cmd/cgo: #define is not exportable in some situations #18720

hirochachacha · 2017-01-19T22:33:48Z

Please answer these questions before submitting your issue. Thanks!

What did you do?

I know 4 failing scenarios.

package main

/*

#define PI 3.14

#define HELLO "hello"
#define WORLD "world"
#define HELLO_WORLD HELLO " " WORLD

#define VAR VAR1
#define VAR1 var

#define PAREN (var)
#define ADDR &var
#define ADDR_STAR *&var

int var = 5;

*/
import "C"

func testFloatConst() {
	if C.PI != 3.14 {
		panic("fail")
	}
}

func testStringConstPropagation() {
	if C.HELLO_WORLD != "hello world" {
		panic("fail")
	}
}

func testVariablePropagation() {
	if C.VAR != 5 {
		panic("fail")
	}
}

func testVariableIndirection() {
	if C.PAREN != 5 {
		panic("fail")
	}
	if *C.ADDR != 5 {
		panic("fail")
	}
	if C.ADDR_STAR != 5 {
		panic("fail")
	}
}

func main() {
	testFloatConst()
	testStringConstPropagation()
	testVariablePropagation()
	testVariableIndirection()
}

What did you expect to see?

no errors.

What did you see instead?

none of them can compile.

Does this issue reproduce with the latest release (go1.7.4)?

I think so.

System details

go version devel +d935b30 Tue Jan 17 12:56:29 2017 +0900 darwin/amd64
GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/hiro/.go"
GORACE=""
GOROOT="/Users/hiro/go"
GOTOOLDIR="/Users/hiro/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/wq/dwn8hs0x7njbzty9f68y61700000gn/T/go-build288724185=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
CGO_ENABLED="1"
PKG_CONFIG="pkg-config"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
GOROOT/bin/go version: go version devel +d935b30 Tue Jan 17 12:56:29 2017 +0900 darwin/amd64
GOROOT/bin/go tool compile -V: compile version devel +d935b30 Tue Jan 17 12:56:29 2017 +0900 X:framepointer
uname -v: Darwin Kernel Version 16.3.0: Thu Nov 17 20:23:58 PST 2016; root:xnu-3789.31.2~1/RELEASE_X86_64
ProductName:	Mac OS X
ProductVersion:	10.12.2
BuildVersion:	16C67
lldb --version: lldb-360.1.70
gdb --version: GNU gdb (GDB) 7.12

The text was updated successfully, but these errors were encountered:

minux · 2017-01-19T22:55:42Z

We currently only support very simple macros that simply renames a value. The reason is that to support complicated macros like *&var or even HELLO_WORLD, cgo must implement its own C parser and translate the C expression into equivalent Go. Right now, only VAR1 and HELLO work and "#define PI 3" also works, and I think we can make "#define PI 3.14" and possibly VAR work too, but I don't think we can make the others work. They might appear simple, but supporting them still requires a full C parser. The workaround is to assign the macro into a C variable or const and then use them in Go. [Updated to correct the false statement that cgo currently supports VAR as it only supports VAR1.]

hirochachacha · 2017-01-19T23:31:58Z

Thank you for quick reply!

I think we can solve testVariablePropagation also.
for example:

x.h

#define VAR VAR1
#define VAR1 var

x.txt

#include "x.h"
"VAR" = VAR

gcc -P -E -xc -c x.txt

output:

"VAR" = var

So, we can get a finalized definition, instead of a shallow definition.
before

go/src/cmd/cgo/gcc.go

Line 267 in ea7d9e6

if isName(n.Define) {

gopherbot · 2017-01-24T21:15:24Z

CL https://golang.org/cl/35511 mentions this issue.

bradfitz · 2017-03-21T01:14:45Z

For @ianlancetaylor to decide/review.

