It's only relocatable given some assumptions which are violated by various distributions (AIX was already mentioned; and the bin and lib directories may not be next to each other with some distributions' preferred configurations). Basically the configure mechanism gives us some flexibility not otherwise available, without requiring a full build from source (which is fairly involved and requires an existing ghc). On 8/7/20, John Cotton Ericson wrote:

Per https://gitlab.haskell.org/ghc/ghc/issues/17191 I do hope to break up our configure script soon.[1] Then the bindist will need not ship the "entire" configure script, but just what is necessary to fill in the settings file(s) which have that information Ben mentions.

I think that will improve the optics of the situation a bit; for example, I don't think the reduced bindist configure script should need to worry about directories at all since GHC is relocatable (when built by Hadrian).

John

[1]: I will be able to resume work on that once I get to the bottom of https://gitlab.haskell.org/ghc/ghc/merge_requests/1102. All help greatly appreciated!

On 8/7/20 11:15 AM, Ben Gamari wrote:

...

"Mathieu Boespflug" writes:

...

Hi all,

GHC currently has 3 tier-1 platforms: Linux, macOS and Windows. I'll focus the dicussion below on these three platforms. The binary distributions for Linux and macOS are designed to be unpacked, then the user types ./configure && make install. This is not the case for Windows.

On all platforms it's possible to create "relocatable" installations, such that GHC doesn't really care where it's installed, and commands will still work if the install directory changes location on the filesystem. So my question is, why do we have a ./configure step on Linux and macOS? Why could we not have bindists for all platforms that work like the Windows one? I.e. a binary distribution that you just unpack, in any directory of your choice, without any configuration or installation step. There are a few reasons:

* Relocatable GHC builds have only been supported for only a few releases now and only under the Hadrian build system, which is not currently used to produce our binary distributions (hopefully this will change for 9.2).

* On Windows we have the luxury of having a very well-controlled environment as we rely on essentially nothing from the host system. We provide our own mingw toolchain, statically link against libc, and have no additional dynamic dependencies.

By contrast, on Linux we have to deal with a much larger configuration space:

* several linkers, each with their own bugs

* several C compilers, supporting various subsets of functionality and quirks (e.g. some distributions enable -pie by default, others do not)

* various LLVM packaging schemes

Since it would be quite expensive to probe the toolchain characteristics on every compiler invocation, we rather do this once in the configure script during bindist installation and package the result in the installed `settings` file.

* On Linux we may have additional dynamic dependencies (e.g. libdw, numactl) which we check for during configuration time, lest the user be faced with an unsightly linker error if they happen to be missing a library.

In principle we could perhaps avoid the need for many of these checks by creating one binary distribution per operating system distribution. However, we will first need to move to Hadrian to build our binary distributions.

Cheers,

- Ben

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