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cmd/cgo: exported function name shadowing issue #44974

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pmuetschard opened this issue Mar 12, 2021 · 2 comments
Open

cmd/cgo: exported function name shadowing issue #44974

pmuetschard opened this issue Mar 12, 2021 · 2 comments

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@pmuetschard
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@pmuetschard pmuetschard commented Mar 12, 2021

What version of Go are you using (go version)?

$ go version
go version go1.16.2 linux/amd64

Does this issue reproduce with the latest release?

Yes, this was introduced somewhere between 1.14 and 1.16.

What operating system and processor architecture are you using (go env)?

go env Output
$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/xxx/.cache/go-build"
GOENV="/home/xxx/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/xxx/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/xxx/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/home/xxx/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/xxx/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.16.2"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/dev/null"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build2817633273=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Attempting to compile the following snippet fails in 1.16:

package baz

// typedef struct { int x; } foo;
import "C"

//export bar
func bar(foo *C.foo) {
}
$ /xxx/go1.14/bin/go build foo.go 
$ /xxx/go1.16.2/bin/go build foo.go 
# command-line-arguments
_cgo_export.c: In function ‘bar’:
_cgo_export.c:28:3: error: expected specifier-qualifier-list before ‘foo’
   28 |   foo* p0;
      |   ^~~
_cgo_export.c:32:8: error: ‘_cgo_argtype’ {aka ‘struct <anonymous>’} has no member named ‘p0’
   32 |  _cgo_a.p0 = foo;
      |        ^

The generated C code fails to compile, because of the overloaded foo name (variable shadowing the type):

void bar(foo* foo) {
        typedef struct {
                foo* p0; // <---- fails here
        } __attribute__((__packed__, __gcc_struct__)) _cgo_argtype;
}

With 1.14, the generated code doesn't use the name from the go code, and so doesn't have this issue:

void bar(foo* p0) {
	struct {
		foo* p0;
	} __attribute__((__packed__, __gcc_struct__)) a;

What did you expect to see?

No build failure.

What did you see instead?

Build failure.

@dmitshur dmitshur changed the title cgo exported function name shadowing issue cmd/cgo: exported function name shadowing issue Mar 12, 2021
@dmitshur
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@dmitshur dmitshur commented Mar 12, 2021

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@dmitshur dmitshur added this to the Backlog milestone Mar 12, 2021
@ianlancetaylor
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@ianlancetaylor ianlancetaylor commented Mar 15, 2021

This was broken by https://golang.org/cl/222619. I don't see an obvious path forward other than reverting that change.

CC @nathan-fiscaletti

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