mirror of https://github.com/golang/go.git
878a86a129
Fixes #10353 See test/escape2.go:issue10353. Previously new(int) did not escape to heap, and so heap-allcated closure was referencing a stack var. This breaks the invariant that heap must not contain pointers to stack. Look at the following program: package main func main() { foo(new(int)) bar(new(int)) } func foo(x *int) func() { return func() { println(*x) } } // Models what foo effectively does. func bar(x *int) *C { return &C{x} } type C struct { x *int } Without this patch escape analysis works as follows: $ go build -gcflags="-m -m -m -l" esc.go escflood:1: dst ~r1 scope:foo[0] escwalk: level:0 depth:0 func literal( l(9) f(1) esc(no) ld(1)) scope:foo[1] /tmp/live2.go:9: func literal escapes to heap escwalk: level:0 depth:1 x( l(8) class(PPARAM) f(1) esc(no) ld(1)) scope:foo[1] /tmp/live2.go:8: leaking param: x to result ~r1 escflood:2: dst ~r1 scope:bar[0] escwalk: level:0 depth:0 &C literal( l(15) esc(no) ld(1)) scope:bar[1] /tmp/live2.go:15: &C literal escapes to heap escwalk: level:-1 depth:1 &C literal( l(15)) scope:bar[0] escwalk: level:-1 depth:2 x( l(14) class(PPARAM) f(1) esc(no) ld(1)) scope:bar[1] /tmp/live2.go:14: leaking param: x /tmp/live2.go:5: new(int) escapes to heap /tmp/live2.go:4: main new(int) does not escape new(int) does not escape while being captured by the closure. With this patch escape analysis of foo and bar works similarly: $ go build -gcflags="-m -m -m -l" esc.go escflood:1: dst ~r1 scope:foo[0] escwalk: level:0 depth:0 &(func literal)( l(9)) scope:foo[0] escwalk: level:-1 depth:1 func literal( l(9) f(1) esc(no) ld(1)) scope:foo[1] /tmp/live2.go:9: func literal escapes to heap escwalk: level:-1 depth:2 x( l(8) class(PPARAM) f(1) esc(no) ld(1)) scope:foo[1] /tmp/live2.go:8: leaking param: x escflood:2: dst ~r1 scope:bar[0] escwalk: level:0 depth:0 &C literal( l(15) esc(no) ld(1)) scope:bar[1] /tmp/live2.go:15: &C literal escapes to heap escwalk: level:-1 depth:1 &C literal( l(15)) scope:bar[0] escwalk: level:-1 depth:2 x( l(14) class(PPARAM) f(1) esc(no) ld(1)) scope:bar[1] /tmp/live2.go:14: leaking param: x /tmp/live2.go:4: new(int) escapes to heap /tmp/live2.go:5: new(int) escapes to heap Change-Id: Ifd14b7ae3fc11820e3b5eb31eb07f35a22ed0932 Reviewed-on: https://go-review.googlesource.com/8408 Reviewed-by: Russ Cox <rsc@golang.org> Run-TryBot: Dmitry Vyukov <dvyukov@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> |
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