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How I solved a cryptic Emacs dumping error

on emacs, fix, compilation, unix

Background

While I was trying to compile Emacs to test a fix, I ran into a compilation error. This error occurred during Emacs’ dump phase and it said:

unexec: not enough room for load commands for new __DATA segments (increase headerpad_extra in configure.in to at least 1488)

I followed this error’s advice and I kept increasing the value for headerpad_extra in configure.ac. But each time I did so, it still kept throwing the same error, just with different values like 1638, 13F8, 1518, etc. I eventually doubled the value of headerpad_extra to 2000, but no luck. I eventually realized that bumping this value would do no good, so I searched around for a solution.

Initially, I didn’t find much. I found old mailing list threads for unrelated issues, as well as bug reports for package managers. I also guessed that the error might have something to do with my OS, which is macOS Mojave at the time of this writing, but adding this to my search terms did not help.

The Fix

Finally, by sheer luck, I stumbled upon a Japanese messageboard thread which had a fix for this error:

LDFLAGS = -headerpad_max_install_names ./configure [your options go here]

I decided to export the LDFLAGS for the entire compilation process (just to be safe):

$ export LDFLAGS=-headerpad_max_install_names
$ echo $LDFLAGS
-headerpad_max_install_names
$ ./configure --with-modules --enable-mac-app --prefix=/Applications/Emacs.app/Contents/Resources && make install

And lo and behold, it worked. No more strange dumping errors. I figured that since this error was difficult to solve and the only fix I found was on an obscure Japanese messageboard, it might be a good idea to document this problem in a better format and in English.

Out of curiosity as to why this works, here’s an excerpt from man ld:

     -headerpad_max_install_names
                 Automatically adds space for future expansion of load commands such that all paths could expand to MAXPATHLEN.
                 Only useful if intend to run install_name_tool to alter the load commands later.

This still doesn’t explain it completely and I’m not 100% sure as to what was wrong here and why this solution worked, but it did so I’m not complaining.