Interface with C codes

Interface with C codes

[Anh Vo]

What Ada spec should be for the following C prototype where BOOT_PARAMS is a struct and responding Ada type is

type Boot_Parameter_Type is
   record
      Boot_Dev : Interfaces.C.Strings.Chars_Ptr;
      -- ...
   end record;
pragma Convention (C, Boot_Parameter_Type);

type Boot_Parameter_Type_Access is access Boot_Parameter_Type;
pragma Convention (C, Boot_Parameter_Type_Access);


typedef struct           /* BOOT_PARAMS */
    {
    char bootDev [20];  /* boot device code */
    * ... *
    } BOOT_PARAMS;

Note that I can not use Ada 2012 yet.


char *  bootStringToStruct (char * bootString,  BOOT_PARAMS * pBootParams);


Anh Vo

Re: Interface with C codes

[Anh Vo]

On Friday, October 17, 2014 4:22:15 PM UTC-7, Anh Vo wrote:
> What Ada spec should be for the following C prototype where BOOT_PARAMS is a struct and responding Ada type is
>  
> 
> type Boot_Parameter_Type is
> 
>    record 
>       Boot_Dev : Interfaces.C.Strings.Chars_Ptr; 
>       -- ... 
>    end record;
> 
> pragma Convention (C, Boot_Parameter_Type);
>  
> 
> type Boot_Parameter_Type_Access is access Boot_Parameter_Type;
> 
> pragma Convention (C, Boot_Parameter_Type_Access);
>  
> typedef struct           /* BOOT_PARAMS */ 
>     { 
>     char bootDev [20];  /* boot device code */ 
>     * ... * 
>     } BOOT_PARAMS;
>   
> Note that I can not use Ada 2012 yet.
>  
> char *  bootStringToStruct (char * bootString,  BOOT_PARAMS * pBootParams); 
 
> Anh Vo

Should this one work?

function Boot_String_To_Type (
           Boot_String : Interfaces.C.Strings.chars_ptr;
           Boot_Params : Boot_Parameter_Type_Access) 
                             return Interfaces.C.Strings.chars_ptr;
pragma Import (C, Boot_String_To_Type, "bootStringToStruct");

Re: Interface with C codes

[Adam Beneschan]

On Friday, October 17, 2014 4:22:15 PM UTC-7, Anh Vo wrote:
> What Ada spec should be for the following C prototype where BOOT_PARAMS is a struct and responding Ada type is
> 
> type Boot_Parameter_Type is
>    record
>       Boot_Dev : Interfaces.C.Strings.Chars_Ptr;
>       -- ...
>    end record;
> 
> pragma Convention (C, Boot_Parameter_Type);
> 
> type Boot_Parameter_Type_Access is access Boot_Parameter_Type;
> pragma Convention (C, Boot_Parameter_Type_Access);

> typedef struct           /* BOOT_PARAMS */
>     {
>     char bootDev [20];  /* boot device code */
>     * ... *
>     } BOOT_PARAMS;
> 
> Note that I can not use Ada 2012 yet.
> 
> char *  bootStringToStruct (char * bootString,  BOOT_PARAMS * pBootParams);
> 
> Anh Vo

I'm confused.  You've defined an Ada record Boot_Parameter_Type that has a pointer in it, and a C struct that does not have a pointer. 

                                -- Adam

Re: Interface with C codes

[Anh Vo]

