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Re: [Qemu-devel] KQEMU bus errors

From: Grzegorz Kulewski
Subject: Re: [Qemu-devel] KQEMU bus errors
Date: Sun, 13 Feb 2005 15:51:34 +0100 (CET)

On Sun, 13 Feb 2005, Julian Seward wrote:

On Sunday 13 February 2005 11:13, Jonas Maebe wrote:
On 13 feb 2005, at 10:42, Darryl Dixon wrote:
Most of the references that I can find for a Linux 'Bus error' talk
about unaligned memory accesses.

Indeed. The only way I know of to get a bus error under Linux/x86 from
a user space program, is to turn on the alignment check flag in the
eflags register, followed by an unaligned memory access.

I have a very vague and possibly wrong memory that the another way
to get a bus error is to mmap a file into an area which is too big
for the file, then read/write the area beyond the end of the file.
Or perhaps that was on Solaris.  In any case, it might be worth
checking this isn't somehow related to mmap or use of mmap.

From man mmap(2):

"SIGBUS Attempted access to a portion of the buffer that does not correspond to the file (for example, beyond the end of the file, including the case where another process has truncated the file)."

So this is very probable that the errors are caused by too small limit of tmpfs mounted on /dev/shm.

Grzegorz Kulewski

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