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From 293b84bef3f6656a263248ff00c9d2fb82f4168d Mon Sep 17 00:00:00 2001
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Thu, 3 Dec 2020 13:29:58 +0100
Subject: [PATCH 1/2] runtime: allow builtin write function to be redirected
with function pointer
The x/sys/windows package currently uses go:linkname for other facilities
inside of runtime that are not suitable to be exposed as a public API
due to their dangers but are still necessary for manipulating any
low-level plumbing that the runtime controls.
Logging, via the built-in println and panic handler, is one such
low-level plumbing feature. In this case, x/sys/windows/svc needs to be
able to redirect panics to the Windows event log. Because the event log
is a complicated interface, this requires a bit more fiddling than the
simple solution used on Android (baking it into runtime itself), and
because Windows services are very diverse, the event log might not even
always be a desirable destination.
This commit accomplishes this by exposing a function pointer called
"overrideWrite" that low-level runtime packages like x/sys/windows/svc
can use to redirect output logs toward the event log or otherwise.
It is not safe or acceptable to use as a generic mechanism, and for that
reason, we wouldn't want to expose this as a real stable API, similar to
the other instances of go:linkname in x/sys/windows. But for packages
that must interoperate with low-level Go runtime fundamentals, this is a
safety hatch for packages that are developed in tandem with the runtime.
x/sys/windows is one such package.
Fixes #42888.
Change-Id: I77a32ff7e1494324e8cc38e792e007f86d32672d
---
src/runtime/time_nofake.go | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/src/runtime/time_nofake.go b/src/runtime/time_nofake.go
index 1912a94e87..0564448b2e 100644
--- a/src/runtime/time_nofake.go
+++ b/src/runtime/time_nofake.go
@@ -23,9 +23,14 @@ func walltime() (sec int64, nsec int32) {
return walltime1()
}
+var overrideWrite func(fd uintptr, p unsafe.Pointer, n int32) int32
+
// write must be nosplit on Windows (see write1)
//
//go:nosplit
func write(fd uintptr, p unsafe.Pointer, n int32) int32 {
+ if overrideWrite != nil {
+ return overrideWrite(fd, noescape(p), n)
+ }
return write1(fd, p, n)
}
--
2.29.2
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