Build with static libzstd (was: Re: GDB: How does configure with with config.cache??)

On Wed, 2024-09-11 at 18:10 -0400, Paul Smith via Gdb wrote:
> Can someone explain to me how the GDB top-level configure script
> works?  It's driving me bananas.

OK, as might be expected most of this was my fault and my
misunderstanding: my build tool accidentally was not deleting a
previous build directory.  After I got some sleep last night the
gremlins I was fighting all left town.

The thing that is wrong now is that I build libzstd as a static library
with multithreaded support, and I want to link it statically but this
doesn't work well.

I am configuring GDB with --enable-static --disable-shared (but this is
probably related to GDB itself not its prerequisites).

The problem is that when the GDB configure uses pkg-config to get
details about the libzstd package, it doesn't pass the --static option
and so the resulting link options don't contain -pthread:

  $ pkg-config --libs libzstd
  -L/data/src/zstd/Linux-Release-make/dist/lib -lzstd

  $ pkg-config --libs --static libzstd
  -L/data/src/zstd/Linux-Release-make/dist/lib -lzstd -pthread

Because -pthread is missing in the first case, the configure test
programs that try to link code fail; for example:

  configure:27555: checking for ELF support in BFD
  configure:27575: ./libtool --quiet --mode=link x86_64-rl84-linux-gnu-gcc -o conftest -I/data/src/gdb/gdb-15.1/gdb/../include -I../bfd -I/data/src/gdb/gdb-15.1/gdb/../bfd -O2 -fPIC -static-libgcc     -I/data/src/xxhash/Linux-Release-make/dist/include -L../bfd -L../libiberty   conftest.c -lbfd -liberty  -lncurses -lm -ldl  >&5
  /data/src/zstd/Linux-Release-make/dist/lib/libzstd.a(pool.c.o):pool.c:function POOL_free:(.text+0x15f): error: undefined reference to 'pthread_join'
  /data/src/zstd/Linux-Release-make/dist/lib/libzstd.a(pool.c.o):pool.c:function POOL_create_advanced:(.text+0x3a9): error: undefined reference to 'pthread_create'
  /data/src/zstd/Linux-Release-make/dist/lib/libzstd.a(pool.c.o):pool.c:function POOL_resize:(.text+0x689): error: undefined reference to 'pthread_create'
  collect2: error: ld returned 1 exit status
  configure:27585: result: no

This is obviously problematic since gcore-elf.c is not included in GDB
and the build fails.


I'm not really sure what the right answer is here.  I could of course
force -pthread always by adding LIBS=-pthread to the configure command.

Or maybe the problem is that the libzstd.pc file is wrong: since I
don't have a libzstd.so but only libzstd.a maybe the pc file should
include -pthread in the Libs variable and not just in the Libs.private
variable?

I'll move forward with some kind of workaround, locally.