OSDev Meaty Skeleton教程中Makefile未调用Shell脚本问题

It looks like the core issue here is incorrect syntax for assigning variables from shell commands in your Makefile. Let's break down the fixes step by step:

1. Correct Variable Assignment Syntax #

Your current code tries to use != inside the $(info) function, which isn't how GNU Make's shell command assignment works. The != operator is meant for assigning the output of a shell command directly to a variable, not embedding it within an info call.

Replace your existing lines with this properly structured code:

# Assign variables using shell command output first
DEFAULT_HOST != ../default-host.sh
HOST ?= $(DEFAULT_HOST)
HOSTARCH != ../target-triplet-to-arch.sh $(HOST)

# Now print the values for debugging
$(info DEFAULT_HOST is $(DEFAULT_HOST))
$(info HOST is $(HOST))
$(info HOSTARCH is $(HOSTARCH))

2. Compatibility with Older Make Versions #

If you're using a version of GNU Make older than 3.82 (the version where != was introduced), use the $(shell) function instead—it works across all modern Make versions:

DEFAULT_HOST := $(shell ../default-host.sh)
HOST ?= $(DEFAULT_HOST)
HOSTARCH := $(shell ../target-triplet-to-arch.sh $(HOST))

$(info DEFAULT_HOST is $(DEFAULT_HOST))
$(info HOST is $(HOST))
$(info HOSTARCH is $(HOSTARCH))

3. Verify Script Paths and Functionality #

• Double-check that the relative paths (../default-host.sh and ../target-triplet-to-arch.sh) are correct from the directory where you run make. If you're running make from the root of your project instead of the lib/ directory, the paths might resolve incorrectly—you could use absolute paths for testing if needed.
• Ensure your target-triplet-to-arch.sh properly handles the input triplet. For example, a basic working version for i686-elf might look like this:

  #!/bin/sh
  case "$1" in
      i686-elf) echo i386 ;;
      x86_64-elf) echo x86_64 ;;
      *) echo "Unknown triplet: $1" >&2; exit 1 ;;
  esac
  

• Confirm both scripts have executable permissions (you mentioned you set this, but it's worth re-checking with chmod +x ../default-host.sh ../target-triplet-to-arch.sh).

4. Debugging Tips #

If variables still aren't populating, try running the scripts directly from the command line to confirm they output the expected values:

../default-host.sh  # Should print "i686-elf"
../target-triplet-to-arch.sh i686-elf  # Should print your target arch (e.g., "i386")

If these commands fail, fix the scripts first before troubleshooting the Makefile.

内容的提问来源于stack exchange，提问作者K. Shores