Like built-in.a, the command length of the *.mod rule scales with the depth of the directory times the number of objects in the Makefile. Add $(obj)/ by the shell command (awk) instead of by Make's builtin function. In-tree modules still have some room to the limit (ARG_MAX=2097152), but this is more future-proof for big modules in a deep directory. For example, you can build i915 as a module (CONFIG_DRM_I915=m) and compare drivers/gpu/drm/i915/.i915.mod.cmd with/without this commit. The issue is more critical for external modules because the M= path can be very long as Jeff Johnson reported before [1]. [1] https://lore.kernel.org/linux-kbuild/4c02050c4e95e4cb8cc04282695f8404@codeaurora.org/
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| @@ -275,8 +275,10 @@ $(obj)/%.o: $(src)/%.c $(recordmcount_source) FORCE · 274 unmodified lines | ||
| 275 | 275 | $(call if_changed_rule,cc_o_c) |
| 276 | 276 | $(call cmd,force_checksrc) |
| 277 | 277 | |
| 278 | −cmd_mod = echo $(addprefix $(obj)/, $(call real-search, $*.o, .o, -objs -y -m)) | \ | |
| 279 | − $(AWK) -v RS='( |\n)' '!x[$$0]++' > $@ | |
| 278 | +# To make this rule robust against "Argument list too long" error, | |
| 279 | +# ensure to add $(obj)/ prefix by a shell command. | |
| 280 | +cmd_mod = echo $(call real-search, $*.o, .o, -objs -y -m) | \ | |
| 281 | + $(AWK) -v RS='( |\n)' '!x[$$0]++ { print("$(obj)/"$$0) }' > $@ | |
| 280 | 282 | |
| 281 | 283 | $(obj)/%.mod: FORCE |
| 282 | 284 | $(call if_changed,mod) |