[Bug driver/65294] New: No easy way of setting default Mac OS X target - darwin_minversion not enough

[astrand at cendio dot se]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65294

            Bug ID: 65294
           Summary: No easy way of setting default Mac OS X target -
                    darwin_minversion not enough
           Product: gcc
           Version: 4.6.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: driver
          Assignee: unassigned at gcc dot gnu.org
          Reporter: astrand at cendio dot se

Host: i686-pc-linux-gnu
Build: i686-pc-linux-gnu
Target: x86_64-apple-darwin10
Mac OS X SDK: 10.6

We want to configure GCC so that OS X 10.6 is the default target. For this, we
changed DARWIN_MINVERSION_SPEC to be "10.6". This seemed to work -
__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ is 1060. However, we later then
realized that calling gcc with -mmacosx-version-min=10.6 gave a different
behaviour. For example, in the latter case, ld is called with
-no_compact_unwind. In other words, changing DARWIN_MINVERSION_SPEC /
%(darwin_minversion) to say 10.6 causes GCC to run with a split personality,
where some parts thinks it's 10.4 and others thinks it's 10.6. 

In order to solve this, either a lot of spec logics needs to be changed, or the
-mmacosx-version-min argument needs to be "faked". This is actually done when
the environment variable MACOSX_DEPLOYMENT_TARGET is found - but not when cross
compiling. Any good reason for this? 

Also, it seems to me that DARWIN_MINVERSION_SPEC / %(darwin_minversion) is not
that useful, when most of the specs are checking the -mmacosx-version-min
argument anyway. 

The patch from gkeating
(https://gcc.gnu.org/ml/gcc-patches/2007-02/msg01484.html) had the explicit
goal of "fix or avoid a bunch of bugs where one part or another of the
toolchain differed from the compiler in the minimum system version to be
targetted.", but this is exactly the problem we are seeing here, thus I believe
some additional work is required.