Why compiling with musl on Alpine fails and on ArchLinux succeeds - compilation

Question

This is a curiosity question: why?
Why does it have a different behavior for the exact same code?
I often have the issue that I can compile something in one distribution but not in another. So today I bumped into one of those issue again where when I build in the same way PostgreSQL's pg_dump with ArchLinux it works, but when I do it on Alpine it fails with this error:
gcc -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -Wno-format-truncation -Wno-stringop-truncation -static -fPIC -D_REENTRANT -D_THREAD_SAFE -D_POSIX_PTHREAD_SEMANTICS -fPIC -shared -Wl,-soname,libpq.so.5 -Wl,--version-script=exports.list -o libpq.so.5.11 fe-auth.o fe-auth-scram.o fe-connect.o fe-exec.o fe-misc.o fe-print.o fe-lobj.o fe-protocol2.o fe-protocol3.o pqexpbuffer.o fe-secure.o libpq-events.o chklocale.o inet_net_ntop.o noblock.o pgstrcasecmp.o pqsignal.o thread.o getpeereid.o pg_strong_random.o encnames.o wchar.o base64.o ip.o md5.o scram-common.o saslprep.o unicode_norm.o sha2.o -L../../../src/port -L../../../src/common -Wl,--as-needed -Wl,-rpath,'/usr/local/pgsql/lib',--enable-new-dtags
/lib/gcc/x86_64-linux-musl/8.2.0/../../../../x86_64-linux-musl/bin/ld: /lib/gcc/x86_64-linux-musl/8.2.0/crtbeginT.o: relocation R_X86_64_32 against hidden symbol `__TMC_END__' can not be used when making a shared object
/lib/gcc/x86_64-linux-musl/8.2.0/../../../../x86_64-linux-musl/bin/ld: /lib/gcc/x86_64-linux-musl/8.2.0/crtend.o: relocation R_X86_64_32 against `.ctors' can not be used when making a shared object; recompile with -fPIC
/lib/gcc/x86_64-linux-musl/8.2.0/../../../../x86_64-linux-musl/bin/ld: final link failed: nonrepresentable section on output
collect2: error: ld returned 1 exit status
make[1]: Leaving directory '/src/src/interfaces/libpq'
make[1]: *** [../../../src/Makefile.shlib:309: libpq.so.5.11] Error 1
make: *** [../../../src/Makefile.global:580: submake-libpq] Error 2
Here is the Dockerfile for Alpine:
FROM muslcc/x86_64:x86_64-linux-musl
RUN apk update && apk add make
ENV DOWNLOAD_URL https://ftp.postgresql.org/pub/source/v11.2/postgresql-11.2.tar.bz2
WORKDIR /src
RUN wget "$DOWNLOAD_URL" && \
tar xvjf "${DOWNLOAD_URL##*/}" --strip-components=1 && \
rm -fv "${DOWNLOAD_URL##*/}"
# NOTE: I left the -fPIC here for clarity sake but it fails with
# the same error with or without it
RUN ./configure --without-readline --without-zlib CFLAGS="-static -fPIC"
RUN cd src/bin/pg_dump && make pg_dump
Here is the Dockerfile for ArchLinux:
FROM archlinux/base
RUN pacman -Syu --noconfirm --needed base-devel musl
ENV DOWNLOAD_URL https://ftp.postgresql.org/pub/source/v11.2/postgresql-11.2.tar.bz2
WORKDIR /src
RUN curl -o "${DOWNLOAD_URL##*/}" "$DOWNLOAD_URL" && \
tar xvjf "${DOWNLOAD_URL##*/}" --strip-components=1 && \
rm -fv "${DOWNLOAD_URL##*/}"
RUN ./configure --without-readline --without-zlib CC="musl-gcc" CFLAGS="-static"
RUN cd src/bin/pg_dump && make pg_dump
I don't even know where to look at. Could it be a difference of version of musl? Another compiling tool? I don't really want the solution, I want to understand why.

Answer 1

I don't have that much experience with Alpine Linux and I would need to play with it myself, but it seems some pretty basic standard C libraries are built as non-platform-independent-code (PIC), which means you aren't allowed to link a dynamic library with it.
I'd start chasing Alpine Linux developers about this, because there are probably configuration flags for PostgreSQL which would allow you to build what you want.
Now, I've notices one thing. You pass CFLAGS=-static to the compilation, but it's pointless as ./configure already set it up as shared - look carefully at the compiler invocation you quote. If you want static build, you need to find a proper configuration flag and use it with ./configure. I your case --disable-shared should work.
CFLAGS="-static" CXXFLAGS="-static" LDFLAGS="-Wl,-Bstatic" ./configure --without-readline --without-zlib
seem to enable -static without leaving -shared.