Hi,
While studying the Infiniband drivers if found an interesting line of
code within the preprocessed files from kernel 2.6.14.1:
// 85 "drivers/infiniband/core/mad.c"
entry = (struct ib_mad_port_private *) ((char *)__mptr - (unsigned int)
(&((struct ib_mad_port_private *)0) ->port_list) );
This line is the result of a macro expansion from list.h. I wonder why
it is safe to dereference the NULL-pointer in the second part of the
right side:
(& ((struct ib_mad_port_private *)0) ->port_list) )
GCC translates the expression into the offset of the field port_list as
intended, but doing this involves dereferencing a NULL-pointer
(evaluates to 0). The expression can only be correct if one assumes that
the dereference will be optimized away - why is it safe to assume that?
Any hints would be appreciated!
Regards,
Hendrik
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