Just spent two hours chasing down why recent 2.6.2-rc1 kernels don't
boot.
It turns out that find_next_bit() returns 0 under "qemu-fast" and
"qemu" where it returns 32 under "qemu-i386" and native x86.
Bedtime for me, but here's the offending code:
/**
* find_first_bit - find the first set bit in a memory region
* @addr: The address to start the search at
* @size: The maximum size to search
*
* Returns the bit-number of the first set bit, not the number of the byte
* containing a bit.
*/
static __inline__ int xfind_first_bit(const unsigned long *addr, unsigned size)
{
int d0, d1;
int res;
/* This looks at memory. Mark it volatile to tell gcc not to move it
around */
__asm__ __volatile__(
"xorl %%eax,%%eax\n\t"
"repe; scasl\n\t"
"jz 1f\n\t"
"leal -4(%%edi),%%edi\n\t"
"bsfl (%%edi),%%eax\n"
"1:\tsubl %%ebx,%%edi\n\t"
"shll $3,%%edi\n\t"
"addl %%edi,%%eax"
:"=a" (res), "=&c" (d0), "=&D" (d1)
:"1" ((size + 31) >> 5), "2" (addr), "b" (addr));
return res;
}
/**
* find_next_bit - find the first set bit in a memory region
* @addr: The address to base the search on
* @offset: The bitnumber to start searching at
* @size: The maximum size to search
*/
static __inline__ int xfind_next_bit(const unsigned long *addr, int size, int
offset)
{
const unsigned long *p = addr + (offset >> 5);
int set = 0, bit = offset & 31, res;
if (bit) {
/*
* Look for nonzero in the first 32 bits:
*/
__asm__("bsfl %1,%0\n\t"
"jne 1f\n\t"
"movl $32, %0\n"
"1:"
: "=r" (set)
: "r" (*p >> bit));
if (set < (32 - bit))
return set + offset;
set = 32 - bit;
p++;
}
/*
* No set bit yet, search remaining full words for a bit
*/
res = xfind_first_bit (p, size - 32 * (p - addr));
return (offset + set + res);
}
int main()
{
unsigned long map = 1;
printf("find_next_bit of %lu = %i\n",
map, xfind_next_bit(&map, 32, 1));
return 0;
}
--
Anyone who quotes me in their sig is an idiot. -- Rusty Russell.