Compiling mpfr 4.0.2 on AIX fails to configure TLS support - aix

Question

I'm trying to compile mpfr on AIX and get an error finding TLS support. My end goal is to have a working gcc (9.3) with libstdc++ support for threads and TLS.
I tried compiling with both an existing gcc on the machine (which is 8.3 and doesn't have TLS support, as it seems) and using the built-in xlC (V12.1) on the machine.
I compiled GMP-6.2.0:
(gcc attempt): ./configure --enable-shared --enable-static CFLAGS=-fPIC CXXFLAGS=-fPIC --prefix=$OUTDIR --host=powerpc-ibm-aix7.1.0.0
(xlc attempt): ./configure --enable-shared --enable-static CC=xlc CXX=xlc CFLAGS=-qPIC CXXFLAGS=-qPIC --prefix=$OUTDIR --host=powerpc-ibm-aix7.1.0.0
gmake all
gmake check
gmake install
In both cases gmp successfully tests and installs.
Trying to configure mpfr-4.0.2 results in
(gcc attempt): ./configure --enable-shared --enable-static CFLAGS=-fPIC CXXFLAGS=-fPIC --with-gmp=$OUTDIR --prefix=$OUTDIR --host=powerpc-ibm-aix7.1.0.0
(xlc attempt): ./configure --enable-shared --enable-static CC=xlc CXX=xlc CFLAGS="-qPIC -qtls" CXXFLAGS="-qPIC -qtls" --with-gmp=$OUTDIR --prefix=$OUTDIR --host=powerpc-ibm-aix7.1.0.0
results in the following error in config.log
(gcc attempt):
configure:16567: checking for TLS support
configure:16595: gcc -o conftest -fPIC -I{OUTDIR}/include -I./src -L{OUTDIR}/lib conftest.c >&5
ld: 0711-317 ERROR: Undefined symbol: __tls_get_addr
(xlc attempt):
configure:16567: checking for TLS support
configure:16595: xlc -o conftest -qPIC -qtls -I{OUTDIR}/include -I./src -L{OUTDIR}/lib conftest.c >&5
ld: 0711-317 ERROR: Undefined symbol: .__tls_get_addr
I've tried a dozen different flags and configurations but mostly I don't think I'm in the correct direction - every dependency seems circular. I believe compiling with xlc is the correct idea here, but I just can't figure how to get it properly support TLS.
I also thought that I can ignore this and continue, and later compile libstdc++ again with support for TLS - but that also brought me to a dead end.
Edit:
Taking more actions on using xlc: I tried compiling the generated conftest.c (https://gist.github.com/NitzanEgozy/265e54e3353aefc79558c860b543a98f) manually:
$ xlc -o conftest -qPIC -qtls -I$OUTDIR/include -I./src -L$OUTDIR/lib conftest.c -bnoquiet
(ld): halt 4
(ld): setfflag 4
(ld): savename conftest
(ld): filelist 6 1
(ld): i /lib/crt0.o
(ld): i conftest.o
(ld): lib /usr/vac/lib/libxlopt.a
(ld): lib /usr/vac/lib/libxlipa.a
(ld): lib /usr/vac/lib/libxl.a
(ld): lib /usr/lib/libc.a
LIBRARY: Shared object libc.a[shr.o]: 3301 symbols imported.
LIBRARY: Shared object libc.a[meth.o]: 2 symbols imported.
LIBRARY: Shared object libc.a[posix_aio.o]: 20 symbols imported.
LIBRARY: Shared object libc.a[aio.o]: 18 symbols imported.
LIBRARY: Shared object libc.a[pse.o]: 8 symbols imported.
LIBRARY: Shared object libc.a[dl.o]: 4 symbols imported.
LIBRARY: Shared object libc.a[pty.o]: 1 symbols imported.
LIBRARY: Shared object libc.a[cthread.o]: 25 symbols imported.
FILELIST: Number of previously inserted files processed: 6
(ld): resolve
RESOLVE: 33 of 7029 symbols were kept.
(ld): addgl /usr/lib/glink.o
ADDGL: Glink code added for 2 symbols.
(ld): er full
ld: 0711-318 ERROR: Undefined symbols were found.
The following symbols are in error:
Symbol Inpndx TY CL Source-File(Object-File) OR Import-File{Shared-object}
RLD: Address Section Rld-type Referencing Symbol
----------------------------------------------------------------------------------------------
.__tls_get_addr [30] ER PR conftest.c(conftest.o)
00000010 .text R_RBA [16] .main
Removing -qtls throws The '__thread' keyword is not supported on the target platform. The keyword is ignored.

Answer 1

AFAIK if native TLS is not available gcc emulates it using pthread keys, and i think gcc does not even support native TLS on aix. adding "-pthread" flag to the configuration will enable the appropriate threading support.
the current gcc from the ibm aixtoolbox has the appropriate default threading model enabled, hope this helps a little bit.
root#aixbuildhostng: /root # gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/opt/freeware/libexec/gcc/powerpc-ibm-aix7.1.0.0/8.3.0/lto-wrapper
Target: powerpc-ibm-aix7.1.0.0
Configured with: ../gcc-8.3.0/configure --prefix=/opt/freeware --mandir=/opt/freeware/man --infodir=/opt/freeware/info --with-local-prefix=/opt/freeware --with-as=/usr/bin/as --with-ld=/usr/bin/ld --enable-languages=c,c++,fortran,objc,obj-c++ --enable-version-specific-runtime-libs --disable-nls --enable-decimal-float=dpd --with-cloog=no --with-ppl=no --disable-libstdcxx-pch --enable-__cxa_atexit --host=powerpc-ibm-aix7.1.0.0
Thread model: aix
gcc version 8.3.0 (GCC)
mpfr 4.0.2 is also available as an rpm package:
root#aixbuildhostng: /root # yum search mpfr
Loaded plugins: aliases, allowdowngrade, basearchonly, changelog, downloadonly, fastestmirror, filter-data, keys, list-data, local, merge-conf, post-transaction-actions, priorities, protectbase, ps, remove-with-leaves, rpm-warm-cache,
: show-leaves, tmprepo, tsflags, verify, versionlock
Loading mirror speeds from cached hostfile
0 packages excluded due to repository protections
============================================================================================================= N/S Matched: mpfr =============================================================================================================
mpfr-devel.ppc : Development tools A C library for mpfr library
mpfr.ppc : A C library for multiple-precision floating-point computations
ad bootstrapping gcc via xlc...this quite a sophisticated task, i never managed to make this work.
https://gcc.gnu.org/install/specific.html#x-ibm-aix