build legacy-support for an older OS than the host OS?

[René J.V. Bertin]

On Tuesday June 03 2025 21:26:18 Fred Wright wrote:

Thanks!

>2a) Set SDKROOT to point to the target SDK.

I of course ended up trying my hand at this, and actually succeeding for 10.7. I used this addition in the legacy-support port:

# set host_os_version ${macosx_deployment_target}
# variant sdk10.7 description {build as if on OS X 10.7} {}
# if {[variant_isset sdk10.7]} {
#     set macosx_deployment_target    10.7
#     configure.sdk_version           ${macosx_deployment_target}
#     set extraflags          -D__MPLS_TARGET_OSVER=1070
# }
# if {${host_os_version} ne ${macosx_deployment_target}} {
#     ui_warn "Building for ${configure.sdk_version}!"
#     configure.sdkroot       [portconfigure::configure_get_sdkroot ${configure.sdk_version}]
#     # somehow we need to invoke this twice?!
#     configure.sdkroot       [portconfigure::configure_get_sdkroot ${configure.sdk_version}]
#     set extraflags          "${extraflags} \
#                             -mmacosx-version-min=${macosx_deployment_target} \
#                             -isysroot${configure.sdkroot}"
#     configure.cflags-append   {*}${extraflags}
#     configure.cxxflags-append {*}${extraflags}
#     configure.ldflags-append  {*}${extraflags}
# }

then manually installed the static archive with a version suffix to its name. I wasn't really motivated to risk breaking my entire install by installing the corresponding shared libraries though they'd probably work and just make me use the "backported" versions of a handful of functions that my host 10.9.5 has over 10.7 .

Then, in the port this all started for, I added

# platform darwin {
#     set host_os_version ${macosx_deployment_target}
#     variant sdk10.7 description {build as if on OS X 10.7} {}
#     if {[variant_isset sdk10.7]} {
#         set macosx_deployment_target    10.7
#         configure.sdk_version           ${macosx_deployment_target}
#         legacysupport.use_mp_libcxx     yes
#         # very important: tell the legacysupport headers which OS version we're targetting!
#         set extraflags                  -D__MPLS_TARGET_OSVER=1070
#     }
#     if {${host_os_version} ne ${macosx_deployment_target}} {
#         ui_warn "Building for ${configure.sdk_version}!"
#         configure.sdkroot       [portconfigure::configure_get_sdkroot ${configure.sdk_version}]
#         # somehow we need to invoke this twice?!
#         configure.sdkroot       [portconfigure::configure_get_sdkroot ${configure.sdk_version}]
#         set extraflags          "${extraflags} -mmacosx-version-min=${macosx_deployment_target} \
#                                 -isysroot${configure.sdkroot}"
#         configure.cflags-append   {*}${extraflags}
#         configure.cxxflags-append {*}${extraflags}
#         configure.ldflags-append  {*}${extraflags}
#
#         proc legacysupport::get_library_name {} {
#             global prefix macosx_deployment_target
#             return ${prefix}/lib/libMacportsLegacySupport-${macosx_deployment_target}.a
#         }
#     }
# }
#

and got a proper 10.7 binary. (Full disclosure: I use a hotpatched official rust toolchain, which always sets the min os version to 10.12 so I need vtool to fix that - and had to enable building vtool in port:cctools first).

That binary works ... on 10.9 . I don't think I have yet heard back if it also does on 10.7 but in theory it should esp. since I haven't found any indication that it actually calls any of those functions 10.7 doesn't have.

If ever I were to pursue this more seriously I'd probably add legacy-support supports for a select number of older SDKs, which install just that versioned static archive, and maybe add a convenience procedure to the legacy-support PG  to add the appropriate TARGET_OSVER macro definition to CPPFLAGS.

Re 10.6 : I tried that first. Turns out that this would add a backported function that calls a function (chk_fail or something like that) which is itself unavailable on 10.9 .


R.