Bug#173074: marked as done ([PR libgcj/9078] libffi: problems with uint8 on powerpc)
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and subject line libgcj/9078: libffi: problems with uint8 on powerpc
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Date: Sat, 14 Dec 2002 14:43:15 -0500
From: David Paul BELANGER <dbelan2@CS.McGill.CA>
To: Debian Bug Tracking System <submit@bugs.debian.org>
Subject: problems with uint8 on powerpc
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Package: libffi2
Version: 1:3.2.1-0pre3
Severity: normal
ffi_type_uint8 and other arguments shorter than one word are
not passed in correctly to the function called by ffi_call.
Also, returns values are not passed correctly. For example, instead of
finding the returned byte value where the pointer points to, it is found
at an offset of 3 from the pointer.
This is related to the fact that the powerpc is a big endian machine and
somewhere, bytes need to be moved.
I have included code and output I get on my powerpc machine.
Thanks,
David
-----
#include <stdio.h>
#include <ffi.h>
unsigned char identity(unsigned char c) {
printf("identity: %d\n", c);
return c;
}
int main(void) {
ffi_cif cif;
ffi_type *args[1];
void *values[1];
int b;
unsigned char result;
int i;
args[0] = &ffi_type_uint;
/*
* args[0] = &ffi_type_uint8; - if this type is specified,
* function always receives 0.
*/
b = 24;
values[0] = &b;
if (ffi_prep_cif(&cif, FFI_DEFAULT_ABI, 1,
&ffi_type_uint8, args) != FFI_OK) {
printf("error\n");
return 1;
}
ffi_call(&cif, identity, &result, values);
printf("at result: %d\n", result);
printf("at result + 3: %d\n", *(&result + 3));
/*
for (i = 0; i < sizeof(result); i++) {
printf("byte %d = %d\n", i, *((unsigned char *) &result));
}
*/
return 0;
}
-----
output:
identity: 24
at result: 0
at result + 3: 24
-----
David
-- System Information
Debian Release: testing/unstable
Architecture: powerpc
Kernel: Linux ibou 2.4.20-rc1-ben0 #3 Thu Nov 14 22:24:15 EST 2002 ppc
Locale: LANG=C, LC_CTYPE=C
Versions of packages libffi2 depends on:
ii gcc-3.2-base 1:3.2.1-0pre3 The GNU Compiler Collection (base
ii libc6 2.2.5-14.3 GNU C Library: Shared libraries an
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Received: (at 173074-done) by bugs.debian.org; 16 Mar 2003 17:06:43 +0000
>From doko@cs.tu-berlin.de Sun Mar 16 11:06:42 2003
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From: Matthias Klose <doko@cs.tu-berlin.de>
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Message-ID: <15988.44586.196724.492991@gargle.gargle.HOWL>
Date: Sun, 16 Mar 2003 18:02:34 +0100
To: Jeff Sturm <jsturm@one-point.com>
Cc: 173074-done@bugs.debian.org, gcc-gnats@gcc.gnu.org, <gcc-prs@gcc.gnu.org>,
<gcc-bugs@gcc.gnu.org>, <java-prs@gcc.gnu.org>,
David Paul BELANGER <dbelan2@CS.McGill.CA>,
"Prof. Etienne M. Gagnon" <etienne.gagnon@uqam.ca>
Subject: Re: libgcj/9078: libffi: problems with uint8 on powerpc
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Ok, closing the Debian report. Leave the gnats entry to Jeff.
Prof. Etienne M. Gagnon writes:
> On Sun, Mar 16, 2003 at 05:15:47PM +0100, Matthias Klose wrote:
> > hmm, you didn't open this report. Sure I can close it?
>
> Yes, I am sure. The bug was opened by of the developers of the
> SableVM project, and he forwarded to me the information in the Debian
> BTS and in the upstream BTS. Based on that information, I went back
> into the SableVM source code and fixed the bug. It was definitely not
> a libffi bug (yet one has to very carfully read the libffi
> documentation to notice the inconsistency in the treatment of function
> arguments and return values).
Jeff Sturm writes:
> On Sat, 28 Dec 2002, Matthias Klose wrote:
> > ffi_type_uint8 and other arguments shorter than one word are
> > not passed in correctly to the function called by ffi_call.
>
> For an ffi_type_uint8, ffi_call expects the corresponding value
> pointer to be a (unsigned char *). So this is correct usage:
>
> int b = 24;
> args[0] = &ffi_type_uint;
> values[0] = &b;
>
> Also correct would be:
>
> unsigned char b = 24;
> args[0] = &ffi_type_uint8;
> values[0] = &b;
>
> > Also, returns values are not passed correctly. For example, instead of
> > finding the returned byte value where the pointer points to, it is found
> > at an offset of 3 from the pointer.
>
> Return values are handled a little differently than arguments.
> libffi/README says:
>
> RVALUE is a pointer to a chunk of memory that is to hold the
> result of the function call. Currently, it must be
> at least one word in size (except for the n32 version
> under Irix 6.x, which must be a pointer to an 8 byte
> aligned value (a long long). It must also be at least
> word aligned (depending on the return type, and the
> system's alignment requirements). If RTYPE is
> &ffi_type_void, this is ignored. If RVALUE is NULL,
> the return value is discarded.
>
> So this cannot work:
>
> unsigned char result;
> if (ffi_prep_cif(&cif, FFI_DEFAULT_ABI, 1,
> &ffi_type_uint8, args) != FFI_OK) {
>
> You could use "unsigned int result" on a 32-bit target, or use ffi_arg
> which is typedef'ed to work correctly on 32 or 64-bit targets:
>
> ffi_arg result;
> if (ffi_prep_cif(&cif, FFI_DEFAULT_ABI, 1,
> &ffi_type_uint8, args) != FFI_OK) {
>
> With those changes your example should be portable to any target supported
> by libffi.
>
> Jeff
>
>
> --
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