Constify a number of accesses in aesni to avoid cast-qual warnings

[dim]

Summary

When testing with clang 3.6.0, I got a number of the following -Wcast-qual warnings (just a few shown):

sys/crypto/aesni/aesni_ghash.c:279:27: error: cast from 'const unsigned char *' to '__attribute__((__vector_size__(2 * sizeof(long long)))) long long *' drops const qualifier [-Werror,-Wcast-qual]
        __m128i *KEY = (__m128i*)key;
                                 ^
sys/crypto/aesni/aesni_ghash.c:292:33: error: cast from 'const unsigned char *' to '__attribute__((__vector_size__(2 * sizeof(long long)))) long long *' drops const qualifier [-Werror,-Wcast-qual]
                Y = _mm_loadu_si128((__m128i*)ivec);
                                              ^
sys/crypto/aesni/aesni_ghash.c:321:39: error: cast from 'const unsigned char *' to '__attribute__((__vector_size__(2 * sizeof(long long)))) long long *' drops const qualifier [-Werror,-Wcast-qual]
                        tmp1 = _mm_loadu_si128(&((__m128i*)ivec)[i]);
                                                           ^
sys/crypto/aesni/aesni_ghash.c:351:38: error: cast from 'const unsigned char *' to '__attribute__((__vector_size__(2 * sizeof(long long)))) long long *' drops const qualifier [-Werror,-Wcast-qual]
                tmp1 = _mm_loadu_si128(&((__m128i*)addt)[i*4]);
                                                   ^
sys/crypto/aesni/aesni_ghash.c:352:38: error: cast from 'const unsigned char *' to '__attribute__((__vector_size__(2 * sizeof(long long)))) long long *' drops const qualifier [-Werror,-Wcast-qual]
                tmp2 = _mm_loadu_si128(&((__m128i*)addt)[i*4+1]);
                                                   ^

In all cases I could find in aesni_ghash.c, it is no problem to use const casts, and declare a few specific variables as const, to fix all these warnings.

No functional change.

Test Plan

Compile and boot.

[dim]

Added one additional const cast in aesni_wrap.c.

[kib]

It is fine with me, but I am not an author of the code.

[jmg]

actually, I consider this a bug in clang.. requiring to cast a point to add const is stupid.. I understand requiring to remove it, but adding const should not generate a warning… This just adds const for no benefit and no change..

So, no, I reject the change…

I was originally fine w/ the _wrap.c but not the _ghash.c as all the _ghash.c code is copied from the white paper, and making minor changes like these creates excessive diffs, but this case is just wrong...

[dim]

I think clang is perfectly right about these warnings, since you *are* dropping const qualifiers. But if you don't want this change, we'll just disable -Wcast-qual for aesni instead.

[jmg]

Sorry, I'll accept the _wrap.c change, but would prefer not to change _ghash.c as it's contributed code…

Sorry for the misunderstanding on what was happening.. I had this compiling cleanly, and am surprised that this is a new error/warning, and did not expect that we'd get this new error/warning when we've previously had such aggressive warnings..

[dim]

In D1726#12, @jmg wrote:

Sorry, I'll accept the _wrap.c change, but would prefer not to change _ghash.c as it's contributed code…

Sorry for the misunderstanding on what was happening.. I had this compiling cleanly, and am surprised that this is a new error/warning, and did not expect that we'd get this new error/warning when we've previously had such aggressive warnings..

This is a result from building the kernel in the projects/clang360-import branch. In previous versions, clang did not have a -Wcast-qual warning, but it was now implemented before 3.6.0, and it catches more instances of dropping qualifiers than gcc does (or at least, version 4.2.1 which we have in base).

In this case, it is apparently easier to just not warn about const dropping, since it is not important for the code, and since it is (partially) contributed.

I would have had to add support for disabling such warnings in the kernel anyway, sooner or later, so I might as well put it in now. That also requires no changes to sys/crypto/aesni, just a few minor additions to the Makefiles.