[PATCH] taskset: fix non-fancy cpuset printing on big-endian
Arnout Vandecappelle
arnout at mind.be
Mon Jan 4 19:10:33 UTC 2016
ping
On 01-12-15 13:52, Arnout Vandecappelle (Essensium/Mind) wrote:
> The non-fancy version of the from_cpuset uses CPU_SETSIZE as if it
> represents the number of bytes in the cpuset, while it is actually
> the number of bits. This leads to out-of-bounds accesses on the
> cpu_set_t in the big-endian case. Basically all uses of CPU_SETSIZE
> have to be divided by 8. This is done correctly in the fancy version
> of from_cpuset.
>
> In addition, the big-endian case is completely wrong to begin with.
> All standard C libraries that I know of implement cpu_set_t as an
> unsigned long array, so both for big and little endian, the least
> significant bits are in the beginning of the array. Therefore, the
> approach taken for the little endian case is equally valid. We only
> need special handling for big endian when CPU_SETSIZE is large and
> we use an unsigned long long to get more bits out.
>
> Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout at mind.be>
> ---
> miscutils/taskset.c | 35 ++++++++++++++++++-----------------
> 1 file changed, 18 insertions(+), 17 deletions(-)
>
> diff --git a/miscutils/taskset.c b/miscutils/taskset.c
> index 100b1d9..18a4b67 100644
> --- a/miscutils/taskset.c
> +++ b/miscutils/taskset.c
> @@ -75,27 +75,28 @@ static char *from_cpuset(cpu_set_t *mask)
> #define TASKSET_PRINTF_MASK "%llx"
> static unsigned long long from_cpuset(cpu_set_t *mask)
> {
> - char *p = (void*)mask;
> + BUILD_BUG_ON((CPU_SETSIZE/8) < sizeof(int));
>
> - BUILD_BUG_ON(CPU_SETSIZE < sizeof(int));
> -
> - /* Take the least significant bits. Careful!
> - * Consider both CPU_SETSIZE=4 and CPU_SETSIZE=1024 cases
> + /* Take the least significant bits. Assume cpu_set_t is
> + * implemented as an array of unsigned long or unsigned
> + * int.
> */
> + if ((CPU_SETSIZE/8) < sizeof(long))
> + return *(unsigned*)mask;
> + if ((CPU_SETSIZE/8) < sizeof(long long))
> + return *(unsigned long*)mask;
> #if BB_BIG_ENDIAN
> - /* For big endian, it means LAST bits */
> - if (CPU_SETSIZE < sizeof(long))
> - p += CPU_SETSIZE - sizeof(int);
> - else if (CPU_SETSIZE < sizeof(long long))
> - p += CPU_SETSIZE - sizeof(long);
> - else
> - p += CPU_SETSIZE - sizeof(long long);
> + if (sizeof(unsigned long long) > sizeof(unsigned long)) {
> + /* We can put two long in the long long, but they have to
> + * be swapped: the least significant word comes first in the
> + * array */
> + unsigned long *p = (void*)mask;
> + return (unsigned long long)*p +
> + ((unsigned long long)*(p+1) << (8*sizeof(unsigned long)));
> + }
> +#else
> + return *(unsigned long long*)mask;
> #endif
> - if (CPU_SETSIZE < sizeof(long))
> - return *(unsigned*)p;
> - if (CPU_SETSIZE < sizeof(long long))
> - return *(unsigned long*)p;
> - return *(unsigned long long*)p;
> }
> #endif
>
>
--
Arnout Vandecappelle arnout dot vandecappelle at essensium dot com
Senior Embedded Software Architect . . . . . . +32-478-010353 (mobile)
Essensium, Mind division . . . . . . . . . . . . . . http://www.mind.be
G.Geenslaan 9, 3001 Leuven, Belgium . . . . . BE 872 984 063 RPR Leuven
LinkedIn profile: http://www.linkedin.com/in/arnoutvandecappelle
GPG fingerprint: 7493 020B C7E3 8618 8DEC 222C 82EB F404 F9AC 0DDF
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