Created attachment 77662 [details] [review]
cairo-1.12.12-make-ac-float-endianess-test-llvm-bitcode-save.patch

I've posted this to bugs.gentoo.org before
  https://bugs.gentoo.org/show_bug.cgi?id=464982

As requested there, I repost the patches here. There are two issues I encountered when compiling cairo with "clang -O4":

1) bitcode representation of object files makes float endianess test in configure break (see attached patch)

2) "automatic configuration" of pthreads does not work while explicitly --enable-pthread=yes to configure does

If "--enable-pthread=yes" configure option is not passed, the default is "auto" instead of "yes", which basically runs the first block of the following lines in
  cairo-1.12.12/build/configure.ac.pthread (around line 220)
-- >8 --
    dnl Check if we can use libc's stubs in libcairo.
    dnl Only do this if the user hasn't explicitly enabled
    dnl pthreads, but is relying on automatic configuration.
    have_pthread="no"
    if test "x$enable_pthread" != "xyes"; then
        CAIRO_CHECK_PTHREAD(
            [pthread], [-D_REENTRANT], [],
            [libcairo_pthread_program],
            [have_pthread=yes],
            [])
    fi

    dnl Default to using the real pthreads for libcairo.
    if test "x$have_pthread" != "xyes"; then
        have_pthread="$have_real_pthread";
        pthread_CFLAGS="$real_pthread_CFLAGS";
        pthread_LIBS="$real_pthread_LIBS";
    fi
-- >8 --

This automatic configuration apparently does not work if clang -O4 is used, even though libcairo_pthread_program seems to succeed.

Or in other words: using libc stubs as a pthread provider currently does not work if clang -O4 is in use, the automatically configured stubs make the compile quit with

libtool: link: clang -march=native -pipe -fomit-frame-pointer -O4 -finline-limit=1200 -march=native -pipe -fomit-frame-pointer -O4 -Wl,-O1 -Wl,--hash-style=gnu -Wl,--sort-common -Wl,-z -Wl,norelro -o .libs/cairo-analyse-trace cairo-analyse-trace.o cairo-error.o  -Wl,--as-needed ../util/cairo-script/.libs/libcairo-script-interpreter.so ../util/cairo-missing/.libs/libcairo-missing.a ./.libs/libcairoperf.a ../boilerplate/.libs/libcairoboilerplate.a /var/tmp/paludis/x11-libs-cairo-1.12.12-r1/work/cairo-1.12.12/src/.libs/libcairo.so ../src/.libs/libcairo.so -lpixman-1 -lfontconfig -lfreetype -lEGL -ldl -lpng15 -lxcb-shm -lxcb-render -lxcb -lXrender -lX11 -lXext -lz -lGL -lOpenVG -lrt -lm
/var/tmp/paludis/x11-libs-cairo-1.12.12-r1/work/cairo-1.12.12/src/.libs/libcairo.so: error: undefined reference to 'pthread_mutexattr_settype'
/var/tmp/paludis/x11-libs-cairo-1.12.12-r1/work/cairo-1.12.12/src/.libs/libcairo.so: error: undefined reference to 'pthread_mutexattr_init'
/var/tmp/paludis/x11-libs-cairo-1.12.12-r1/work/cairo-1.12.12/src/.libs/libcairo.so: error: undefined reference to 'pthread_mutexattr_destroy'
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make[4]: *** [cairo-analyse-trace] Error 1
make[4]: Leaving directory `/var/tmp/paludis/x11-libs-cairo-1.12.12-r1/work/cairo-1.12.12/perf'
make[3]: Leaving directory `/var/tmp/paludis/x11-libs-cairo-1.12.12-r1/work/cairo-1.12.12/perf'
make[2]: Leaving directory `/var/tmp/paludis/x11-libs-cairo-1.12.12-r1/work/cairo-1.12.12/perf'
make[3]: *** [all-recursive] Error 1
make[2]: *** [all] Error 2
make[1]: Leaving directory `/var/tmp/paludis/x11-libs-cairo-1.12.12-r1/work/cairo-1.12.12'
make[1]: *** [all-recursive] Error 1
make: *** [all] Error 2



I'm unsure about a proper fix for this, but thought about
  - patch configure.ac.pthread to use real_pthread as an automatic configuration
    i.e. throw out libc stubs, use real_pthread if libcairo_pthread_program 

Thanks