From c33d45a898ab1d966faba33d18acdffefb0fae0d Mon Sep 17 00:00:00 2001 From: Matthew Dempsky Date: Thu, 3 Oct 2019 10:49:28 -0700 Subject: [PATCH] cmd/compile: don't statically copy string-typed variables During package initialization, the compiler tries to optimize: var A = "foo" var B = A into var A = "foo" var B = "foo" so that we can statically initialize both A and B and skip emitting dynamic initialization code to assign "B = A". However, this isn't safe in the presence of cmd/link's -X flag, which might overwrite an initialized string-typed variable at link time. In particular, if cmd/link changes A's static initialization, it won't know it also needs to change B's static initialization. To address this, this CL disables this optimization for string-typed variables. Fixes #34675. Change-Id: I1c18f3b855f6d7114aeb39f96aaaf1b452b88236 Reviewed-on: https://go-review.googlesource.com/c/go/+/198657 Run-TryBot: Matthew Dempsky Reviewed-by: Cuong Manh Le Reviewed-by: Brad Fitzpatrick TryBot-Result: Gobot Gobot --- src/cmd/compile/internal/gc/sinit.go | 3 +++ test/linkx.go | 9 +++++++++ test/linkx_run.go | 2 +- 3 files changed, 13 insertions(+), 1 deletion(-) diff --git a/src/cmd/compile/internal/gc/sinit.go b/src/cmd/compile/internal/gc/sinit.go index ae16d41b1c..a6d13d1ac5 100644 --- a/src/cmd/compile/internal/gc/sinit.go +++ b/src/cmd/compile/internal/gc/sinit.go @@ -83,6 +83,9 @@ func (s *InitSchedule) staticcopy(l *Node, r *Node) bool { if r.Name.Defn.Op != OAS { return false } + if r.Type.IsString() { // perhaps overwritten by cmd/link -X (#34675) + return false + } orig := r r = r.Name.Defn.Right diff --git a/test/linkx.go b/test/linkx.go index 20b8c773d8..520a065182 100644 --- a/test/linkx.go +++ b/test/linkx.go @@ -14,10 +14,19 @@ import "fmt" var tbd string var overwrite string = "dibs" +var tbdcopy = tbd +var overwritecopy = overwrite +var arraycopy = [2]string{tbd, overwrite} + var b bool var x int func main() { fmt.Println(tbd) + fmt.Println(tbdcopy) + fmt.Println(arraycopy[0]) + fmt.Println(overwrite) + fmt.Println(overwritecopy) + fmt.Println(arraycopy[1]) } diff --git a/test/linkx_run.go b/test/linkx_run.go index ca9d31612a..f25053bf28 100644 --- a/test/linkx_run.go +++ b/test/linkx_run.go @@ -36,7 +36,7 @@ func test(sep string) { os.Exit(1) } - want := "hello\ntrumped\n" + want := "hello\nhello\nhello\ntrumped\ntrumped\ntrumped\n" got := out.String() if got != want { fmt.Printf("got %q want %q\n", got, want)