On Friday, October 17, 2014 4:49:04 PM UTC-7, Adam Beneschan wrote:
> On Friday, October 17, 2014 4:22:15 PM UTC-7, Anh Vo wrote:
> 
> > What Ada spec should be for the following C prototype where BOOT_PARAMS is a struct and responding Ada type is
> 
> > 
> 
> > type Boot_Parameter_Type is
> 
> >    record
> 
> >       Boot_Dev : Interfaces.C.Strings.Chars_Ptr;
> 
> >       -- ...
> 
> >    end record;
> 
> > 
> 
> > pragma Convention (C, Boot_Parameter_Type);
> 
> > 
> 
> > type Boot_Parameter_Type_Access is access Boot_Parameter_Type;
> 
> > pragma Convention (C, Boot_Parameter_Type_Access);
> 
> 
> 
> > typedef struct           /* BOOT_PARAMS */
> 
> >     {
> 
> >     char bootDev [20];  /* boot device code */
> 
> >     * ... *
> 
> >     } BOOT_PARAMS;
> 
> > 
> 
> > Note that I can not use Ada 2012 yet.
> 
> > 
> 
> > char *  bootStringToStruct (char * bootString,  BOOT_PARAMS * pBootParams);
> 
> > 
> 
> > Anh Vo
> 
> I'm confused.  You've defined an Ada record Boot_Parameter_Type that has a pointer in it, and a C struct that does not have a pointer. 
> 

The second parameter of the function prototype use pointer, BOOT_PARAMS * pBootParams.

Anh Vo

Re: Interface with C codes

[Anh Vo]

On Friday, October 17, 2014 5:04:17 PM UTC-7, Anh Vo wrote:
> On Friday, October 17, 2014 4:49:04 PM UTC-7, Adam Beneschan wrote:
> 
> > On Friday, October 17, 2014 4:22:15 PM UTC-7, Anh Vo wrote:
> > 
> > > What Ada spec should be for the following C prototype where BOOT_PARAMS is a struct and responding Ada type is
> 
> > > type Boot_Parameter_Type is
> > >    record
> > >       Boot_Dev : Interfaces.C.Strings.Chars_Ptr;
> > >       -- ...
> > >    end record;
> > > pragma Convention (C, Boot_Parameter_Type);
> > 
> > > type Boot_Parameter_Type_Access is access Boot_Parameter_Type;
> > > pragma Convention (C, Boot_Parameter_Type_Access);
> > 
> > > typedef struct           /* BOOT_PARAMS */
> > >     {
> > >     char bootDev [20];  /* boot device code */
> > >     * ... *
> > >     } BOOT_PARAMS;
> > 
> > > Note that I can not use Ada 2012 yet.
> > 
> > > char *  bootStringToStruct (char * bootString,  BOOT_PARAMS * pBootParams); 
> > 
> > I'm confused.  You've defined an Ada record Boot_Parameter_Type that has a pointer in it, and a C struct that does not have a pointer. 
> 
> > 
> The second parameter of the function prototype use pointer, BOOT_PARAMS * pBootParams.
> 

How this one.

function Boot_String_To_Type (
           Boot_String : Interfaces.C.Strings.chars_ptr;
           Boot_Params : System.Address) 
                             return Interfaces.C.Strings.chars_ptr;
pragma Import (C, Boot_String_To_Type, "bootStringToStruct");

Re: Interface with C codes

[Jeffrey Carter]

On 10/17/2014 04:22 PM, Anh Vo wrote:
> What Ada spec should be for the following C prototype where BOOT_PARAMS is a struct and responding Ada type is
> 
> type Boot_Parameter_Type is
>    record
>       Boot_Dev : Interfaces.C.Strings.Chars_Ptr;

This doesn't match the C quoted below. Use

                   Interfaces.C.Char_Array (0 .. 19);

>       -- ...
>    end record;
> pragma Convention (C, Boot_Parameter_Type);
> 
> type Boot_Parameter_Type_Access is access Boot_Parameter_Type;
> pragma Convention (C, Boot_Parameter_Type_Access);

You don't need this access type.

> char *  bootStringToStruct (char * bootString,  BOOT_PARAMS * pBootParams);

I would probably use

function To_Record
(Boot_String : Intefaces.C.Char_Array; Boot_Parameter : Boot_Parameter_Type)
return Interfaces.C.Strings.Chars_Ptr;

and rely on the advice in B.3(69-70): both parameters will be passed by reference.

