Another possibility to check for and guard against bugs in the use of
@code{malloc}, @code{realloc} and @code{free} is to set the environment
variable @code{MALLOC_CHECK_}. When @code{MALLOC_CHECK_} is set to a
-non-zero value, a special (less efficient) implementation is used which
-is designed to be tolerant against simple errors, such as double calls
-of @code{free} with the same argument, or overruns of a single byte
-(off-by-one bugs). Not all such errors can be protected against,
-however, and memory leaks can result.
+non-zero value less than 4, a special (less efficient) implementation is
+used which is designed to be tolerant against simple errors, such as
+double calls of @code{free} with the same argument, or overruns of a
+single byte (off-by-one bugs). Not all such errors can be protected
+against, however, and memory leaks can result.
Any detected heap corruption results in immediate termination of the
process.
This tunable supersedes the @env{MALLOC_CHECK_} environment variable and is
identical in features.
-Setting this tunable to a non-zero value enables a special (less
+Setting this tunable to a non-zero value less than 4 enables a special (less
efficient) memory allocator for the @code{malloc} family of functions that is
designed to be tolerant against simple errors such as double calls of
free with the same argument, or overruns of a single byte (off-by-one