[ping] Re: jit and cross-compilers (use and configuration).

[Iain Sandoe <iain@sandoe.co.uk>]

Hi Dave,

Note: this does cause a build break for cross compilers with —enable-languages=all  (if the linkers for host and target have different command line options used in the build)

(it is not a serious break, one can exclude jit by manually listing all the other languages)

- nevertheless, it would be good to establish if there is a meaningful use-case for libgccjit in a cross-compiler, and if so fix the configuration - or (if no meaningful use-case) exclude it as per the patch.

thanks
Iain

> On 26 Jun 2022, at 14:06, Iain Sandoe <iain@sandoe.co.uk> wrote:
> 
> 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) … but I’m 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’m not sure if these would work as currently implemented)
> 
> ----
> 
> It’s 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 —enable-languages=all (and most Darwin platform versions default to host_shared).  So I’d like to see what the best way forward is …..
> 
> ----
> 
> In the short-term there are some issues with the configuration for cross-compilers…
> 
> 1) the values queried in gcc/jit/Make-lang.in relate to the ‘ld’ 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) .. 
> 
> … another is to find a way to fix the configuration to pick up suitable values for $host (although I’m not sure how much of that we have readily available, since usually libtool is doing that work).
> 
> thoughts?
> cheers
> Iain
> 
> <0001-configure-Disable-jit-for-cross-compilers.patch>