Re: [PATCH v2] build: Option for building all tools in a single binary

[Alex Deymo]

Hi again,

Sorry for the delay with this patch. Here is patch v7 attached.

*** symlinks vs shebangs:

* Other projects use symlinks to have a multicall binary; including busybox
and toolbox which cover similar functionality as coreutils; but not limited
to them: lvm (vgcreate, pvcreate, etc), xz (xzcat, unxz point to "xz") and
others I'm not aware of.

* People using symlinks do not protect against the symlink to symlink case;
they just rely on argv[0]. symlink to symlink is not the only way to
provide a different argv[0]; you can pass whatever you want as the first
argument of argv when you call exec().

* The scheme to follow symlinks to determine which one was the last symlink
requires to accurately reproduce the path search algorithm used by exec()
on the platform we are running; and requires the make a couple of syscalls
just to know what's the tool to call, yet still doesn't solve the whole
case.

* Shebangs allow you to have a symlink to them and it still works without
extra work. On some systems, we can change the value of /proc/$PID/cmdline
and other files to not break use cases like "killall foo" or the result of
"ps".


In general, if you want to use --enable-single-binary is because size is a
concern; and in those cases you know your environment (you are deploying an
embedded system with a particular kernel). You might not care about 4MB in
a multi GB linux distro and there's people out there still doing symlink to
symlink that eventually will get their scripts right; but not yet.

So, I added an option where you can choose at configure time if you want to
install symlinks or shebangs (--enable-single-binary=shebangs for example).
I tested this patch on the ChromiumOS builders and it worked (we managed to
build a builder environment and images for amd64, x86 and arm).

In the shebang case, the program will attempt to modify /proc/$PID/cmdline
by using prctl() if available. There are other ways to modify argv[] on
other platforms (look at the sendmail or postgresql case for example), so
eventually we should migrate that functionality to a gnulib file and make
it work on all the supported platforms... but for now, you still have the
choice to use symlinks if that works for you.

Let me know if you have other questions about this patch and happy canada
day for the canadians out there on this list.

deymo.

single-binary_v7.patch
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