On 5.4.2012 15:11, Jakub Jermar wrote:
> Anyway, I am going to make myself a small SPARC sample and see...
Ok, here are the results:
#include <libarch/ddi.h>
#include <stdint.h>
typedef struct {
uint8_t a;
uint32_t b;
} __attribute__ ((packed)) my_regs_t;
uint32_t main(int argc, char **argv)
{
my_regs_t *regs = (void *) argv;
return *((ioport32_t *) ®s->b);
}
Produces this:
00000000000040e0 <main>:
40e0: d0 02 60 01 ld [ %o1 + 1 ], %o0 ; 32-bit access
40e4: 81 c3 e0 08 retl
40e8: 01 00 00 00 nop
40ec: 30 68 00 05 b,a %xcc, 4100 <exit>
Modifying the return statement to read like this:
return *((uint32_t *) ®s->b);
gives us the following output:
00000000000040e0 <main>:
40e0: c6 0a 60 01 ldub [ %o1 + 1 ], %g3 ; 8-bit access
40e4: c2 0a 60 02 ldub [ %o1 + 2 ], %g1 ; 8-bit access
40e8: c4 0a 60 03 ldub [ %o1 + 3 ], %g2 ; 8-bit access
40ec: 87 28 f0 18 sllx %g3, 0x18, %g3
40f0: 83 28 70 10 sllx %g1, 0x10, %g1
40f4: d0 0a 60 04 ldub [ %o1 + 4 ], %o0 ; 8-bit access
40f8: 85 28 b0 08 sllx %g2, 8, %g2
40fc: 82 10 40 03 or %g1, %g3, %g1
4100: 82 10 80 01 or %g2, %g1, %g1
4104: 81 c3 e0 08 retl
4108: 90 12 00 01 or %o0, %g1, %o0
I think what helps in the first example is both the cast to a volatile
qualified type and also the reference operator. Note that changing the
example as follows, gives us a bad result too:
#include <libarch/ddi.h>
#include <stdint.h>
typedef struct {
ioport8_t a;
ioport32_t b;
} __attribute__ ((packed)) my_regs_t;
uint32_t main(int argc, char **argv)
{
my_regs_t *regs = (void *) argv;
return regs->b;
}
00000000000040e0 <main>:
40e0: c6 0a 60 01 ldub [ %o1 + 1 ], %g3
40e4: c2 0a 60 02 ldub [ %o1 + 2 ], %g1
40e8: c4 0a 60 03 ldub [ %o1 + 3 ], %g2
40ec: 87 28 f0 18 sllx %g3, 0x18, %g3
40f0: 83 28 70 10 sllx %g1, 0x10, %g1
40f4: d0 0a 60 04 ldub [ %o1 + 4 ], %o0
40f8: 85 28 b0 08 sllx %g2, 8, %g2
40fc: 82 10 40 03 or %g1, %g3, %g1
4100: 82 10 80 01 or %g2, %g1, %g1
4104: 81 c3 e0 08 retl
4108: 90 12 00 01 or %o0, %g1, %o0
On the other hand, using pio_read_32() helps again:
return pio_read_32(®s->b);
00000000000040e0 <main>:
40e0: d0 02 60 01 ld [ %o1 + 1 ], %o0
40e4: 81 43 e0 09 membar #StoreStore|#LoadLoad
40e8: 81 c3 e0 08 retl
40ec: 91 32 20 00 srl %o0, 0, %o0
40f0: 30 68 00 04 b,a %xcc, 4100 <exit>
Now, what do we conclude from it?
Jakub
_______________________________________________
HelenOS-devel mailing list
[email protected]
http://lists.modry.cz/cgi-bin/listinfo/helenos-devel