-- 
Jeff Carter
"Whatever it is, I'm against it."
Horse Feathers
46

Re: Interface with C codes

[Per Sandberg]

Ask the compiler
g++ -fdump-ada-spec ${header}
/Per

On 18.10.2014 01:22, Anh Vo wrote:
> What Ada spec should be for the following C prototype where BOOT_PARAMS is a struct and responding Ada type is
>
> type Boot_Parameter_Type is
>     record
>        Boot_Dev : Interfaces.C.Strings.Chars_Ptr;
>        -- ...
>     end record;
> pragma Convention (C, Boot_Parameter_Type);
>
> type Boot_Parameter_Type_Access is access Boot_Parameter_Type;
> pragma Convention (C, Boot_Parameter_Type_Access);
>
>
> typedef struct           /* BOOT_PARAMS */
>      {
>      char bootDev [20];  /* boot device code */
>      * ... *
>      } BOOT_PARAMS;
>
> Note that I can not use Ada 2012 yet.
>
>
> char *  bootStringToStruct (char * bootString,  BOOT_PARAMS * pBootParams);
>
>
> Anh Vo
>

Re: Interface with C codes

[Anh Vo]

On Friday, October 17, 2014 7:20:45 PM UTC-7, Jeffrey Carter wrote:
> On 10/17/2014 04:22 PM, Anh Vo wrote:
> 
> > What Ada spec should be for the following C prototype where BOOT_PARAMS is a struct and responding Ada type is 
> >  
> > type Boot_Parameter_Type is 
> >    record 
> >       Boot_Dev : Interfaces.C.Strings.Chars_Ptr; 
> This doesn't match the C quoted below. Use
>                    Interfaces.C.Char_Array (0 .. 19);

Thanks for that.
> 
> >       -- ...
> 
> >    end record;
> > pragma Convention (C, Boot_Parameter_Type); 
> >  
> > type Boot_Parameter_Type_Access is access Boot_Parameter_Type; 
> > pragma Convention (C, Boot_Parameter_Type_Access);
> 
> You don't need this access type.
> 
> > char *  bootStringToStruct (char * bootString,  BOOT_PARAMS * pBootParams);
> 
> I would probably use

> function To_Record 
> (Boot_String : Intefaces.C.Char_Array; Boot_Parameter : Boot_Parameter_Type) 
> return Interfaces.C.Strings.Chars_Ptr;

> and rely on the advice in B.3(69-70): both parameters will be passed by reference.

Thanks again. I have enough info to test it out. 

Anh Vo

Re: Interface with C codes

[Anh Vo]

On Friday, October 17, 2014 11:27:24 PM UTC-7, Per Sandberg wrote:
> Ask the compiler 
> g++ -fdump-ada-spec ${header}

I did just exactly that. But, I had a problem because at least one of the included header in the included chain was not available.

I will create a stand alone header containing truct and function prototype only. Then, use g++ -fdump-ada-spec to generate the binding. 

Thank you all for your suggestions.

Anh Vo

Re: Interface with C codes

[Simon Wright]

Anh Vo <anhvofrcaus@gmail.com> writes:

> On Friday, October 17, 2014 11:27:24 PM UTC-7, Per Sandberg wrote:
>> Ask the compiler 
>> g++ -fdump-ada-spec ${header}
>
> I did just exactly that. But, I had a problem because at least one of
> the included header in the included chain was not available.

Sometimes -fdump-ada-spec-slim will solve that for you.

Re: Interface with C codes

[Stephen Leake]

Anh Vo <anhvofrcaus@gmail.com> writes:

> On Friday, October 17, 2014 4:22:15 PM UTC-7, Anh Vo wrote:
>>  
>> char *  bootStringToStruct (char * bootString,  BOOT_PARAMS * pBootParams); 
>  
>> Anh Vo
>
> Should this one work?
>
> function Boot_String_To_Type (
>            Boot_String : Interfaces.C.Strings.chars_ptr;
>            Boot_Params : Boot_Parameter_Type_Access) 
>                              return Interfaces.C.Strings.chars_ptr;
> pragma Import (C, Boot_String_To_Type, "bootStringToStruct");

Looks good. but give -fdump-ada-spec a try.

