Re: [PATCH v2] test-lib.sh: Use GLIBC_TUNABLES instead of MALLOC_CHECK_ on glibc >= 2.34

Elia Pinto [off-list ref] writes:

Compared to the first version, the code has been simplified, based on Junio's
indications, introducing some redundancy in the setting of the glibc variables
covered by the patch

I think we can even lose the separate case statement and write its
body inside if/then...fi.  The following shows the result of
shuffling the lines to do so.

 	setup_malloc_check () {
+		if _GLIBC_VERSION=$(getconf GNU_LIBC_VERSION 2>/dev/null) &&
+		   _GLIBC_VERSION=${_GLIBC_VERSION#"glibc "} &&
+		   expr 2.34 \<= "$_GLIBC_VERSION" >/dev/null

I am wondering if we want to make sure "getconf" returned a string
that begins with "glibc " before stripping that prefix.  Hopefully
such a paranoia is probably unneeded.

+		then
+			g=
+			LD_PRELOAD="libc_malloc_debug.so.0"
+			for t in \
+				glibc.malloc.check=1 \
+				glibc.malloc.perturb=165
+			do
+				g="${g##:}:$t"

Cute.  As this strips a constant, we do not need to be ##greedy
and using just a single # would suffice, right?

+			done
+			GLIBC_TUNABLES=$g
+			export LD_PRELOAD GLIBC_TUNABLES
+			;;
+		fi
 		MALLOC_CHECK_=3	MALLOC_PERTURB_=165
 		export MALLOC_CHECK_ MALLOC_PERTURB_
 	}
 	teardown_malloc_check () {
 		unset MALLOC_CHECK_ MALLOC_PERTURB_
+		unset LD_PRELOAD GLIBC_TUNABLES
 	}
 fi

especially the teardown side unsets these unconditionally.