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cmd/cgo: request for better error messages #8442

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gopherbot opened this issue Jul 29, 2014 · 11 comments

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@gopherbot
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commented Jul 29, 2014

by rogerpack2005:

What does 'go version' print?

go version go1.3 windows/386

What steps reproduce the problem?
If possible, include a link to a program on play.golang.org.

While trying to debug compiler failures with "cgo" files, for instance this:

http://play.golang.org/p/T8qEZaV_Vu

> go.exe run yo.go
# command-line-arguments
37: error: 'EnumProcesses' undeclared (first use in this function)

Is the error message.  Which leaves you scratching your head, since it *is* declared in
one of the include files.
The real problem in this case, is that basically, the includes are in the wrong order,
in GCC I get "warnings" like this:

c:\devkit451\mingw\bin\../lib/gcc/mingw32/4.5.1/../../../../include/psapi.h:30:2: error:
expected specifier-qualifier-list before ‘LPVOID’

To warn me that something is amiss--go doesn't seem to give me any warnings, just a
misleading error message.  Using it with the "-work" parameter also doesn't
seem to spit out any useful to look at files.

It would be really good if it noted to you that the C files it compiles with your
snippet don't work *at all*.
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commented Jul 30, 2014

Comment 1 by camilo.aguilar:

I'm also puzzled by an error happening only on Linux: 
camilo@ubuntu:~/shares/Development/go/src/github.com/c4milo/govix$ make
go build
# github.com/c4milo/govix
38: error: 'free' undeclared (first use in this function)
make: *** [build] Error 2
In OSX it compiles just fine.
Error messages are very useless in CGO.
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commented Jul 31, 2014

Comment 2:

Labels changed: added repo-main, release-none, suggested.

@mdempsky

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commented Aug 6, 2014

Comment 3:

Could either of you try to provide a more minimized test case for this issue? 
Preferably a self-contained .go file that doesn't depend on any system headers.
I spent a little bit trying to repro this issue, and haven't had any success as the
error messages cgo outputs seem adequately informative to me.  E.g., based on the first
"expected specifier-qualifier-list before 'LPVOID'" error I tried reproducing that based
on the code from
http://stackoverflow.com/questions/3888569/expected-specifier-qualifier-list-before:
$ cat issue8442.go
package main
/*
typedef struct {
  foo *f;
} foo;
int bar(void);
*/
import "C"
var _ = C.bar
func main() {
}
$ go run issue8442.go
# command-line-arguments
./issue8442.go:5:3: error: unknown type name 'foo'
   foo *f;
   ^
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commented Aug 7, 2014

Comment 4:

> ... Could either of you try to provide a more minimized test case for this issue? 
Is http://play.golang.org/p/T8qEZaV_Vu not small enough? Please, explain.
> ... Preferably a self-contained .go file that doesn't depend on any system headers.
As I understand this issue, it is C "include" statement order that causes the error and
misunderstanding here. So we won't be able to have sample code without "system headers".
> ... the error messages cgo outputs seem adequately informative to me. ...
Are you saying the quoted above message:
37: error: 'EnumProcesses' undeclared (first use in this function)
is informative? But, like rogerpack2005 says, EnumProcesses "... *is* declared in one of
the include files". cgo is wrong here.
Alex
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commented Aug 7, 2014

Comment 5:

I would guess that mdempsky can't recreate the problem because he isn't running Windows
(and neither am I).  I don't understand how the header files could be the problem, but
if they are in fact the problem, it should be possible to put together a standalone test
case that provides the header files being used.
Note that the error here is coming from gcc, not cgo.  It might help to show us the "go
build -x" output.
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commented Aug 7, 2014

Comment 6 by rogerpack2005:

Maybe this one? http://play.golang.org/p/qVc3hJYve-
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commented Aug 7, 2014

Comment 7:

Thanks for the example.  It uses various undefined names, and that seems to be the
problem.  Here is a simpler case:
package p
 
