Elia Pinto <gitter.spi...@gmail.com> writes:
> Recent versions of Linux libc (later than 5.4.23) and glibc (2.x)
> include a malloc() implementation which is tunable via environment
> variables. When MALLOC_CHECK_ is set, a special (less efficient)
> implementation is used which 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 bugs). When MALLOC_CHECK_
> is set to 3, a diagnostic message is printed on stderr
> and the program is aborted.
> Setting the MALLOC_PERTURB_ environment variable causes the malloc
> functions in libc to return memory which has been wiped and clear
> memory when it is returned.
> Of course this does not affect calloc which always does clear the memory.
> The reason for this exercise is, of course, to find code which uses
> memory returned by malloc without initializing it and code which uses
> code after it is freed. valgrind can do this but it's costly to run.
> The MALLOC_PERTURB_ exchanges the ability to detect problems in 100%
> of the cases with speed.
> The byte value used to initialize values returned by malloc is the byte
> value of the environment value. The value used to clear memory is the
> bitwise inverse. Setting MALLOC_PERTURB_ to zero disables the feature.
> This technique can find hard to detect bugs.
> It is therefore suggested to always use this flag (at least temporarily)
> when testing out code or a new distribution.
> Signed-off-by: Elia Pinto <gitter.spi...@gmail.com>
> t/test-lib.sh | 6 ++++++
> 1 file changed, 6 insertions(+)
Interesting, but it bothers me to make it enabled unconditionally.
At least, this shouldn't be enabled under GIT_TEST_OPTS=--valgrind, no?
By the way, "export VAR=VAL" all on the same line, even though it is
in POSIX.1, is reported to be unsupported by some shells people care
about, and needs to be corrected to "VAR=VAL" and "export VAR" as
separate commands. I think we saw a patch to fix an instance or two
that snuck in recently.
> diff --git a/t/test-lib.sh b/t/test-lib.sh
> index 78c4286..98c90b0 100644
> --- a/t/test-lib.sh
> +++ b/t/test-lib.sh
> @@ -93,6 +93,12 @@ export GIT_AUTHOR_EMAIL GIT_AUTHOR_NAME
> export GIT_COMMITTER_EMAIL GIT_COMMITTER_NAME
> export EDITOR
> +# Add libc malloc_check and MALLOC_PERTURB test
> +export MALLOC_CHECK_=3
> +export MALLOC_PERTURB_="$( expr \( $$ % 255 \) + 1)"
> # Protect ourselves from common misconfiguration to export
> # CDPATH into the environment
> unset CDPATH
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