-- 
-- Stephe

Re: Interface with C codes

[Anh Vo]

On Saturday, October 18, 2014 11:33:32 AM UTC-7, Stephen Leake wrote:
> Anh Vo <anhvofrcaus@gmail.com> writes:
> > On Friday, October 17, 2014 4:22:15 PM UTC-7, Anh Vo wrote:
> >>  
> >> char *  bootStringToStruct (char * bootString,  BOOT_PARAMS * pBootParams); 
> >  
> > Should this one work?
> >
> > function Boot_String_To_Type (
> >            Boot_String : Interfaces.C.Strings.chars_ptr;
> >            Boot_Params : Boot_Parameter_Type_Access) 
> >                              return Interfaces.C.Strings.chars_ptr; 
> > pragma Import (C, Boot_String_To_Type, "bootStringToStruct");
> 
> Looks good. but give -fdump-ada-spec a try.

Yes, I tried and the result is below.

function bootStringToStruct (bootString : Interfaces.C.Strings.chars_ptr;
                                pBootParams : access BOOT_PARAMS)
                                   return Interfaces.C.Strings.chars_ptr;
pragma Import (CPP, bootStringToStruct,  "_Z18bootStringToStructPcP11BOOT_PARAMS");

Why was "_Z18bootStringToStructPcP11BOOT_PARAMS" generated for third parameter of pragma Import? I thought it should be "bootStringToStruct".

A. Vo
 

Re: Interface with C codes

[Simon Clubley]

On 2014-10-19, Anh Vo <anhvofrcaus@gmail.com> wrote:
> On Saturday, October 18, 2014 11:33:32 AM UTC-7, Stephen Leake wrote:
>> Anh Vo <anhvofrcaus@gmail.com> writes:
>> > On Friday, October 17, 2014 4:22:15 PM UTC-7, Anh Vo wrote:
>> >>  
>> >> char *  bootStringToStruct (char * bootString,  BOOT_PARAMS * pBootParams); 
>> >  
>> > Should this one work?
>> >
>> > function Boot_String_To_Type (
>> >            Boot_String : Interfaces.C.Strings.chars_ptr;
>> >            Boot_Params : Boot_Parameter_Type_Access) 
>> >                              return Interfaces.C.Strings.chars_ptr; 
>> > pragma Import (C, Boot_String_To_Type, "bootStringToStruct");
>> 
>> Looks good. but give -fdump-ada-spec a try.
>
> Yes, I tried and the result is below.
>
> function bootStringToStruct (bootString : Interfaces.C.Strings.chars_ptr;
>                                 pBootParams : access BOOT_PARAMS)
>                                    return Interfaces.C.Strings.chars_ptr;
> pragma Import (CPP, bootStringToStruct,  "_Z18bootStringToStructPcP11BOOT_PARAMS");
>
> Why was "_Z18bootStringToStructPcP11BOOT_PARAMS" generated for third parameter of pragma Import? I thought it should be "bootStringToStruct".
>

It's known as a mangled symbol and is required with C++ (notice your
latter example is using "CPP" and not "C" on the pragma Import).

The "Name mangling in C++" section of the following might be useful:

http://en.wikipedia.org/wiki/Name_mangling

Simon.

