From 901bf291bc90819cb6dad76064475cf9ecbc9651 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Thu, 3 Dec 2020 13:29:58 +0100 Subject: [PATCH] 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. Updates #42888. Change-Id: I77a32ff7e1494324e8cc38e792e007f86d32672d Reviewed-on: https://go-review.googlesource.com/c/go/+/278792 Trust: Jason A. Donenfeld Run-TryBot: Jason A. Donenfeld TryBot-Result: Go Bot Reviewed-by: Russ Cox --- 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 2b85c5aa01..70a2102b22 100644 --- a/src/runtime/time_nofake.go +++ b/src/runtime/time_nofake.go @@ -19,9 +19,14 @@ func nanotime() int64 { return nanotime1() } +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) } -- 2.50.0