gnu makefile: shell function execution order in a recipe - makefile

Question

I'm using $(shell ...) gnu make function in a Makefile recipe, and it runs first before the preceding rows. Why?
A very simple example:
.PHONY: all
all:
#echo 1
#echo $(eval a=$(shell echo 2a 1>&2))2b
#echo 3 $(a)
The output is:
2a
1
2b
3
First runs the $(shell ...) line (2a), then the other lines.
How can I manage to run the $(shell ...) function when its row runs in the recipe, in this order?
1
2a
2b
3
Edit:
Without $(shell ...) it works as I expected:
.PHONY: all
all:
#echo 1
$(eval a=a)
#echo 2 $(a)
$(eval a=b)
#echo 3 $(a)
Output:
1
2 a
3 b
Edit 2:
Here is a part of the original Makefile. The pieces at >>> show the essence of my problem: I want to put the output of udisksctl into a make variable instead of file $#.loop (and do the same with $#.mount).
$(HDIMG): $(BOOTBLOCK_MBR_BIN) $(BOOTBLOCK_EXT2_BIN) $(LOADER_BIN) | $(DESTDIR)
dd if=/dev/zero of=$#.ext2 bs=1 seek=$(PSIZEB) count=0 2>/dev/null
$(MKFSEXT2) -F $#.ext2 >/dev/null
dd if=$(word 2,$^) of=$#.ext2 conv=notrunc 2>/dev/null
cp $< $#
dd if=/dev/zero of=$# bs=1 seek=$(HDSIZEB) count=0 2>/dev/null
echo $(PFDISK) | $(TR) | $(FDISK) $# >/dev/null
dd if=$#.ext2 of=$# bs=512 seek=$(PSTART) conv=sparse,notrunc iflag=fullblock 2>/dev/null
>>> udisksctl loop-setup --file $# --offset $(PSTARTB) --size $(PSIZEB) >$#.loop
sed -i -e 's/.* //;s/\.//' $#.loop
cat $#.loop
>>> udisksctl mount --block-device $$(cat $#.loop) >$#.mount
sed -i -e 's/.* //;s/\.//' $#.mount
cat $#.mount
#
mkdir -p $$(cat $#.mount)/boot/
cp $(word 2,$^) $$(cat $#.mount)/boot/
#/sbin/filefrag -b512 -e /
#
udisksctl unmount --block-device $$(cat $#.loop)
udisksctl loop-delete --block-device $$(cat $#.loop)
rm $#.loop

Answer 1

When make runs a recipe, it first expands all variables/functions in it, and then runs the shell commands line by line.
You can work around that by executing every shell command with $(shell ...), or, in your case, by using $(info ...) instead of echo:
.PHONY: all
all:
$(info 1)
$(info $(eval a=$(shell echo 2a 1>&2))2b)
$(info 3 $(a))
Output:
1
2a
2b
3
make: Nothing to be done for 'all'.
The Nothing to be done for 'all'. part is caused by the fact that after expanding the functions, the recipe is effectively empty (has 0 shell commands). Adding a no-op command (e.g. #true) to it removes the message.