L4Re, BUILD_ARCH, cross-building for ARM on MIPS

[Adam Lackorzynski]

Hi Paul,

On Mon Jun 10, 2019 at 16:50:57 +0200, Paul Boddie wrote:
> In attempting to investigate building L4Re/Fiasco.OC for the Raspberry Pi 
> Zero, I encountered an unusual problem: unusual because, I suppose, most 
> people do not try and cross-build on architectures other than x86(-64).
> 
> When performing the initial L4Re build directory initialisation step...
> 
> make B=mybuild
> 
> ...BUILD_ARCH seems to be set to x86 even on other architectures. This then 
> causes CCXX_FLAGS to be populated with x86-dependent settings such as -m32, 
> and the gcc host compilers for MIPS raise errors upon encountering these 
> unrecognised arguments.
> 
> Here is the offending command in the top-level Makefile (line 376 in my 
> version, r83 in Subversion):
> 
> GENDEP_OUTPUT=$$X.out $(CC) $(CCXX_FLAGS) -c $$X -o $$X.o
> 
> Although it seemed like the config step could be performed after ignoring 
> these errors, I did wonder if there might be some undesirable consequences. In 
> the end, I found that the following invocation was needed:
> 
> make B=mybuild CC=gcc CXX=g++ LD=ld BUILD_ARCH=mips CPU=32r2 CPU_ABI=32
> 
> After that, things seem to work as expected. I imagine that there is a 
> "chicken and egg" situation here: the appropriate settings would be obtained 
> from the configuration, but the command being run sets up the configuration.
> 
> Has anyone else seen this problem before?

That's a good point. You can do "make B=builddir T=arm-rv" to
immediately switch to the target architecture. I'm trying to improve the
handling here as I just stumpled into this in a different setting as
well.


HTH,
Adam