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From: Iain Sandoe <iain@sandoe.co.uk>
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Subject: jit and cross-compilers (use and configuration).
Message-Id: <BD4FD2ED-B0EA-40FD-ADB9-DF8ABC21A8F2@sandoe.co.uk>
Date: Sun, 26 Jun 2022 14:06:01 +0100
Cc: GCC Development <gcc@gcc.gnu.org>
To: David Malcolm <dmalcolm@redhat.com>
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Hi Dave, folks,

It seems to me that it is plausible that one could use the JIT in a =
heterogenous system, e.g. an x86_64-linux-host with some kind of =
co-processor which is supported as a GCC target (and therefore can be =
loaded with jit-d code) =E2=80=A6 but I=E2=80=99m not aware of anyone =
actually doing this?

.. is that use case even reasonable given the current implementation?
(I guess there are invocations of the assembler etc. .. I=E2=80=99m not =
sure if these would work as currently implemented)

----

It=E2=80=99s mildly inconvenient that the build for cross compilers =
generally fails for me on Darwin (reason 1 below) since I tend to =
configure by default with =E2=80=94enable-languages=3Dall (and most =
Darwin platform versions default to host_shared).  So I=E2=80=99d like =
to see what the best way forward is =E2=80=A6..

----

In the short-term there are some issues with the configuration for =
cross-compilers=E2=80=A6

1) the values queried in gcc/jit/Make-lang.in relate to the =E2=80=98ld=E2=
=80=99 that is used for $target not the one used for $host.

 - this means that if we are on a $host with an non-binutils-ld and =
building a cross-compiler for a $target that *does* use binutils-ld, the =
configuration selects flags that do not work so that the build fails.
 - of course, things might fail more subtly in the case that there were =
two *different* binutils ld instances.

2) the testsuite obviously does not work.

So .. one possibility is to disable jit for cross-compilers, (patch =
attached) ..=20

=E2=80=A6 another is to find a way to fix the configuration to pick up =
suitable values for $host (although I=E2=80=99m not sure how much of =
that we have readily available, since usually libtool is doing that =
work).

thoughts?
cheers
Iain


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