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  1. 18 Oct, 2007 11 commits
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    • David S. Miller's avatar
      [MATH-EMU]: Fix underflow exception reporting. · 64840966
      David S. Miller authored 
      The underflow exception cases were wrong.

This is one weird area of ieee1754 handling in that the underflow
behavior changes based upon whether underflow is enabled in the trap
enable mask of the FPU control register.  As a specific case the Sparc
V9 manual gives us the following description:

--------------------
If UFM = 0:     Underflow occurs if a nonzero result is tiny and a
                loss of accuracy occurs.  Tininess may be detected
                before or after rounding.  Loss of accuracy may be
                either a denormalization loss or an inexact result.

If UFM = 1:     Underflow occurs if a nonzero result is tiny.
                Tininess may be detected before or after rounding.
--------------------

What this amounts to in the packing case is if we go subnormal,
we set underflow if any of the following are true:

1) rounding sets inexact
2) we ended up rounding back up to normal (this is the case where
   we set the exponent to 1 and set the fraction to zero), this
   should set inexact too
3) underflow is set in FPU control register trap-enable mask

The initially discovered example was "DBL_MIN / 16.0" which
incorrectly generated an underflow.  It should not, unless underflow
is set in the trap-enable mask of the FPU csr.

Another example, "0x0.0000000000001p-1022 / 16.0", should signal both
inexact and underflow.  The cpu implementations and ieee1754
literature is very clear about this.  This is case #2 above.

However, if underflow is set in the trap enable mask, only underflow
should be set and reported as a trap.  That is handled properly by the
prioritization logic in

arch/sparc{,64}/math-emu/math.c:record_exception().

Based upon a report and test case from Jakub Jelinek.
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
Signed-off-by: default avatarAdrian Bunk <bunk@kernel.org>
      64840966
    • Mark Fortescue's avatar
      [SPARC32]: Fix rounding errors in ndelay/udelay implementation. · eb845a0b
      Mark Fortescue authored 
      __ndelay and __udelay have not been delayung >= specified time.
The problem with __ndelay has been tacked down to the rounding of the
multiplier constant. By changing this, delays > app 18us are correctly
calculated.
The problem with __udelay has also been tracked down to rounding issues.
Changing the multiplier constant (to match that used in sparc64) corrects
for large delays and adding in a rounding constant corrects for trunctaion
errors in the claculations.
Many short delays will return without looping. This is not an error as there
is the fixed delay of doing all the maths to calculate the loop count.
Signed-off-by: default avatarMark Fortescue <mark@mtfhpc.demon.co.uk>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
Signed-off-by: default avatarAdrian Bunk <bunk@kernel.org>
      eb845a0b
    • Alexander Shmelev's avatar
      [SPARC32]: Fix bug in sparc optimized memset. · 7380487e
      Alexander Shmelev authored 
      Sparc optimized memset (arch/sparc/lib/memset.S) does not fill last
byte of the memory area, if area size is less than 8 bytes and start
address is not word (4-bytes) aligned.

Here is code chunk where bug located:
/* %o0 - memory address, %o1 - size, %g3 - value */
8:
     add    %o0, 1, %o0
    subcc    %o1, 1, %o1
    bne,a    8b
     stb %g3, [%o0 - 1]

This code should write byte every loop iteration, but last time delay
instruction stb is not executed because branch instruction sets
"annul" bit.

Patch replaces bne,a by bne instruction.

Error can be reproduced by simple kernel module:

--------------------
#include <linux/module.h>
#include <linux/config.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <string.h>

static void do_memset(void **p, int size)
{
        memset(p, 0x00, size);
}

static int __init memset_test_init(void)
{
    char fooc[8];
    int *fooi;
    memset(fooc, 0xba, sizeof(fooc));

    do_memset((void**)(fooc + 3), 1);

    fooi = (int*) fooc;
    printk("%08X %08X\n", fooi[0], fooi[1]);

    return -1;
}

static void __exit memset_test_cleanup(void)
{
    return;
}

module_init(memset_test_init);
module_exit(memset_test_cleanup);

MODULE_LICENSE("GPL");
EXPORT_NO_SYMBOLS;
--------------------
Signed-off-by: default avatarAlexander Shmelev <ashmelev@task.sun.mcst.ru>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
Signed-off-by: default avatarAdrian Bunk <bunk@kernel.org>
      7380487e
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