[Qemu-devel] ARM page crossing inside insn? (Re: ARM ethernet fixes)

[Antti P Miettinen <ananaza@iki.fi>]

Antti P Miettinen <ananaza@iki.fi> writes:
> Looks like the kernel somehow ends up thinking that we are loading
> something from zero. Hmm.. the value being loaded to r1 is zero. So
> could this be related to crossing a page boundary in the middle of an
> instruction? But anyway - I'll try to debug this further..

Looks like it might be the page crossing. The below little program is
a  bit smaller test case. Without args, no segfault, with arg it
segfaults (inside ARM sysemu - at least for me):

#include <stdio.h>
#include <string.h>

long buf[8192/4];

int
main(int ac, char **av)
{
    unsigned long base = (unsigned long)(void *)(buf + 4096/4);
    unsigned long dummy;

    if (ac > 1)
    {
	base &= ~0xfff;
	base -= 4;
    }
    printf("buf: %p, base: 0x%08lx, dummy: 0x%08lx\n", buf, base, dummy);
    __asm__ __volatile__ ("ldmia %0,{%1,%2}"
			  : "=r" (base) : "0" (base), "r" (dummy));
    printf("base: 0x%08lx, dummy: 0x%08lx\n", base, dummy);
    return 0;
}

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