From 946351d5a27d7dc5550f579ddfec926790903fc5 Mon Sep 17 00:00:00 2001
From: Cherry Zhang <cherryyz@google.com>
Date: Tue, 2 Feb 2021 18:25:39 -0500
Subject: [PATCH] [dev.regabi] runtime: zero X15 in racecall

racecall can be called in ABIInternal context (e.g. raceread
calling racecalladdr calling racecall) without wrapper. racecall
calls C code, which doesn't preserve our special registers. Set
them explicitly in racecall upon returning from C.

Change-Id: Ic990479c1fca6bb8a3b151325c7a89be8331a530
Reviewed-on: https://go-review.googlesource.com/c/go/+/289709
Trust: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Jeremy Faller <jeremy@golang.org>
---
 src/runtime/race_amd64.s | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/runtime/race_amd64.s b/src/runtime/race_amd64.s
index cf0a51462fd..fd41b5690a6 100644
--- a/src/runtime/race_amd64.s
+++ b/src/runtime/race_amd64.s
@@ -412,6 +412,9 @@ call:
 	ANDQ	$~15, SP	// alignment for gcc ABI
 	CALL	AX
 	MOVQ	R12, SP
+	// Back to Go world, set special registers.
+	// The g register (R14) is preserved in C.
+	XORPS	X15, X15
 	RET
 
 // C->Go callback thunk that allows to call runtime·racesymbolize from C code.