Problem with Canadian cross (was: Re: Error building libgcc: missing setting for CPP)

[Paul Smith <psmith@xxxxxxx>]

On Sun, 2012-01-22 at 11:59 -0800, Ian Lance Taylor wrote:
> In an ordinary build, ORIGINAL_AS_FOR_TARGET will be set
> to /usr/bin/as, and similarly for LD and NM.  PLUGIN_LD will typically
> be the same as LD.
> 
> You said you are building a cross-compiler; make sure that you build
> and install a cross-binutils first.

Thanks for this; I found a silly mistake in my process and got much
farther.

So here is what I want to do.  Maybe this is stupid.  I need to generate
a GCC tool suite that will run on much older versions of GNU/Linux on
32bit Intel systems (call it OLDSYS).  I'm performing the builds of the
tool suite on a newer GNU/Linux Intel 64bit system and I don't have a
complete OLDSYS system available to use as a build machine.  Finally, I
want the output of the compiler, when I invoke it, to support both 32bit
and 64bit Intel embedded environments (call that NEWSYS).  I have a
sysroot for OLDSYS, and I have another sysroot for NEWSYS.

So, my thought was to first create a "cross-compiler" from whatever the
native GNU/Linux system is to OLDSYS, then use that as part of a
Canadian cross to get the "cross-compiler" I want: runs on OLDSYS,
generates code (via a sysroot) for NEWSYS including both 32bit and
64bit.

The odd thing is that these are all GNU/Linux Intel systems and so
they're actually somewhat compatible, but the idea of the Canadian cross
still seems valid to me... no?


So I first created a cross-compiler for OLDSYS, configuring binutils
(2.22) and gcc (4.6.2) with --target=OLDSYS --with-sysroot=OLDSYSROOT
(and building and installing into a separate directory of course).

Then I started trying to create the Canadian cross, configuring binutils
and GCC with --host=OLDSYS --target=NEWSYS --with-sysroot=NEWSYSROOT.

When I do this, I can see it finding the OLDSYS compiler I built
previously, and binutils configures and builds fine and if I check, the
resulting binary is indeed a 32bit version and runs fine on OLDSYS.

And, gcc appears to be working fine, for a while.  Then I get this
error:

  OLDSYS-gcc    -g -O2 -DIN_GCC -DCROSS_DIRECTORY_STRUCTURE -DNATIVE_CROSS \
    -W [...] -DHAVE_CONFIG_H -o cpp gcc.o o [...] \
    ../libcpp/libcpp.a ../libiberty/libiberty.a ../libdecnumber/libdecnumber.a
  NEWSYS-gcc -dumpspecs > tmp-specs
  /bin/sh: NEWSYS-gcc: command not found
  Makefile:1852: recipe for target `specs' failed
  make[4]: *** [specs] Error 127
  make[4]: Leaving directory `/usr/src/gcc/obj-base/gcc/gcc'
  Makefile:5279: recipe for target `all-gcc' failed
  make[3]: *** [all-gcc] Error 2
  make[3]: Leaving directory `/usr/src/gcc/obj-base/gcc'
  Makefile:898: recipe for target `all' failed
  make[2]: *** [all] Error 2
  make[2]: Leaving directory `/usr/src/gcc/obj-base/gcc'

You can see that here we're trying to invoke NEWSYS-gcc which doesn't
exist yet and so it's failing.

Looking at gcc/Makefile I see that it's using GCC_FOR_TARGET and that
it's set properly:

  # The GCC to use for compiling crt*.o.
  # Usually the one we just built.
  # Don't use this as a dependency--use $(GCC_PASSES).
  GCC_FOR_TARGET = $(STAGE_CC_WRAPPER) ./xgcc -B./ [...]
	...
  # Dump a specs file to make -B./ read these specs over installed ones.
  $(SPECS): xgcc$(exeext)
          $(GCC_FOR_TARGET) -dumpspecs > tmp-specs
          mv tmp-specs $(SPECS)

That looks right: it uses ./xgcc.  However, in the top-level makefile I
see this:

  # If GCC_FOR_TARGET is not overriden on the command line, then this
  # variable is passed down to the gcc Makefile, where it is used to
  # build libgcc2.a.  We define it here so that it can itself be
  # overridden on the command line.
  GCC_FOR_TARGET=$(STAGE_CC_WRAPPER) NEWSYS-gcc

And, we pass this values down to the sub-makes on the command line (via
the $(EXTRA_GCC_FLAGS) variable) which overrides the settings in those
makefiles.

I don't know how this got here.  I didn't set GCC_FOR_TARGET myself;
just those configure flags.  It's not in my environment.  When configure
goes looking for these binaries it clearly realizes they're not there
(from the top-level config.log):

  configure:9916: checking for NEWSYS-gcc
  configure:9946: result: no

(along with all the other tools: NEWSYS-ld, etc.)  But then later on I
see it setting all the *_FOR_TARGET values to use the NEWSYS-prefixed
values.

When I look at the configuration for building OLDSYS (a straightforward
cross-compile), the top-level Makefile also sets GCC_FOR_TARGET but it
uses this value, which works OK:

  GCC_FOR_TARGET=$(STAGE_CC_WRAPPER) $$r/$(HOST_SUBDIR)/gcc/xgcc -B$$r/$(HOST_SUBDIR)/gcc/


Why did my other configure decide to use something different?  Any ideas
on where to look?  Thanks!