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Some versions of gcc (observed with gcc 4.8.5 in CentOS 7) will report
spurious build_assert() failures for some assertions about structure
layouts. There is no clear pattern as to what causes these spurious
failures, and the build assertion does succeed in that no unresolvable
symbol reference is generated in the compiled code.
Adjust the assertions to work around these apparent compiler issues.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
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We currently implement build-time assertions via a mechanism that
generates a call to an undefined external function that will cause the
link to fail unless the compiler can prove that the asserted condition
is true (and thereby eliminate the undefined function call).
This assertion mechanism can be used for conditions that are not
amenable to the use of static_assert(), since static_assert() will not
allow for proofs via dead code elimination.
Add __attribute__((error(...))) to the undefined external function, so
that the error is raised at compile time rather than at link time.
This allows us to provide a more meaningful error message (which will
include the file name and line number, as with any other compile-time
error), and avoids the need for the caller to specify a unique symbol
name for the external function.
Change the name from linker_assert() to build_assert(), since the
assertion now takes place at compile time rather than at link time.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
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Reset the accumulated authentication state when cipher_setiv() is
called, to allow the cipher to be reused without resetting the key.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
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The GCM cipher mode of operation (in common with other counter-based
modes of operation) has a notion of blocksize that does not neatly
fall into our current abstraction: it does operate in 16-byte blocks
but allows for an arbitrary overall data length (i.e. the final block
may be incomplete).
Model this by adding a concept of alignment size. Each call to
encrypt() or decrypt() must begin at a multiple of the alignment size
from the start of the data stream. This allows us to model GCM by
using a block size of 1 byte and an alignment size of 16 bytes.
As a side benefit, this same concept allows us to neatly model the
fact that raw AES can encrypt only a single 16-byte block, by
specifying an alignment size of zero on this cipher.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
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Signed-off-by: Michael Brown <mcb30@ipxe.org>
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