On Mon, Jul 20, 2020 at 1:40 PM Mahdi Hosseini <m.hosein...@gmail.com> wrote:
>
> 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
I think that that in itself shouldn't matter, the question is what is
the DW_AT_name attribute of the unsigned character type.
Ian
> 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> 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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