Re: [Valgrind-users] VG_(pread) and Bad ELF magic number

[Tom H. <to...@co...>]

On 14/08/09 14:43, John Reiser wrote:
>> pread64(3, "\177ELF\1\2\1\0\0\0\0\0\0\0\0\0\0\2\0\24\0\0\0\1\20\0 "..., 4096, 0) = 4096
>> pread64(3, "\177ELF\1\2\1\0\0\0\0\0\0\0\0\0\0\2\0\24\0\0\0\1\20\0 "..., 4096, 0) = 4096
>
> --------------------------------------------------------------------------^^^^-------^^^^
>
> [versus]
>
>> pread64(3, "\177ELF\1\2\1\0\0\0\0\0\0\0\0\0\0\2\0\24\0\0\0\1\20\0 "..., 4096, 0) = 4096
>> pread64(3, "\335\335\335\335\335\335\335\335\335\335\335\335\335\335"..., 52, 0) = 52
>
> ----------------------------------------------------------------------------^^-------^^
>
>
>> Except for the geteuid(), stat64() and fstat64(), there seems to be no  difference.
>
> The second call to pread64 has a third argument of 52 instead of 4096.

Which should be fine of course - it just means we're only asking for the 
first 52 bytes of the file instead of the first 4096 bytes. As far as I 
know there is no requirement for the size or offset given to pread to be 
page aligned or anything like that so both should work.

It might of course explain why the test program is not showing the problem.

I still reckon this is a kernel bug, although it may well be the change 
in the count that triggers it.

Tom

-- 
Tom Hughes (to...@co...)
http://www.compton.nu/