[gccsdk] OS_GPBP conundrum

[Gavin Wraith]

I have some code that uses OS_GPBP 12 to iterate
over objects in a directory, returning for each one
its name and filetype. It has been working for years
in RiscLua, when compiled with Norcroft and Objasm.
Now that I am using GCC the filetype is always
returned as zero, and I cannot see why.

OS_GPBP 12 uses a buffer to return its results,
with the object's name as a zero-terminated
string at buf+24, and the filetype in the word
at buf+20. I declare a buffer with

static const int rdir_buf[RDIR_BUFLEN/sizeof(int)];

After the call to OS_GPBP 12 my code grabs the
name and filetype with

lua_pushstring(L, (char *)(_buf[6])); /* name */
lua_pushinteger(L, rdir_buf[5]);   /* file type */
return 2;  /* number of returned values */

This stuff is what makes the construction

   for name, ftype in dir (foo) do  end

work - well it used to The 'name' part comes out OK, but the
'ftype' is always zero, and I just cannot see why.

--
Gavin Wraith (ga...@wra1th.plus.com)
Home page: http://www.wra1th.plus.com/

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Re: [gccsdk] OS_GPBP conundrum

[Nick Burrett]

On 21 September 2015 at 13:31, Gavin Wraith  wrote:

> I have some code that uses OS_GPBP 12 to iterate
> over objects in a directory, returning for each one
> its name and filetype. It has been working for years
> in RiscLua, when compiled with Norcroft and Objasm.
> Now that I am using GCC the filetype is always
> returned as zero, and I cannot see why.
>
> OS_GPBP 12 uses a buffer to return its results,
> with the object's name as a zero-terminated
> string at buf+24, and the filetype in the word
> at buf+20. I declare a buffer with
>
> static const int rdir_buf[RDIR_BUFLEN/sizeof(int)];
>

^ shouldn't that be static int? Wouldn't the const imply that the buffer
never changes and could be liable to some optimisation in the way members
are accessed?


Nick
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Re: [gccsdk] OS_GPBP conundrum

[Ralph Corderoy]

Hi Gavin,

> static const int rdir_buf[RDIR_BUFLEN/sizeof(int)];
...
> lua_pushstring(L, (char *)(_buf[6])); /* name */
> lua_pushinteger(L, rdir_buf[5]);   /* file type */
> return 2;  /* number of returned values */
...
> The 'name' part comes out OK, but the 'ftype' is always zero, and I
> just cannot see why.

Sounds like rdir_buf is being re-used, but only the first 24 bytes of
it, trampling the filetype, but not the filename, before the push.  Do
you see filetype in rdir_buf[5] when you lua_pushinteger() above?  If
so, what happens between the push of the correct filetype and the pull
where it's wrong?  If not, show us the OS_GPBP 12 call?

Cheers, Ralph.

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