bug#55657: libgccjit is unusable

[John Kehayias]

Hi everyone,

Found out some useful info and a work around for the original reported issue of 
the simple "hello world" of gccjit not working.


------- Original Message -------
On Tuesday, June 28th, 2022 at 1:16 AM, John Kehayias wrote:

> Hi,
>
> ------- Original Message -------
> On Tuesday, June 28th, 2022 at 12:17 AM, Liliana Marie Prikler wrote:
>
> > Keyword here is "has worked for emacs". I've tried porting the logic
> > from flatwhatson's channel over, but regardless of what I do, it
> > already fails in the configure step of Emacs (in a manner that's
> > reproducible outside as well). Thus, I think this is a bug in
> > libgccjit (or perhaps our packaging of it) that simply happened to be
> > ignored during development of Emacs 28, but no longer in the release.
>
>
> Sorry, I should be extra clear that I mean has in the past and continues to 
> work for Emacs. I've been using emacs-pgtk-native-comp through the 
> flatwhatson channel from well before v28 was released. Currently I'm using 
> emacs-pgtk-native-comp-28.1.50-223.3ddccb5. Everything has built, installed, 
> and run fine for as long as I have been using it. Just in case that was in 
> question, and as a point of reference.
>
> Anyway, I'll try to reproduce when I can (tomorrow likely) what you reported 
> in the first message using this setup, if that is of use.
>

I was able to reproduce the original error, though I used the libgccjit package 
from the flatwhatson channel, at v11.3.0 (along with GCC at that version). For 
good measure, I also used the tutorial at that version, just in case 
https://gcc.gnu.org/onlinedocs/gcc-11.3.0/jit/intro/tutorial01.html  I chose 
this version since that is what emacs-native-comp from that channel is built 
with.

Searching for these error messages of missing libraries/files, I found

https://ref.strikr.io/jit/internals/index.html#environment-variables

and a bug report at https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87808

I didn't dive into the details and I'm not expert here, but it gave me the 
clues to work around it. Seems that where gccjit looks for things has some 
assumptions (bugs?) which we can fix at runtime with:

LIBRARY_PATH=$GUIX_ENVIRONMENT/lib/gcc/x86_64-unknown-linux-gnu/11.3.0:$LIBRARY_PATH
 ./gccjittest

The errors reported before were solved with this LIBRARY_PATH addition of the 
lib/gcc subdirectory. So, the test program runs in

guix shell gcc-toolchain@11 libgccjit@11 --pure

where I compiled to gccjittest following the tutorial directions (no change to 
LIBRARY_PATH).

So, looking at the emacs-native-comp definition in flatwhatson, we can see that 
a phase is used to set LIBRARY_PATH before configure just as I did here: 
https://github.com/flatwhatson/guix-channel/blob/master/flat/packages/emacs.scm#L65

Hope this is helpful and unblocks libgccjit and emacs-native-comp for Guix!

John