>>> On 3/21/2013 at 12:20 AM, in message <[email protected]>,
Michael Brown <[email protected]> wrote:
> On 20/03/13 08:34, Bo Yang wrote:
> > Signed-off-by: Bo Yang<[email protected]>
> > ---
> > src/arch/i386/include/bits/byteswap.h | 4 ++--
> > 1 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/src/arch/i386/include/bits/byteswap.h
> b/src/arch/i386/include/bits/byteswap.h
> > index f3d30a2..0d9cb96 100644
> > --- a/src/arch/i386/include/bits/byteswap.h
> > +++ b/src/arch/i386/include/bits/byteswap.h
> > @@ -53,8 +53,8 @@ __bswap_variable_64 ( uint64_t x ) {
> > static inline __attribute__ (( always_inline )) void
> > __bswap_64s ( uint64_t *x ) {
> > struct {
> > - uint32_t low;
> > - uint32_t high;
> > + uint32_t __attribute__ (( may_alias )) low;
> > + uint32_t __attribute__ (( may_alias )) high;
> > } __attribute__ (( may_alias )) *dwords = ( ( void * ) x );
> > uint32_t discard;
>
> I'm puzzled by this; as far as I know, the may_alias which is already
> present on the structure type should be sufficient. I have tested gcc
> versions 4.3.0, 4.3.1, 4.3.2, 4.3.3, 4.3.4 and 4.3.5 (using the GCC
> compile farm) and have not been able to reproduce any problem with the
> original, unmodified code.
>
> Could you let me know precisely which gcc version is causing problems,
> and what the error message is?
I am sorry that I missed the architecture. gcc 4.3 on x86. My testing
uses gcc 4.3.4 on x86 system(SLES11SP2).
I don't understand this either. :( It looks like that the 32-bit gcc 4.3 does
some optimization and checks into the structure. Here is the message:
arch/i386/include/bits/byteswap.h:61: error: likely type-punning may break
strict-aliasing rules: object ‘*{unknown}’ of main type ‘unsigned int’ is
referenced at or around arch/i386/include/bits/byteswap.h:61 and may be aliased
to object ‘test64’ of main type ‘long long unsigned int’ which is referenced at
or around tests/byteswap_test.c:83.
arch/i386/include/bits/byteswap.h:61: error: likely type-punning may break
strict-aliasing rules: object ‘*{unknown}’ of main type ‘unsigned int’ is
referenced at or around arch/i386/include/bits/byteswap.h:61 and may be aliased
to object ‘test64’ of main type ‘long long unsigned int’ which is referenced at
or around tests/byteswap_test.c:83.
Thanks!
>
> Thanks,
>
> Michael
>
>
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