Defining and exporting and a variable undefined in a foreach loop cause a Segmentation fault with Make 4.2.1 on Debian bullseye/sid x64

[Xavier Sanchez]

Hi, I've got a segfault in __strlen_avx2 () at
../sysdeps/x86_64/multiarch/strlen-avx2.S:65

While defining a variable that has been undefined in a foreach loop using Make
4.2.1 on my Bullseye/sid workstation.

The code is a bit tricky. I've attached the Makefile and the backtrace.

# Bug in GNU Make 4.2.1
#
# defining a variable that has been undefined in a foreach loop produce a
# segfault on X64 machine.
#
# Disabling export avoid the sefault
export

# As same as disabling this define
DISCARD_ENV := templates from script format
define discard_env
$(foreach var,$(DISCARD_ENV),$(eval undefine $(var)))
endef

ARTIFACTS := build/a build/b

# In this situation: defining a variable that has been undefined
# in the foreach loop befaure causes the segfault:
templates := t1.tpl t2.tpl # <----
format := qcow2

.PHONY: all
all: $(ARTIFACTS)

$(ARTIFACTS):
@echo $@

gdb.txt
Description: Text document

Makefile
Description: Text document