[R-SIG-Mac] Linker warnings and error when building R on Apple silicon

[Mikael Jagan]

Hello,

I am running Big Sur on an M1 Mac and trying to build R from sources.
Some system details:

R> sessionInfo()
 > Platform: aarch64-apple-darwin20 (64-bit)
 > Running under: macOS Big Sur 11.6.3

$ clang --version
 > Apple clang version 13.0.0 (clang-1300.0.29.30)
 > Target: arm64-apple-darwin20.6.0

$ /opt/R/arm64/gfortran/bin/gfortran --version
 > GNU Fortran (GCC) 11.0.0 20201219 (experimental)

It has been a few months since I last built R on this machine.
At the time, I was building with LLVM clang rather than Apple clang
to obtain OpenMP support. I was recently nudged about the OpenMP
runtime library made available here:

https://mac.r-project.org/openmp/

which would allow me to build "normally" with Apple clang.
I am trying now to make the switch.

I have installed all of the binaries hosted here

https://mac.r-project.org/bin/darwin20/arm64/

rather than those hosted here

https://mac.r-project.org/libs-arm64/

which I had previously installed. (Though: the first URL is missing
binaries for gfortran, pandoc, tcl, tk, and tkTable. I obtained
these from the second URL. _Both_ URLs are missing a zlib binary,
so I reluctantly obtained zlib from Homebrew.)

Anyway, I'm running into trouble now... I have attached my
config.site, config.log, and build.out (from 'make >&') ...
config.log seems completely normal, but in build.out I see
many linker warnings of the form

 > ld: warning: could not create compact unwind for _dchdc_: registers 72 and 73 
not saved contiguously in frame
 > ld: warning: could not create compact unwind for _dpoco_: registers 72 and 73 
not saved contiguously in frame
 > ld: warning: object file (/opt/R/arm64/lib/libreadline.a(history.o)) was 
built for newer macOS version (20.0) than being linked (11.0)
 > ld: warning: object file 
(/opt/R/arm64/lib/liblzma.a(liblzma_la-alone_decoder.o)) was built for newer 
macOS version (20.0) than being linked (11.0)

And the build eventually fails for a seemingly unrelated
reason:

 > clang -arch arm64 -dynamiclib -Wl,-headerpad_max_install_names -undefined 
dynamic_lookup -single_module -multiply_defined suppress -falign-functions=64 -g 
-O2 -Wall -pedantic -Wno-implicit-function-declaration -flto=thin -fPIC 
-Wl,-mllvm,-threads=4 -L/opt/homebrew/opt/zlib/lib -L/opt/R/arm64/lib 
-L/usr/local/lib -lomp -o tools.so text.o init.o Rmd5.o md5.o signals.o 
install.o getfmts.o http.o gramLatex.o gramRd.o pdscan.o -Wl,-framework 
-Wl,CoreFoundation
mkdir ../../../../library/tools/libs
 > installing 'sysdata.rda'
 > Error in dyn.load(file, DLLpath = DLLpath, ...) :
 >   unable to load shared object 
'/Users/mikael/Desktop/R/R-devel-build/library/tools/libs/tools.so':
 >   dlopen(/Users/mikael/Desktop/R/R-devel-build/library/tools/libs/tools.so, 
6): Symbol not found: _INTEGER
 >   Referenced from: 
/Users/mikael/Desktop/R/R-devel-build/library/tools/libs/tools.so
 >   Expected in: flat namespace
 >  in /Users/mikael/Desktop/R/R-devel-build/library/tools/libs/tools.so
 > Error: unable to load R code in package 'tools'
 > Execution halted

I've seen (and ignored) the "compact unwind" warnings before.
I've come across suggestions to append '-Wl,-no_compact_unwind'
to LDFLAGS, but it is not obvious to me that that is safe.

The warnings about macOS version mismatch are new, and strange,
given that 20 is my Darwin version and 11 is my macOS version.
I have tried all of

CC=clang
CC="clang -target arm64-apple-macos11"   [copied from an example in R-admin]
CC="clang -arch arm64"                   [copied from CRAN's Makeconf]

(and similarly for CXX) to no avail. I can trick the linker
with '-target arm64-apple-macos20' but that doesn't seem safe
either.

I'd be grateful for any hints on how to get things working,
again.

Mikael
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