-- 
Simon Clubley, clubley@remove_me.eisner.decus.org-Earth.UFP
Microsoft: Bringing you 1980s technology to a 21st century world

Re: Interface with C codes

[Brian Drummond]

On Sat, 18 Oct 2014 21:33:03 -0700, Anh Vo wrote:

> On Saturday, October 18, 2014 11:33:32 AM UTC-7, Stephen Leake wrote:
>> Anh Vo <anhvofrcaus@gmail.com> writes:
>> > On Friday, October 17, 2014 4:22:15 PM UTC-7, Anh Vo wrote:
>> >>  
>> >> char *  bootStringToStruct (char * bootString,  BOOT_PARAMS *
>> >> pBootParams);
>> >  
>> > Should this one work?
>> >
>> > function Boot_String_To_Type (
>> >            Boot_String : Interfaces.C.Strings.chars_ptr;
>> >            Boot_Params : Boot_Parameter_Type_Access)
>> >                              return Interfaces.C.Strings.chars_ptr;
>> > pragma Import (C, Boot_String_To_Type, "bootStringToStruct");
>> 
>> Looks good. but give -fdump-ada-spec a try.
> 
> Yes, I tried and the result is below.
(C++ snipped)

Use gcc -fdump-ada-spec instead of g++ -fdump-ada-spec

- Brian

Re: Interface with C codes

[Simon Wright]

Brian Drummond <brian3@shapes.demon.co.uk> writes:

> Use gcc -fdump-ada-spec instead of g++ -fdump-ada-spec

g++ does a better job, they say, but you need to use extern "C":

extern "C" {
   // C declarations go here
}

Re: Interface with C codes

[Anh Vo]

On Sunday, October 19, 2014 6:58:18 AM UTC-7, Simon Wright wrote:
> Brian Drummond <brian3@shapes.demon.co.uk> writes:
> > Use gcc -fdump-ada-spec instead of g++ -fdump-ada-spec
> 
> g++ does a better job, they say, but you need to use extern "C":
> extern "C" { 
>    // C declarations go here 
> }

Both ways worked fine. Thank you all very much for the info.

A. Vo

Re: Interface with C codes

[Adam Beneschan]

On Friday, October 17, 2014 5:04:17 PM UTC-7, Anh Vo wrote:

> > I'm confused.  You've defined an Ada record Boot_Parameter_Type that has a pointer in it, and a C struct that does not have a pointer. 

> The second parameter of the function prototype use pointer, BOOT_PARAMS * pBootParams.

My point was that if you have a record layout in Ada that has a pointer in it, and your record (struct) type definition in C doesn't have a pointer, there will be major problems.  The Ada program will pass a record that has (typically) 4 or 8 bytes of pointer data, but the C program will be expecting those bytes to be character data (and since it actually expects there to be 20 characters, it will be looking for character data past the end of the Ada record, possibly looking into other Ada variables or worse).  Jeff already addressed this by suggesting you change Boot_Dev's type to Char_Array.  

                                -- Adam

Re: Interface with C codes

[Anh Vo]

On Monday, October 20, 2014 9:14:25 AM UTC-7, Adam Beneschan wrote:
> On Friday, October 17, 2014 5:04:17 PM UTC-7, Anh Vo wrote:
> 
>>> I'm confused.  You've defined an Ada record Boot_Parameter_Type that has a pointer in it, and a C struct that does not have a pointer. 
> 
>> The second parameter of the function prototype use pointer, BOOT_PARAMS * pBootParams.
> 
> My point was that if you have a record layout in Ada that has a pointer in it, and your record (struct) type definition in C doesn't have a pointer, there will be major problems.  The Ada program will pass a record that has (typically) 4 or 8 bytes of pointer data, but the C program will be expecting those bytes to be character data (and since it actually expects there to be 20 characters, it will be looking for character data past the end of the Ada record, possibly looking into other Ada variables or worse).  Jeff already addressed this by suggesting you change Boot_Dev's type to Char_Array.  
> 

You are right. I ended up to use the g++ -fdump-ada-spec suggested by Per Sandberg and others. Yes, the Boot_Dev's is defined Char_Array type. The good news is that it worked good. Again, thank you all for your help.

Anh Vo