The problem is that the logic which checks if a pointer is
valid relies on a poor heuristic based on the start and end
addresses of the data segment and heap.

Apart from miscalculating the heap bounds, this approach also
suffers from the fact that memory can come from places other
than the heap. See Bug#58528 for a more detailed explanation.

On Linux, the solution is to access the process's memory
through /proc/self/task/<tid>/mem, which allows for retrieving
the contents of pages within the virtual address space of
the calling process. If a address range is not mapped, a
input/output error is returned.

client/mysqltest.cc:
  Use new interface to my_safe_print_str.
include/my_stacktrace.h:
  Drop name from my_safe_print_str.
mysys/stacktrace.c:
  Access the process's memory through a file descriptor and
  dump the contents of the memory range. The file descriptor
  offset is equivalent to a offset into the address space.
  
  Do not print the name of the variable associated with the
  address. It can be better accomplished at a higher level.
sql/mysqld.cc:
  Put the variable dumping information within its own newline block.
  Use symbolic names which better convey information to the user.