diff options
author | Matthew Dempsky <mdempsky@google.com> | 2019-10-03 10:49:28 -0700 |
---|---|---|
committer | Matthew Dempsky <mdempsky@google.com> | 2019-10-03 18:08:32 +0000 |
commit | c33d45a898ab1d966faba33d18acdffefb0fae0d (patch) | |
tree | 425b1208dde73aa82fb5e1adf8f9f382a50e46ee | |
parent | 6b85fa80519615ae5fd58154277b47d77e5cf08b (diff) | |
download | go-git-c33d45a898ab1d966faba33d18acdffefb0fae0d.tar.gz |
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 <mdempsky@google.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
-rw-r--r-- | src/cmd/compile/internal/gc/sinit.go | 3 | ||||
-rw-r--r-- | test/linkx.go | 9 | ||||
-rw-r--r-- | test/linkx_run.go | 2 |
3 files changed, 13 insertions, 1 deletions
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) |