Re: [linux-next:master 952/3956] crypto/blake2b_generic.c:73:13: warning: stack frame size of 9776 bytes in function 'blake2b_compress_one_generic'

On Sat, Jan 16, 2021 at 08:59:50AM +0800, kernel test robot wrote:

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
head:   b3a3cbdec55b090d22a09f75efb7c7d34cb97f25
commit: 28dcca4cc0c01e2467549a36b1b0eacfdb01236c [952/3956] crypto: blake2b - sync with blake2s implementation
config: powerpc64-randconfig-r021-20210115 (attached as .config)
compiler: clang version 12.0.0 (https://github.com/llvm/llvm-project 5b42fd8dd4e7e29125a09a41a33af7c9cb57d144)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # install powerpc64 cross compiling tool for clang build
        # apt-get install binutils-powerpc64-linux-gnu
        # https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=28dcca4cc0c01e2467549a36b1b0eacfdb01236c
        git remote add linux-next https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
        git fetch --no-tags linux-next master
        git checkout 28dcca4cc0c01e2467549a36b1b0eacfdb01236c
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=powerpc64 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <redacted>

All warnings (new ones prefixed by >>):

quoted

quoted

crypto/blake2b_generic.c:73:13: warning: stack frame size of 9776 bytes in function 'blake2b_compress_one_generic' [-Wframe-larger-than=]

   static void blake2b_compress_one_generic(struct blake2b_state *S,
               ^
   1 warning generated.


vim +/blake2b_compress_one_generic +73 crypto/blake2b_generic.c

    48	
    49	#define G(r,i,a,b,c,d)                                  \
    50		do {                                            \
    51			a = a + b + m[blake2b_sigma[r][2*i+0]]; \
    52			d = ror64(d ^ a, 32);                   \
    53			c = c + d;                              \
    54			b = ror64(b ^ c, 24);                   \
    55			a = a + b + m[blake2b_sigma[r][2*i+1]]; \
    56			d = ror64(d ^ a, 16);                   \
    57			c = c + d;                              \
    58			b = ror64(b ^ c, 63);                   \
    59		} while (0)
    60	
    61	#define ROUND(r)                                \
    62		do {                                    \
    63			G(r,0,v[ 0],v[ 4],v[ 8],v[12]); \
    64			G(r,1,v[ 1],v[ 5],v[ 9],v[13]); \
    65			G(r,2,v[ 2],v[ 6],v[10],v[14]); \
    66			G(r,3,v[ 3],v[ 7],v[11],v[15]); \
    67			G(r,4,v[ 0],v[ 5],v[10],v[15]); \
    68			G(r,5,v[ 1],v[ 6],v[11],v[12]); \
    69			G(r,6,v[ 2],v[ 7],v[ 8],v[13]); \
    70			G(r,7,v[ 3],v[ 4],v[ 9],v[14]); \
    71		} while (0)
    72	
  > 73	static void blake2b_compress_one_generic(struct blake2b_state *S,
    74						 const u8 block[BLAKE2B_BLOCK_SIZE])
    75	{
    76		u64 m[16];
    77		u64 v[16];
    78		size_t i;
    79	
    80		for (i = 0; i < 16; ++i)
    81			m[i] = get_unaligned_le64(block + i * sizeof(m[i]));
    82	
    83		for (i = 0; i < 8; ++i)
    84			v[i] = S->h[i];
    85	
    86		v[ 8] = BLAKE2B_IV0;
    87		v[ 9] = BLAKE2B_IV1;
    88		v[10] = BLAKE2B_IV2;
    89		v[11] = BLAKE2B_IV3;
    90		v[12] = BLAKE2B_IV4 ^ S->t[0];
    91		v[13] = BLAKE2B_IV5 ^ S->t[1];
    92		v[14] = BLAKE2B_IV6 ^ S->f[0];
    93		v[15] = BLAKE2B_IV7 ^ S->f[1];
    94	
    95		ROUND(0);
    96		ROUND(1);
    97		ROUND(2);
    98		ROUND(3);
    99		ROUND(4);
   100		ROUND(5);
   101		ROUND(6);
   102		ROUND(7);
   103		ROUND(8);
   104		ROUND(9);
   105		ROUND(10);
   106		ROUND(11);
   107	#ifdef CONFIG_CC_IS_CLANG
   108	#pragma nounroll /* https://bugs.llvm.org/show_bug.cgi?id=45803 */
   109	#endif
   110		for (i = 0; i < 8; ++i)
   111			S->h[i] = S->h[i] ^ v[i] ^ v[i + 8];
   112	}
   113	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

Looks like the clang bug that causes large stack usage in this function
(https://bugs.llvm.org/show_bug.cgi?id=45803 which is still unfixed) got
triggered again.  Note that the function only has 264 bytes of local variables,
so there's no reason why it should use anywhere near 9776 bytes of stack space.

I'm not sure what we can do about this.  Last time the solution was commit
0c0408e86dbe which randomly added a 'pragma nounroll' to the loop at the end.

Anyone have any better idea than randomly trying adding optimization pragmas and
seeing what makes the report go away?

Also this was reported with clang 12.0.0 which is a prerelease version, so I'm
not sure how much I'm supposed to care about this report.

- Eric