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gccgo: reflect.Value.Call fails with struct with empty struct field #26335

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ianlancetaylor opened this issue Jul 11, 2018 · 2 comments
Closed

gccgo: reflect.Value.Call fails with struct with empty struct field #26335

ianlancetaylor opened this issue Jul 11, 2018 · 2 comments
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FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done.
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Gccgo

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@ianlancetaylor
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This test case crashes when compiled with gccgo. The parameter s is read from the wrong position on the stack. The problem is most likely that the empty struct field in large leads to a disagreement between the Go code and libffi.

package main

import (
	"fmt"
	"reflect"
)

type large struct {
	f1, f2, f3, f4 *byte
	empty struct{}
}

func F(str string, l large, s []string) {
	if len(s) != 1 || s[0] != "hi" {
		fmt.Printf("bad value for s: %v\n", s)
		panic("bad slice")
	}
}

func main() {
	params := []reflect.Value{
		reflect.ValueOf("str"),
		reflect.ValueOf(large{}),
		reflect.ValueOf([]string{"hi"}),
	}
	reflect.ValueOf(F).Call(params)
}
@ianlancetaylor ianlancetaylor added the NeedsFix The path to resolution is known, but the work has not been done. label Jul 11, 2018
@ianlancetaylor ianlancetaylor added this to the Gccgo milestone Jul 11, 2018
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Change https://golang.org/cl/123316 mentions this issue: test: add test case that failed with gccgo

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Change https://golang.org/cl/123335 mentions this issue: runtime: skip zero-sized fields in structs when converting to FFI

gopherbot pushed a commit that referenced this issue Jul 11, 2018
@ianlancetaylor
test: add test case that failed with gccgo
787ff17 
Updates #26335

Change-Id: Ibfb1e232a0c66fa699842c8908ae5ff0f5d2177d
Reviewed-on: https://go-review.googlesource.com/123316
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
hubot pushed a commit to gcc-mirror/gcc that referenced this issue Jul 13, 2018
runtime: skip zero-sized fields in structs when converting to FFI
e1f7ba0 
    
    The libffi library doesn't understand zero-sized objects.
    When we see a zero-sized field in a struct, just skip it when
    converting to the FFI data structures. There is no value to pass in
    any case, so not telling libffi about the field doesn't affect
    anything.
    
    The test case for this is https://golang.org/cl/123316.
    
    Fixes golang/go#26335
    
    Reviewed-on: https://go-review.googlesource.com/123335


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@262651 138bc75d-0d04-0410-961f-82ee72b054a4
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