cbuilt-inxlcaltivec

The parameter type is not valid for a function of this linkage type

I'm working on AIX with IBM's XL C compiler. I'm catching a compile error and I'm not sure how to proceed:

$ xlc -g3 -O0 -qarch=pwr8 -qaltivec fips197-p8.c -o fips197-p8.exe
"fips197-p8.c", line 59.16: 1506-754 (W) The parameter type is not valid for a function of this linkage type.

The relevant source code is shown below. The complete source code is available at fips197-p8.c. The source code is a test driver for Power 8 __cipher and __vcipherlast. It has a main and a few C functions. Effectively is a minimal complete working example for Power 8 AES.

$ cat -n fips197-p8.c
...

11  #if defined(__xlc__) || defined(__xlC__)
12  // #include <builtins.h>
13  #include <altivec.h>
14  typedef vector unsigned char uint8x16_p8;
15  typedef vector unsigned int uint64x2_p8;
16  #else
17  #include <altivec.h>
18  typedef vector unsigned char uint8x16_p8;
19  typedef vector unsigned long long uint64x2_p8;
20  #endif
...

52  uint8x16_p8 Load8x16(const uint8_t src[16])
53  {
54  #if defined(__xlc__) || defined(__xlC__)
55          /* IBM XL C/C++ compiler */
56  # if defined(__LITTLE_ENDIAN__)
57          return vec_xl_be(0, src);
58  # else
59          return vec_xl(0, src);
60  # endif
61  #else
62          /* GCC, Clang, etc */
63
64  #endif
65  }

The compiler version is shown below. We don't control the compiler, so this is what we have:

$ xlc -qversion
IBM XL C/C++ for AIX, V13.1.3 (5725-C72, 5765-J07)
Version: 13.01.0003.0000

vec_xl is fine on a little-endian. vec_xl for big-endian is giving us the trouble.

What is the problem, and how do I fix it?

Solution

  • So a little guesswork (confirmed by OP comments since it works) led me to think that this cryptic & obscure "The parameter type is not valid for a function of this linkage type." message (google first match is this question !) could be a qualifier issue.

    Since your contract is 

    uint8x16_p8 Load8x16(const uint8_t src[16])

    it is possible that, given the options & the current endianness, the compiler/prototype believes that vec_xl_be expects a non-const parameter as src.

    So passing a const violates the contract (and that's the nicest way xlc could find to notifu you)

    So either change to

    uint8x16_p8 Load8x16(uint8_t src[16])

    (with the risk of dropping constant constraints for all callers)

    or drop the const by a non-const cast (like we do when the prototype lacks const, but the data is in fact not modified in the function):

    vec_xl_be(0,(uint8_t*)src);