libc/string: add memcpy_from_ci()

This adds memcpy_from_ci, a cache inhibited version of memcpy, required
by secure boot. The secure boot verification code is stored in a secure
ROM and the logic that contains the ROM within the processor is
implemented in a way that it only responds to CI (cache inhibited)
operations. Due to performance issues we copy the verification code from
the secure ROM to RAM and we use memcpy_ci for that.

What makes memcpy_ci vs ordinary memcpy?

memcpy copies data like in the example below and the compiler translates that
to load instructions that are not cache inhibited (e.g. lbzx - load byte and
zero indexed). In other words, the data is cached.

a[i] = b[i]

memcpy_ci copies data using the cache inhibited version of load instructions:
in_8() and in_be32(), both defined in include/io.h. These functions use lbzcix
and lwzcix assembly instructions, respectively. In this case, the data is not
cached as required by the logic that contains the ROM.

*((uint8_t*) destp) = in_8((uint8_t*)srcp);
*((uint32_t*) destp) = in_be32((uint32_t*)srcp)

Signed-off-by: Claudio Carvalho <cclaudio@linux.vnet.ibm.com>
Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>

0 files changed, 0 insertions, 0 deletions