Hi,

This is another consequence of a change Apple has introduced with macOS11 which 
is the SDK version now changes on every incremental OS update. So updating from 
11.0 to 11.1 (and I presume Xcode 12.3) you now have SDK 11.1, not 11.0, and 
thus the current build of gcc, which has the sys root to the 11.0 baked into 
it, now fails.

A quick workaround is to set in your shell SDKROOT to point to the new path to 
the 11.1 SDK. I use

export SDKROOT=`xcrun --show-sdk-path`

in my ~/.profile which does this for each shell.

This is almost certainly not the only issue this change in SDK versioning is 
going to cause, and its likely going to take a while to figure out what to do 
in MacPorts. One option, for ports which have this problem is to configure them 
to use the versionless SDK path at configuration time, at least on macOS 11 and 
newer… This has other issues, but for now it seems the lesser evil to me…

Chris

> On 15 Dec 2020, at 9:23 pm, Andreas Skarlatoudis via macports-users 
> <macports-users@lists.macports.org> wrote:
> 
> Hello all, 
> 
> I’m working on a MBP, 2018 model and yesterday I updated to the latest 
> version of BigSur. Since then I cannot compile any fortran code and the error 
> I get is 
> 
> ld: library not found for -lSystem
> collect2: error: ld returned 1 exit status
> 
> 
> I have tried both gcc9 and gcc10
> 
> gfortran -v gives this output :
> 
> Using built-in specs.
> COLLECT_GCC=gfortran
> COLLECT_LTO_WRAPPER=/opt/local/libexec/gcc/x86_64-apple-darwin20/10.2.0/lto-wrapper
> Target: x86_64-apple-darwin20
> Configured with: 
> /opt/local/var/macports/build/_opt_bblocal_var_buildworker_ports_build_ports_lang_gcc10/gcc10/work/gcc-10.2.0/configure
>  --prefix=/opt/local --build=x86_64-apple-darwin20 
> --enable-languages=c,c++,objc,obj-c++,lto,fortran,jit 
> --libdir=/opt/local/lib/gcc10 --includedir=/opt/local/include/gcc10 
> --infodir=/opt/local/share/info --mandir=/opt/local/share/man 
> --datarootdir=/opt/local/share/gcc-10 --with-local-prefix=/opt/local 
> --with-system-zlib --disable-nls --program-suffix=-mp-10 
> --with-gxx-include-dir=/opt/local/include/gcc10/c++/ --with-gmp=/opt/local 
> --with-mpfr=/opt/local --with-mpc=/opt/local --with-isl=/opt/local 
> --enable-stage1-checking --disable-multilib --enable-lto 
> --enable-libstdcxx-time --with-build-config=bootstrap-debug 
> --with-as=/opt/local/bin/as --with-ld=/opt/local/bin/ld 
> --with-ar=/opt/local/bin/ar --with-bugurl=https://trac.macports.org/newticket 
> <https://trac.macports.org/newticket> --enable-host-shared --disable-tls 
> --with-pkgversion='MacPorts gcc10 10.2.0_4' 
> --with-sysroot=/Library/Developer/CommandLineTools/SDKs/MacOSX11.0.sdk
> Thread model: posix
> Supported LTO compression algorithms: zlib
> gcc version 10.2.0 (MacPorts gcc10 10.2.0_4) 
> 
> I’ve removed and reinstalled MacPorts and all packages but it didn’t help.
> 
> Any ideas what may be the problem here? 
> 
> Thanks in advance for your help
> 
> Andreas 
> 
> Dr. Seismologist
> 

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