align-check.c

#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>

#ifdef __SANITIZE_ADDRESS__
#define ALLOC_STACK(ptr) __asan_describe_address(ptr)
#else
#define ALLOC_STACK(ptr) fprintf(stderr,                                       \
    "Do an ASAN build to get allocation stacks.\n");
#endif

#define DUMP_IF_NOT_ALIGNED(ptr, align)                                        \
  if ((((uintptr_t)ptr + align - 1) & ~(align - 1)) != (uintptr_t)ptr) {       \
    fprintf(stderr, "%s does not satisfy alignment request of %d.\n",          \
            #ptr, align);                                                      \
    ALLOC_STACK(ptr);                                                          \
  }

int main() {
  char * meh = malloc(128);

  DUMP_IF_NOT_ALIGNED(meh, 16);
  DUMP_IF_NOT_ALIGNED(&(meh[7]), 16);
  DUMP_IF_NOT_ALIGNED(&(meh[16]), 16);

  free(meh);

  return 0;
}

trace

repositories/test-valgrind  » gcc -fsanitize=address -fno-omit-frame-pointer -g align-check.c
repositories/test-valgrind  » ./a.out 
&(meh[7]) does not satisfy alignment request of 16.
0x60180000bf87 is located 7 bytes inside of 128-byte region [0x60180000bf80,0x60180000c000)
allocated by thread T0 here:
    #0 0x7fb030bbd45a (/usr/lib/x86_64-linux-gnu/libasan.so.0.0.0+0x1545a)
    #1 0x4008de (/home/padenot/src/repositories/test-valgrind/a.out+0x4008de)
    #2 0x7fb030801de4 (/lib/x86_64-linux-gnu/libc-2.17.so+0x21de4)
repositories/test-valgrind  » addr2line ./a.out 0x4008de
??:0
/home/padenot/src/repositories/test-valgrind/align-check.c:20