[PATCH][4.15] crypto: adjust rijndaelEncrypt() prototype for gcc11

[Jan Beulich <jbeulich@xxxxxxxx>]

The upcoming release complains, not entirely unreasonably:

In file included from rijndael.c:33:
.../xen/include/crypto/rijndael.h:55:53: note: previously declared as 'const 
unsigned char[]'
   55 | void    rijndaelEncrypt(const unsigned int [], int, const unsigned char 
[],
      |                                                     
^~~~~~~~~~~~~~~~~~~~~~
rijndael.c:865:8: error: argument 4 of type 'u8[16]' {aka 'unsigned char[16]'} 
with mismatched bound [-Werror=array-parameter=]
  865 |     u8 ct[16])
      |     ~~~^~~~~~
In file included from rijndael.c:33:
.../xen/include/crypto/rijndael.h:56:13: note: previously declared as 'unsigned 
char[]'
   56 |             unsigned char []);
      |             ^~~~~~~~~~~~~~~~

While it's not really clear to me why it would complain only for arg 4,
the adjustment to make is obvious and riskfree also for arg 3: Simply
declare the correct array dimension right away. This then allows
compilers to apply checking at call sites, which seems desirable anyway.

For the moment I'm leaving untouched the disagreement between u8/u32
used in the function definition and unsigned {char,int} used in the
declaration, as making this consistent would call for touching further
functions.

Reported-by: Charles Arnold <carnold@xxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
There are quite a few more issues with gcc11, but from my brief initial
inspection I'm suspecting (hoping) it'll rather be the compiler which
will get further changed by the time their release gets finalized. Just
one example:

.../xen/include/xen/string.h:101:27: error: '__builtin_memcmp' specified bound 
4 exceeds source size 0 [-Werror=stringop-overread]
  101 | #define memcmp(s1, s2, n) __builtin_memcmp(s1, s2, n)
      |                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~
mpparse.c:722:13: note: in expansion of macro 'memcmp'
  722 |         if (memcmp(mpf->mpf_signature, "_MP_", 4) == 0 &&
      |             ^~~~~~

Clearly neither the 1st nor the 2nd argument have a "source size" of 0.

--- a/xen/include/crypto/rijndael.h
+++ b/xen/include/crypto/rijndael.h
@@ -52,7 +52,7 @@
 
 int    rijndaelKeySetupEnc(unsigned int [], const unsigned char [], int);
 int    rijndaelKeySetupDec(unsigned int [], const unsigned char [], int);
-void   rijndaelEncrypt(const unsigned int [], int, const unsigned char [],
-           unsigned char []);
+void   rijndaelEncrypt(const unsigned int [], int, const unsigned char [16],
+           unsigned char [16]);
 
 #endif /* __RIJNDAEL_H */