Re: Passing `-B', `-isystem' and `-Wl,dynamic-linker' flags

[ludo at gnu dot org (Ludovic Courtès)]

Hi,

ludo@gnu.org (Ludovic Courtès) writes:

> Thus, when building GCC, `-B' and `-isystem' flags must be passed so
> that it finds the libc headers, as well as a `-Wl,-dynamic-linker' flag
> to pass the path to the dynamic linker.  However, none of the
> environment variables supposedly honored by `configure' seem to suffice
> to propagate these flags through all the GCC build tree and all the
> build stages (currently, NixOS GCC builds circumvent this problems by
> hacking around Makefiles).
>
> What's the recommended way to achieve this?

FWIW, I solved it by passing various environment variables, either at
`configure' time, at `make' time, or both.  Namely:

  1. I passed `CFLAGS_FOR_BUILD' and `LDFLAGS_FOR_BUILD' with the
     relevant `-B', `-isystem' and `-Wl,-dynamic-linker' flags to the
     top-level `configure'.

  2. I then ran `make' with

       make BOOT_LDFLAGS="-B/path/to/libc/lib \
                          -Wl,-dynamic-linker=/path/to/libc/lib/ld-linux.so.2" \
            C_INCLUDE_PATH="$PWD/prev-gcc/include:$PWD/prev-gcc/include-fixed:/path/to/libc/include" \
            CPPFLAGS="-DSSIZE_MAX=LONG_MAX"

     Not all parts of the build require these flags, but it doesn't hurt
     to pass them from the beginning.  The `CPPFLAGS' setting works
     around the fact that GCC ended up using its own <limits.h> (under
     `prev-gcc/include-fixed'), which doesn't define `SSIZE_MAX'.

This is somewhat kludgey and inconvenient, maybe redundant, but I
couldn't find any better way.

One complication is that some environment variables are captured and
substituted by `config.status', while others are only read by makefiles
(and sometimes then captured by a sub-`configure'), making step (2)
above unavoidable.

Thanks,
Ludovic.