From: Michael Pratt <mpratt@google.com>
Date: Tue, 9 Nov 2021 16:35:52 +0000 (-0500)
Subject: runtime: add upper half and carry bit with zero
X-Git-Tag: go1.18beta1~436
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=15a54d627ca7a0bdf45a3d1862b35a892024cacc;p=gostls13.git

runtime: add upper half and carry bit with zero

https://golang.org/cl/246763 accidentally changed this from upper + 0 +
carry to upper + old vdsoSP + carry.

The old value of vdsoPC is usually zero, so this typically works.
However, the reentrant case will have a non-zero value, resulting in a
bogus returned time.

Fixes #49481

Change-Id: I0110b84277bf911804cb0ff8097aebf1b7eb100a
Reviewed-on: https://go-review.googlesource.com/c/go/+/362674
Trust: Michael Pratt <mpratt@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
---

diff --git a/src/runtime/sys_linux_arm.s b/src/runtime/sys_linux_arm.s
index 65935de99f..ca443b699f 100644
--- a/src/runtime/sys_linux_arm.s
+++ b/src/runtime/sys_linux_arm.s
@@ -456,7 +456,7 @@ finish:
 	MOVW	$1000000000, R3
 	MULLU	R0, R3, (R1, R0)
 	ADD.S	R2, R0
-	ADC	R4, R1
+	ADC	$0, R1	// Add carry bit to upper half.
 
 	MOVW	R0, ret_lo+0(FP)
 	MOVW	R1, ret_hi+4(FP)