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Re: [Qemu-devel] qemu 0.5.1 emulation bug?
From: |
Herbert Poetzl |
Subject: |
Re: [Qemu-devel] qemu 0.5.1 emulation bug? |
Date: |
Sat, 24 Jan 2004 18:45:16 +0100 |
User-agent: |
Mutt/1.4.1i |
On Sun, Jan 25, 2004 at 01:09:52AM +1100, Rusty Russell wrote:
> Just spent two hours chasing down why recent 2.6.2-rc1 kernels don't
> boot.
hum, interesting, 2.6.2-rc1 is booting here, with
the 'to be tested' cvs version ... (5.2 rc)
best,
Herbert
> 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.
>
>
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