windows/arm signal handling assembly

Bug introduced in CL 288799: R12 is used but not set.

Fixes windows/arm builder.

Change-Id: I015a5a83cfa3bdd23da1ffb73713623764f2f817
Reviewed-on: https://go-review.googlesource.com/c/go/+/295109
Trust: Russ Cox <rsc@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

diff --git a/src/runtime/sys_windows_arm.s b/src/runtime/sys_windows_arm.s
index cd230ccffd42b6e6958a366a75594e48d87e56cb..4be5ce7da0c925d22b0e196a9620b6bee50128db 100644 (file)
--- a/src/runtime/sys_windows_arm.s
+++ b/src/runtime/sys_windows_arm.s
@@ -160,6 +160,11 @@ g0:
        BL      (R7)            // Call the go routine
        MOVW    16(R13), R4     // Fetch return value from stack
 
+       // Save system stack pointer for sigresume setup below.
+       // The exact value does not matter - nothing is read or written
+       // from this address. It just needs to be on the system stack.
+       MOVW    R13, R12
+
        // switch back to original stack and g
        MOVW    24(R13), R13
        MOVW    20(R13), g