//int F(UNDEF*);
import "C"
 
func F() {
    C.F(nil);
}
> go build foo.go
# command-line-arguments
37: error: 'F' undeclared (first use in this function)
Running cgo with the -debug-gcc option gives me this:
$ gcc -E -dM -xc -m64 -I /tmp/go-build581285178/command-line-arguments/_obj/ -
<<EOF
#line 3 "/home/iant/foo.go"
int F(UNDEF*);
#include <stddef.h> /* for ptrdiff_t and size_t below */
/* Define intgo when compiling with GCC.  */
typedef ptrdiff_t intgo;
typedef struct { char *p; intgo n; } _GoString_;
typedef struct { char *p; intgo n; intgo c; } _GoBytes_;
_GoString_ GoString(char *p);
_GoString_ GoStringN(char *p, int l);
_GoBytes_ GoBytes(void *p, int n);
char *CString(_GoString_);
void *_CMalloc(size_t);
EOF
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#define _T_WCHAR_ 
#define __INTMAX_C(c) c ## L
#define __CHAR_BIT__ 8
#define __UINT8_MAX__ 255
#define __WINT_MAX__ 4294967295U
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#define __SIZE_MAX__ 18446744073709551615UL
#define __WCHAR_MAX__ 2147483647
#define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_1 1
#define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_2 1
#define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4 1
#define __DBL_DENORM_MIN__ ((double)4.94065645841246544177e-324L)
#define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_8 1
#define __FLT_EVAL_METHOD__ 0
#define __unix__ 1
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#define __UINT_FAST64_MAX__ 18446744073709551615UL
#define __SIG_ATOMIC_TYPE__ int
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#define __STDDEF_H__ 
#define __GNUC_PATCHLEVEL__ 3
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#define __size_t 
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#define _WCHAR_T_DEFINED 
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#define __UINT16_C(c) c
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#define _T_PTRDIFF 
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#define offsetof(TYPE,MEMBER) __builtin_offsetof (TYPE, MEMBER)
#define __FLT_HAS_DENORM__ 1
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#define __DBL_MAX__ ((double)1.79769313486231570815e+308L)
#define __INT_FAST32_MAX__ 9223372036854775807L
#define __DBL_HAS_INFINITY__ 1
#define __DEC32_MIN_EXP__ (-94)
#define __INT_FAST16_TYPE__ long int
#define _SIZE_T_DEFINED 
#define _WCHAR_T_DEFINED_ 
#define __LDBL_HAS_DENORM__ 1
#define __DEC128_MAX__ 9.999999999999999999999999999999999E6144DL
#define __INT_LEAST32_MAX__ 2147483647
#define __DEC32_MIN__ 1E-95DF
#define __DBL_MAX_EXP__ 1024
#define __DEC128_EPSILON__ 1E-33DL
#define __SSE2_MATH__ 1
#define __PTRDIFF_MAX__ 9223372036854775807L
#define __amd64 1
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#define _PTRDIFF_T 
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#define __PTRDIFF_T 
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#define __UINT64_C(c) c ## UL
#define _PTRDIFF_T_ 
#define __INT_WCHAR_T_H 
#define _T_PTRDIFF_ 
#define _SYS_SIZE_T_H 
#define __FLOAT_WORD_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __SIZE_T__ 
#define __INT32_C(c) c
#define __DEC64_EPSILON__ 1E-15DD
#define __ORDER_PDP_ENDIAN__ 3412
#define __DEC128_MIN_EXP__ (-6142)
#define __INT_FAST32_TYPE__ long int
#define __UINT_LEAST16_TYPE__ short unsigned int
#define unix 1
#define __INT16_MAX__ 32767
#define _BSD_SIZE_T_ 
#define __SIZE_TYPE__ long unsigned int
#define __UINT64_MAX__ 18446744073709551615UL
#define _SIZE_T_DECLARED 
#define __INT8_TYPE__ signed char
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#define __FLT_RADIX__ 2
#define __INT_LEAST16_TYPE__ short int
#define __LDBL_EPSILON__ 1.08420217248550443401e-19L
#define __UINTMAX_C(c) c ## UL
#define __SSE_MATH__ 1
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#define __SIZEOF_PTRDIFF_T__ 8
