tree 9318cd5bdc2c6c879bc6eb05d019d862be71ac1a
parent fbb9837ad56e327f22c6b155e7b2fce796723e33
author Hanno Becker <hanno.becker@arm.com> 1498480018 +0100
committer Hanno Becker <hanno.becker@arm.com> 1498480545 +0100

Prevent clever optimization to prematurely quit loop in safe memcmp

The previous version of `mbedtls_ssl_safer_memcmp` did not qualify the
pointers to the arrays to be compared as volatile, theoretically
opening the possibility for the compiler to notice that the loop
operation `diff |= A[i] ^ B[i]` is pointless if `diff = -1`. This
commit changes this. It also declares the stack variable `diff` as
volatile, to force read and write in every loop; omitting that, the
compiler would still be allowed to get away with reading `A[i]` and
`B[i]` but not doing the XOR and not updating `diff`.