Hi Ard,

I love your patch! Perhaps something to improve:

[auto build test WARNING on arm/for-next]
[also build test WARNING on v4.20-rc5]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Ard-Biesheuvel/ARM-smp-add-support-for-per-task-stack-canaries/20181209-033321
base:   git://git.armlinux.org.uk/~rmk/linux-arm.git for-next
config: arm-allmodconfig (attached as .config)
compiler: arm-linux-gnueabi-gcc (Debian 7.2.0-11) 7.2.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        GCC_VERSION=7.2.0 make.cross ARCH=arm 

All warnings (new ones prefixed by >>):

   lib/test_ubsan.c: In function 'test_ubsan_vla_bound_not_positive':
>> lib/test_ubsan.c:48:2: warning: ISO C90 forbids variable length array 'buf' [-Wvla]
     char buf[size];
     ^~~~
   lib/test_ubsan.c: In function 'test_ubsan_out_of_bounds':
>> lib/test_ubsan.c:64:2: warning: ISO C90 forbids variable length array 'arr' [-Wvla]
     volatile int arr[i];
     ^~~~~~~~

vim +/buf +48 lib/test_ubsan.c

854686f4 Jinbum Park 2018-04-10  44  
854686f4 Jinbum Park 2018-04-10  45  static void test_ubsan_vla_bound_not_positive(void)
854686f4 Jinbum Park 2018-04-10  46  {
854686f4 Jinbum Park 2018-04-10  47  	volatile int size = -1;
854686f4 Jinbum Park 2018-04-10 @48  	char buf[size];
854686f4 Jinbum Park 2018-04-10  49  
854686f4 Jinbum Park 2018-04-10  50  	(void)buf;
854686f4 Jinbum Park 2018-04-10  51  }
854686f4 Jinbum Park 2018-04-10  52  
854686f4 Jinbum Park 2018-04-10  53  static void test_ubsan_shift_out_of_bounds(void)
854686f4 Jinbum Park 2018-04-10  54  {
854686f4 Jinbum Park 2018-04-10  55  	volatile int val = -1;
854686f4 Jinbum Park 2018-04-10  56  	int val2 = 10;
854686f4 Jinbum Park 2018-04-10  57  
854686f4 Jinbum Park 2018-04-10  58  	val2 <<= val;
854686f4 Jinbum Park 2018-04-10  59  }
854686f4 Jinbum Park 2018-04-10  60  
854686f4 Jinbum Park 2018-04-10  61  static void test_ubsan_out_of_bounds(void)
854686f4 Jinbum Park 2018-04-10  62  {
854686f4 Jinbum Park 2018-04-10  63  	volatile int i = 4, j = 5;
854686f4 Jinbum Park 2018-04-10 @64  	volatile int arr[i];
854686f4 Jinbum Park 2018-04-10  65  
854686f4 Jinbum Park 2018-04-10  66  	arr[j] = i;
854686f4 Jinbum Park 2018-04-10  67  }
854686f4 Jinbum Park 2018-04-10  68  

:::::: The code at line 48 was first introduced by commit
:::::: 854686f4edf483db1e0d26d972bdb8fb65c8bfaa lib: add testing module for UBSAN

:::::: TO: Jinbum Park <jinb.park7@gmail.com>
:::::: CC: Linus Torvalds <torvalds@linux-foundation.org>

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