#define __x86_64__ 1
#define _SIZE_T_ 
#define __DEC32_SUBNORMAL_MIN__ 0.000001E-95DF
#define _WCHAR_T_H 
#define __INT_FAST16_MAX__ 9223372036854775807L
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#define __DEC32_MAX_EXP__ 97
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#define _WCHAR_T_DECLARED 
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#define __INT64_TYPE__ long int
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#define __DBL_EPSILON__ ((double)2.22044604925031308085e-16L)
#define _SIZET_ 
#define _LP64 1
#define __UINT8_C(c) c
#define __INT_LEAST32_TYPE__ int
#define __wchar_t__ 
#define __SIZEOF_WCHAR_T__ 4
#define __UINT64_TYPE__ long unsigned int
#define _STDDEF_H_ 
#define __INT_FAST8_TYPE__ signed char
#define __DBL_DECIMAL_DIG__ 17
#define __DEC_EVAL_METHOD__ 2
#define _SIZE_T 
#define _GCC_SIZE_T 
#define __UINT32_C(c) c ## U
#define __INTMAX_MAX__ 9223372036854775807L
#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __size_t__ 
#define __FLT_DENORM_MIN__ 1.40129846432481707092e-45F
#define __INT8_MAX__ 127
#define __UINT_FAST32_TYPE__ long unsigned int
#define __CHAR32_TYPE__ unsigned int
#define __FLT_MAX__ 3.40282346638528859812e+38F
#define __INT32_TYPE__ int
#define __SIZEOF_DOUBLE__ 8
#define __FLT_MIN_10_EXP__ (-37)
#define __INTMAX_TYPE__ long int
#define __DEC128_MAX_EXP__ 6145
#define _T_SIZE 
#define __GNUC_MINOR__ 6
#define __UINTMAX_MAX__ 18446744073709551615UL
#define __DEC32_MANT_DIG__ 7
#define __DBL_MAX_10_EXP__ 308
#define __LDBL_DENORM_MIN__ 3.64519953188247460253e-4951L
#define __INT16_C(c) c
#define __STDC__ 1
#define __PTRDIFF_TYPE__ long int
#define __UINT32_TYPE__ unsigned int
#define __UINTPTR_TYPE__ long unsigned int
#define __DEC64_SUBNORMAL_MIN__ 0.000000000000001E-383DD
#define __DEC128_MANT_DIG__ 34
#define __LDBL_MIN_10_EXP__ (-4931)
#define __SIZEOF_LONG_LONG__ 8
#define _GCC_PTRDIFF_T 
#define __LDBL_DIG__ 18
#define __FLT_DECIMAL_DIG__ 9
#define __UINT_FAST16_MAX__ 18446744073709551615UL
#define __GNUC_GNU_INLINE__ 1
#define ___int_ptrdiff_t_h 
#define __UINT_FAST8_TYPE__ unsigned char
#define __WCHAR_T 
$ gcc -w -Wno-error -o/tmp/go-build581285178/command-line-arguments/_obj//_cgo_.o
-gdwarf-2 -c -xc -I /tmp/go-build581285178/command-line-arguments/_obj/ -m64 -
<<EOF
#line 3 "/home/iant/foo.go"
int F(UNDEF*);
#include <stddef.h> /* for ptrdiff_t and size_t below */
/* Define intgo when compiling with GCC.  */
typedef ptrdiff_t intgo;
typedef struct { char *p; intgo n; } _GoString_;
typedef struct { char *p; intgo n; intgo c; } _GoBytes_;
_GoString_ GoString(char *p);
_GoString_ GoStringN(char *p, int l);
_GoBytes_ GoBytes(void *p, int n);
char *CString(_GoString_);
void *_CMalloc(size_t);
#line 1 "not-declared"
void __cgo_f_1_1(void) { __typeof__(F) *__cgo_undefined__; }
#line 1 "not-type"
void __cgo_f_1_2(void) { F *__cgo_undefined__; }
#line 1 "not-const"
void __cgo_f_1_3(void) { enum { __cgo__undefined__ = (F)*1 }; }
#line 1 "completed"
int __cgo__1 = __cgo__2;
EOF
/home/iant/foo.go:3:7: error: unknown type name 'UNDEF'
not-declared: In function '__cgo_f_1_1':
not-declared:1:37: error: 'F' undeclared (first use in this function)
not-declared:1:37: note: each undeclared identifier is reported only once for each
function it appears in
not-type: In function '__cgo_f_1_2':
not-type:1:26: error: unknown type name 'F'
not-const: In function '__cgo_f_1_3':
not-const:1:55: error: 'F' undeclared (first use in this function)
completed: At top level:
completed:1:16: error: '__cgo__2' undeclared here (not in a function)
37: error: 'F' undeclared (first use in this function)
The error message is correct in a sense--F is not declared because the declaration is
erroneous--but in context it is very unhelpful.
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commented Aug 8, 2014