Current code doesn't support floating point #define macros. This CL compiles floats to a object file and retrive values from it. That approach is the same work as we've already done for integers. Updates #18720 Change-Id: I88b7ab174d0f73bda975cf90c5aeb797961fe034 Reviewed-on: https://go-review.googlesource.com/35511 Reviewed-by: Ian Lance Taylor <iant@golang.org> Run-TryBot: Ian Lance Taylor <iant@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org>

Current code doesn't support floating point #define macros. This CL compiles floats to a object file and retrive values from it. That approach is the same work as we've already done for integers. Updates golang#18720 Change-Id: I88b7ab174d0f73bda975cf90c5aeb797961fe034 Reviewed-on: https://go-review.googlesource.com/35511 Reviewed-by: Ian Lance Taylor <iant@golang.org> Run-TryBot: Ian Lance Taylor <iant@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org>

gopherbot · 2017-04-21T18:18:30Z

CL https://golang.org/cl/41312 mentions this issue.

gopherbot · 2017-04-27T15:27:54Z

CL https://golang.org/cl/41910 mentions this issue.

gopherbot · 2017-05-23T14:07:06Z

CL https://golang.org/cl/43970 mentions this issue.

Current code cannot handle string #define macros if those macros are defined via other macros. This CL solve the issue. Updates #18720 Change-Id: Ibed0773d10db3d545bb246b97e81c0d19e3af3d5 Reviewed-on: https://go-review.googlesource.com/41312 Reviewed-by: Ian Lance Taylor <iant@golang.org> Run-TryBot: Ian Lance Taylor <iant@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org>

ALTree · 2017-06-03T18:39:35Z

No CL for this and we're deep in the freeze, moving to go1.10.

hirochachacha · 2017-06-03T21:51:50Z

I didn't complete that because it conflicts with https://go-review.googlesource.com/c/44290/
Now, I did.

gopherbot · 2018-01-06T00:55:16Z

Change https://golang.org/cl/86475 mentions this issue: cmd/cgo: support niladic macros for gccgo

https://golang.org/cl/43970 changed writeOutputFunc to support niladic function-like macros; apply the corresponding change to writeGccgoOutputFunc. Updates #10715 Updates #18720 Change-Id: I5decb1d37ec71507466ade2eeda4b89c8785eaef Reviewed-on: https://go-review.googlesource.com/86475 Run-TryBot: Ian Lance Taylor <iant@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Hiroshi Ioka <hirochachacha@gmail.com> Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org> Reviewed-by: Austin Clements <austin@google.com>

bradfitz added this to the Go1.9Maybe milestone Mar 21, 2017

bradfitz assigned ianlancetaylor Mar 21, 2017

ALTree modified the milestones: Go1.10, Go1.9Maybe Jun 3, 2017

gopherbot closed this as completed in 03876af Aug 30, 2017

golang locked and limited conversation to collaborators Jan 6, 2019

gopherbot added the FrozenDueToAge label Jan 6, 2019

rsc unassigned ianlancetaylor Jun 23, 2022

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cmd/cgo: #define is not exportable in some situations #18720

cmd/cgo: #define is not exportable in some situations #18720

hirochachacha commented Jan 19, 2017

minux commented Jan 19, 2017 via email •

edited

hirochachacha commented Jan 19, 2017

gopherbot commented Jan 24, 2017

bradfitz commented Mar 21, 2017

gopherbot commented Apr 21, 2017

gopherbot commented Apr 27, 2017

gopherbot commented May 23, 2017

ALTree commented Jun 3, 2017

hirochachacha commented Jun 3, 2017

gopherbot commented Jan 6, 2018

cmd/cgo: #define is not exportable in some situations #18720

cmd/cgo: #define is not exportable in some situations #18720

Comments

hirochachacha commented Jan 19, 2017

What did you do?

What did you expect to see?

What did you see instead?

Does this issue reproduce with the latest release (go1.7.4)?

System details

minux commented Jan 19, 2017 via email • edited

hirochachacha commented Jan 19, 2017

gopherbot commented Jan 24, 2017

bradfitz commented Mar 21, 2017

gopherbot commented Apr 21, 2017

gopherbot commented Apr 27, 2017

gopherbot commented May 23, 2017

ALTree commented Jun 3, 2017

hirochachacha commented Jun 3, 2017

gopherbot commented Jan 6, 2018

minux commented Jan 19, 2017 via email •

edited