How to write numeric expressions in Makefile? - makefile

Question

I want to write statements about Podman in Makefile. A UID mapping is used here. But I found that I was always unable to do numerical calculations.
Below is my Makefile. But here ${uid}+1 and similar operations will become empty strings. How should I solve this problem?
Thanks!
HOST_GEM5 := /mnt/disk/cuiyujie/workspace/workGem5/gem5
SIM := ${HOST_GEM5}/X86/gem5.opt
SHELL := /bin/bash
DOCKER_GEM5 := /usr/local/src/gem5
subuidSize=$(shell $(( $(podman info --format "{{ range .Host.IDMappings.UIDMap }}+{{.Size }}{{end }}" ) - 1 )))
subgidSize=$(shell $(( $(podman info --format "{{ range .Host.IDMappings.GIDMap }}+{{.Size }}{{end }}" ) - 1 )))
uid := $(shell id -u)
gid := $(shell id -g)
DOCKER_DIRS_MAP := \
-v ${HOST_GEM5}/runScripts:${DOCKER_GEM5}/runScripts
MAP_CMD := \
--user ${uid}:${gid} \
--uidmap ${uid}:0:1 \
--uidmap 0:1:${uid} \
--uidmap $(($uid+1)):$(($uid+1)):$(($subuidSize-$uid)) \
--gidmap ${gid}:0:1 \
--gidmap 0:1:${gid} \
--gidmap $(($gid+1)):$(($gid+1)):$(($subgidSize-$gid))
.PHONY: default clean run build
default: build
build:
podman run -it --rm ${DOCKER_DIRS_MAP} --security-opt seccomp=unconfined \
${MAP_CMD} \
gerrie/gem5:v1 "/bin/bash"
clean:
rm -rf ${HOST_GEM5}/build/*

Answer 1

Make always uses /bin/sh as the shell it invokes, both for recipes and for $(shell ...) functions. /bin/sh is a POSIX-conforming shell. The syntax you're using is not POSIX shell syntax: it's special enhanced syntax that is only available in the bash shell.
You can either rewrite your scripting to work in POSIX shells (probably by using the expr program to do the math), or add this to your makefile to tell it you want to use bash instead of /bin/sh:
SHELL := /bin/bash
Note, of course, that your makefile will now no longer work on any system that doesn't have a /bin/bash shell.