Re: [Qemu-devel] [PATCH] configure: Make C++ test work with --enable-werror

[Peter Maydell]

On 24 February 2014 19:08, Peter Maydell <address@hidden> wrote:
> gcc's C++ compiler complains about being passed some -W options
> which make sense for C but not for C++. This means we mustn't try
> a C++ compile with QEMU_CFLAGS, but only with a filtered version
> that removes the offending options. This filtering was already being
> done for uses of C++ in the build itself, but was omitted for the
> "does C++ work?" configure test. This only showed up when doing
> builds which explicitly enabled -Werror with --enable-werror,
> because the "do the compilers work" tests were mistakenly placed
> above the "default werror based on whether compiling from git" code.
> Further, when the test did fail configure would plunge on regardless
> of the error since we were running do_cc in a subshell. Fix this
> complex of errors:
>
> 1. Move the default-werror code up so that there are no invocations
> of compile_object and friends between it and the point where we
> set $werror explicitly based on the --enable-werror command line
> option.
>
> 2. Provide a mechanism for filtering QEMU_CFLAGS to create
> QEMU_CXXFLAGS, and use it for the test we run here.
>
> 3. Provide a do_cxx function to run a test with the C++ compiler
> rather than doing cute tricks with subshells and do_cc.
>
> Signed-off-by: Peter Maydell <address@hidden>
> ---
> This was pretty confusing to debug (mostly because I got tripped
> up by the issue fixed by 1. above)...
>
> We could probably roll do_libtool into do_compiler, but I'd rather
> not mix that cleanup up with this build-breakage fix.

Alas, this won't work for clang builds, because clang
does not like us building a .c file with the C++ compiler,
which the test does.

thanks
-- PMM