go-patches: return correct nanosec param on arm64

Signed-off-by: Jason A. Donenfeld <[email protected]>

Author: zx2c4

go-patches/0004-runtime-use-correct-constant-when-computing-nsec-rem.patch

@@ -0,0 +1,81 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: "Jason A. Donenfeld" <[email protected]>
+Date: Fri, 5 Nov 2021 00:10:31 +0100
+Subject: [PATCH] runtime: use correct constant when computing nsec remainder
+
+A code comment on amd64 for windows and plan9 contained a snippet for
+splitting apart the sec and nsec components of a unix timestamp, with
+produced assembly below, which was then cleaned up by hand. When arm64
+was ported, that code snippet in the comment went through the compiler
+to produce some code that was then pasted and cleaned up. Unfortunately,
+the comment had a typo in it, containing 8 zeros instead of 9.
+
+This resulted in the constant used in the assembly being wrong, spotted
+by @bufflig's eagle eyes. So, this commit fixes the comment on all three
+platforms, and the assembly on windows/arm64.
+
+Fixes #48072.
+
+Change-Id: I786fe89147328b0d25544f52c927ddfdb9f6f1cf
+Reviewed-on: https://go-review.googlesource.com/c/go/+/361474
+Trust: Jason A. Donenfeld <[email protected]>
+Run-TryBot: Jason A. Donenfeld <[email protected]>
+Reviewed-by: Patrik Nyblom <[email protected]>
+TryBot-Result: Go Bot <[email protected]>
+---
+ src/runtime/sys_plan9_amd64.s    | 2 +-
+ src/runtime/time_windows_amd64.s | 2 +-
+ src/runtime/time_windows_arm64.s | 9 +++------
+ 3 files changed, 5 insertions(+), 8 deletions(-)
+
+diff --git a/src/runtime/sys_plan9_amd64.s b/src/runtime/sys_plan9_amd64.s
+index 731306ab44..068200b7f3 100644
+--- a/src/runtime/sys_plan9_amd64.s
++++ b/src/runtime/sys_plan9_amd64.s
+@@ -94,7 +94,7 @@ TEXT runtime·walltime(SB),NOSPLIT,$8-12
+ 	MOVQ	0(SP), AX
+ 
+ 	// generated code for
+-	//	func f(x uint64) (uint64, uint64) { return x/1000000000, x%100000000 }
++	//	func f(x uint64) (uint64, uint64) { return x/1000000000, x%1000000000 }
+ 	// adapted to reduce duplication
+ 	MOVQ	AX, CX
+ 	MOVQ	$1360296554856532783, AX
+diff --git a/src/runtime/time_windows_amd64.s b/src/runtime/time_windows_amd64.s
+index 045f64eb46..70f6a008cd 100644
+--- a/src/runtime/time_windows_amd64.s
++++ b/src/runtime/time_windows_amd64.s
+@@ -25,7 +25,7 @@ TEXT time·now(SB),NOSPLIT,$0-24
+ 	IMULQ	$100, AX
+ 
+ 	// generated code for
+-	//	func f(x uint64) (uint64, uint64) { return x/1000000000, x%100000000 }
++	//	func f(x uint64) (uint64, uint64) { return x/1000000000, x%1000000000 }
+ 	// adapted to reduce duplication
+ 	MOVQ	AX, CX
+ 	MOVQ	$1360296554856532783, AX
+diff --git a/src/runtime/time_windows_arm64.s b/src/runtime/time_windows_arm64.s
+index e8a0eb2f93..ef5b848473 100644
+--- a/src/runtime/time_windows_arm64.s
++++ b/src/runtime/time_windows_arm64.s
+@@ -32,17 +32,14 @@ TEXT time·now(SB),NOSPLIT|NOFRAME,$0-24
+ 	// Code stolen from compiler output for:
+ 	//
+ 	//	var x uint64
+-	//	func f() (sec uint64, nsec uint32) { return x / 1000000000, uint32(x % 100000000) }
++	//	func f() (sec uint64, nsec uint32) { return x / 1000000000, uint32(x % 1000000000) }
+ 	//
+ 	LSR	$1, R0, R1
+ 	MOVD	$-8543223759426509416, R2
+-	UMULH	R2, R1, R1
++	UMULH	R1, R2, R1
+ 	LSR	$28, R1, R1
+ 	MOVD	R1, sec+0(FP)
+-	MOVD	$-6067343680855748867, R1
+-	UMULH	R0, R1, R1
+-	LSR	$26, R1, R1
+-	MOVD	$100000000, R2
++	MOVD	$1000000000, R2
+ 	MSUB	R1, R0, R2, R0
+ 	MOVW	R0, nsec+8(FP)
+ 	RET