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| Guest |
 Posted: Fri Oct 29, 2010 12:50 pm |
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Guest
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Here's another problem I found when compiling beam/io.c for IRIX.
Since The OpenGroup defines the struct iovec::iov_base field to be a
void*, it is illegal to perform pointer arithmetic on it. I'm really
surprised this didn't show up in GCC or any other compiler.
Specifically, I get these errors.
cc-3316 c99: ERROR File = beam/io.c, Line = 3343
The expression must be a pointer to a complete object type.
iov->iov_base += skip;
^
cc-3316 c99: ERROR File = beam/io.c, Line = 3795
The expression must be a pointer to a complete object type.
iov->iov_base += skip;
^
cc-3316 c99: ERROR File = beam/io.c, Line = 3858
The expression must be a pointer to a complete object type.
iov->iov_base += skip;
^
cc-3316 c99: ERROR File = beam/io.c, Line = 3918
The expression must be a pointer to a complete object type.
q->v_head->iov_base += size;
-----
The implied goal here is to increment an address by a certain number
of bytes, so casting to a char* as follows will allow the compile to
succeed:
iov->iov_base = (char*)iov->iov_base + skip;
[I had sent a message a long time ago <sys/uio.h> not being
functional, but I was mistaken. Fortunately, it looks like nobody
implemented what I said, so there isn't anything to revert.]
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| Guest |
| Posted: Fri Oct 29, 2010 1:22 pm |
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Guest
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On Fri, Oct 29, 2010 at 2:50 PM, Patrick Baggett
<baggett.patrick@gmail.com> wrote:
> Here's another problem I found when compiling beam/io.c for IRIX.
> Since The OpenGroup defines the struct iovec::iov_base field to be a
> void*, it is illegal to perform pointer arithmetic on it. I'm really
> surprised this didn't show up in GCC or any other compiler.
Good catch!
> -----
> The implied goal here is to increment an address by a certain number
> of bytes, so casting to a char* as follows will allow the compile to
> succeed:
>
> iov->iov_base = (char*)iov->iov_base + skip;
>
This change looks reasonable to me. I might be wrong, but I think this
is what GCC is doing: assuming that void* aritmetic are 1-byte
increments. If not, the code would probably not have worked as
expected. I like the explicit behaviour. If Tuncer Ayaz or one of the
Erlang/OTP devs does not change this into a topic branch, I'd happily
volunteer to make it a topic branch on github.
--
J.
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| Guest |
| Posted: Fri Oct 29, 2010 1:56 pm |
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Guest
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On Fri, Oct 29, 2010 at 3:21 PM, Jesper Louis Andersen
<jesper.louis.andersen@gmail.com> wrote:
>
> This change looks reasonable to me. I might be wrong, but I think this
> is what GCC is doing: assuming that void* aritmetic are 1-byte
> increments. If not, the code would probably not have worked as
> expected. I like the explicit behaviour. If Tuncer Ayaz or one of the
> Erlang/OTP devs does not change this into a topic branch, I'd happily
> volunteer to make it a topic branch on github.
>
It is a GCC extension, see
http://gcc.gnu.org/onlinedocs/gcc-4.5.1/gcc/Pointer-Arith.html#Pointer-Arith
which really sets the size of the pointer to 1 byte (thus also
enabling the use of sizeof() in the same vein). It can be made into a
warning with -Wpointer-arith if so desired.
Tuncer suggested that I go ahead, so unless you want to do it, ...
--
J.
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