Thanks that was a valuable information. It might be the debugging flag that
caused the issue. I debugged the cgo file and found that in char* mached
with dwarf.UcharType instead of dwarf.chatType
On Monday, July 20, 2020 at 3:45:00 PM UTC-4, Ian Lance Taylor wrote:
>
> On Mon, Jul 20, 2020 at 12:28 PM Mahdi Hosseini <m.ho...@gmail.com
> <javascript:>> wrote:
> >
> > Hi,
> > I try to recompile Go for a new platform which is a s390x platform using
> Clang instead of GCC. I can not work for C string in CGO. Apparently char
> in unsigned by default on my platform and building even the simple CGO
> program always fails with this error:
> >
> > /home/user/tmp/go-build468743286/b001/_cgo_gotypes.go:175:25: undefined:
> _Ctype_char
> >
> > the code is:
> >
> > package main
> >
> > //#include <stdio.h>
> > //char* callC() {
> > // return "Calling C code!";
> > //}
> > import "C"
> >
> > import "fmt"
> >
> > func main() {
> > fmt.Println("Convert C String to Go String")
> > str := C.GoString(C.callC())
> > fmt.Println(str)
> > }
> >
> > to overcome this I modified the gcc.go file in src/cmd/cgo and added
> this:
> >
> > if s == "uchar" {
> > s = "char"
> > }
> > name := c.Ident("_Ctype_" + s)
> > I don't now how CGO always convert my char* to *_Ctype_uchar instead of
> *_Ctype_char.
> > Anyone have a clue on this?
>
> cgo is just using the debug information generated by the C compiler.
> It expects to see debug info for the type "char". For example, if I
> compile this C file
>
> #include <stdio.h>
> char* callC() {
> return "Calling C code!";
> }
>
> with clang on my system and run "readelf --debug" on the resulting
> object file, I see
>
> <1><48>: Abbrev Number: 4 (DW_TAG_base_type)
> <49> DW_AT_name : (indirect string, offset: 0x4c): char
> <4d> DW_AT_encoding : 6 (signed char)
> <4e> DW_AT_byte_size : 1
>
> cgo will use this to define the type "C.char".
>
> This is independent of whether char is signed or unsigned. Given that
> your code uses "char", it surprises me that there is no named entry
> for it in the debug info.
>
> Ian
>
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