Comment 8:

Ian,
Here is what I see here. If I run this http://play.golang.org/p/T8qEZaV_Vu as is, I get:
C:\go\path\mine\src\issue8442>go run a.go
# command-line-arguments
37: error: 'EnumProcesses' undeclared (first use in this function)
C:\go\path\mine\src\issue8442>
But if I change the program a little:
C:\go\path\mine\src\issue8442>hg diff
diff -r 81919437b8db a.go
--- a/a.go      Fri Aug 08 10:24:16 2014 +1000
+++ b/a.go      Fri Aug 08 10:24:48 2014 +1000
@@ -1,7 +1,7 @@
 package main
+// #include <windows.h>
 // #include <psapi.h>
-// #include <windows.h>
 // #cgo LDFLAGS: -lpsapi
 // #cgo CFLAGS: -DPSAPI_VERSION=1
 import "C"
C:\go\path\mine\src\issue8442>go run a.go
# command-line-arguments
.\a.go:22: cannot use (*C.uint)(unsafe.Pointer(&aProcesses[0])) (type *C.uint) as type
*C.DWORD in argument to _Cfunc_EnumProcesses
.\a.go:23: undefined: sizeof
.\a.go:23: type DWORD is not an expression
.\a.go:24: cannot use (*C.uint)(unsafe.Pointer(&cbNeeded)) (type *C.uint) as type
*C.DWORD in argument to _Cfunc_EnumProcesses
.\a.go:25: non-bool ok (type C.BOOL) used as if condition
C:\go\path\mine\src\issue8442>
The later error messages are good, because the call does not much function parameters.
But original message is misleading - it is not helpful.
I hope it helps.
Alex
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commented Aug 14, 2014

Comment 9:

CL https://golang.org/cl/129160043 mentions this issue.
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commented Aug 14, 2014

Comment 10:

This issue was closed by revision ba30c08.

Status changed to Fixed.

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commented Aug 14, 2014

Comment 11 by rogerpack2005:

Looks good thanks!

@golang golang locked and limited conversation to collaborators Jun 25, 2016

wheatman added a commit to wheatman/go-akaros that referenced this issue Jun 25, 2018
cmd/cgo: check for compiler errors in the C preamble
E.g., here's the new "go build" output:

$ go build misc/cgo/errors/issue8442.go
# command-line-arguments
could not determine kind of name for C.issue8442foo

gcc errors for preamble:
misc/cgo/errors/issue8442.go:11:19: error: unknown type name 'UNDEF'

Fixes golang#8442.

LGTM=iant
R=iant, alex.brainman
CC=golang-codereviews
https://golang.org/cl/129160043
wheatman added a commit to wheatman/go-akaros that referenced this issue Jul 9, 2018
cmd/cgo: check for compiler errors in the C preamble
E.g., here's the new "go build" output:

$ go build misc/cgo/errors/issue8442.go
# command-line-arguments
could not determine kind of name for C.issue8442foo

gcc errors for preamble:
misc/cgo/errors/issue8442.go:11:19: error: unknown type name 'UNDEF'

Fixes golang#8442.

LGTM=iant
R=iant, alex.brainman
CC=golang-codereviews
https://golang.org/cl/129160043

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