Re: [Bug-ddrescue] Alignment of I/O buffer for direct disk access could fail on some memory addresses?

[Antonio Diaz Diaz]

Hello again,

Heikki Tauriainen wrote:
> To protect the code from a buffer alignment failure whose occurrence 
> depends on the buffer's address (which is not guaranteed to remain 
> consistent between invocations of the program), I think it would be 
> safer to compute "disp" using unsigned arithmetic on an integral type
> large enough to hold the address of the buffer.

The problem is that the C++ standard does not guarantee that such 
integral type exists in all implementations. 'intptr_t/uintptr_t' are 
optional in C++11 and do not exist in C++03. (The alignment code of 
ddrescue was written in 2005).

I have released version 1.21-pre3 using a cast to 'unsigned long long', 
a type already used by ddrescue that most probably will be able to 
contain the pointer value.


> Alternatively, the program could (as a sanity check) abort with an
> error in case the buffer cannot be adjusted to a multiple of the
> sector size for direct disk access, or give more debug information
> about the failing read(2) requests, instead of failing silently in
> this case.

In a few days I'll add some code to make ddrescue exit on EINVAL and 
report an error.


Thanks again,
Antonio.