gccgo: incorrect call stack from runtime.CallersFrames #29619
Description
Stack traces are not quite right for gccgo with optimizations on (mid-stack inlining, particularly).
package main import ( "fmt" "runtime" ) func main() { f() } func f() { g() } //go:noinline func g() { for i := 0; i < 4; i++ { var pcs [1]uintptr runtime.Callers(i+1, pcs[:]) f, _ := runtime.CallersFrames(pcs[:]).Next() fmt.Printf("%x %s %s:%d\n", f.PC, f.Function, f.File, f.Line) } } Running under gc, I get:
48683c main.g /usr/local/google/home/khr/gowork/tmp5.go:19 48678f main.f /usr/local/google/home/khr/gowork/tmp5.go:12 48675f main.main /usr/local/google/home/khr/gowork/tmp5.go:9 428846 runtime.main /usr/local/google/home/khr/go1.11/src/runtime/proc.go:201 Running under gccgo -O3, I get:
56261c5ebc19 main.g /usr/local/google/home/khr/gowork/tmp5.go:19 56261c5ebeb3 main.f /usr/local/google/home/khr/gowork/tmp5.go:12 56261c5ebeb3 main.f /usr/local/google/home/khr/gowork/tmp5.go:12 7f9974ede51c runtime_main ../../../src/libgo/runtime/proc.c:606 Note the third line - that should be main.main, not a second copy of main.f.
gccgo works without -O3.
Mid-stack inlining is happening with -O3, main.main calls main.g directly. main.f isn't even in the binary.
It doesn't help to provide runtime.Callers a larger buffer.
Note that this code does work, calling runtime.Callers just once and using the runtime.CallersFrames iterator:
package main import ( "fmt" "runtime" ) func main() { f() } func f() { g() } //go:noinline func g() { var pcs [10]uintptr n := runtime.Callers(1, pcs[:]) iter := runtime.CallersFrames(pcs[:n]) for { f, more := iter.Next() fmt.Printf("%x %s %s:%d\n", f.PC, f.Function, f.File, f.Line) if !more { break } } } 55bb3972acd4 main.g /usr/local/google/home/khr/gowork/tmp6.go:18 55bb3972afc3 main.f /usr/local/google/home/khr/gowork/tmp6.go:12 55bb3972afc3 main.main /usr/local/google/home/khr/gowork/tmp6.go:9 7fa2706d451c runtime_main ../../../src/libgo/runtime/proc.c:606