Build lfi-static-bind:

meson setup build
cd build
ninja

Build sandbox/stub.elf and sandbox/host.so (requires mold):

$ make -C sandbox
clang -shared -fPIC host.c -O2 -o host.so -fuse-ld=mold -Wl,--spare-program-headers=7
x86_64-lfi-linux-musl-clang add.c stub.c -O2 -o stub.elf -static-pie

Dump info for stub and host:

$ readelf --segments sandbox/stub.elf
Program Headers:
  Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  PHDR           0x0000000000000040 0x0000000000000040 0x0000000000000040
                 0x00000000000001f8 0x00000000000001f8  R      0x8
  LOAD           0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x00000000000003d4 0x00000000000003d4  R      0x1000
  LOAD           0x0000000000001000 0x0000000000001000 0x0000000000001000
                 0x000000000000154d 0x000000000000154d  R E    0x1000
  LOAD           0x0000000000003000 0x0000000000003000 0x0000000000003000
                 0x0000000000000158 0x0000000000001000  RW     0x1000
  LOAD           0x0000000000003158 0x0000000000004158 0x0000000000004158
                 0x0000000000000010 0x0000000000000280  RW     0x1000
  DYNAMIC        0x0000000000003010 0x0000000000003010 0x0000000000003010
                 0x0000000000000120 0x0000000000000120  RW     0x8
  GNU_RELRO      0x0000000000003000 0x0000000000003000 0x0000000000003000
                 0x0000000000000158 0x0000000000001000  R      0x1
  GNU_EH_FRAME   0x0000000000000318 0x0000000000000318 0x0000000000000318
                 0x000000000000002c 0x000000000000002c  R      0x4
  GNU_STACK      0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x0000000000000000 0x0000000000000000  RW     0x0

$ readelf --segments sandbox/host.so
Program Headers:
  Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  PHDR           0x0000000000000040 0x0000000000000040 0x0000000000000040
                 0x00000000000003b8 0x00000000000003b8  R      0x8
  NOTE           0x00000000000003f8 0x00000000000003f8 0x00000000000003f8
                 0x0000000000000024 0x0000000000000024  R      0x4
  LOAD           0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x00000000000006a0 0x00000000000006a0  R      0x1000
  LOAD           0x00000000000006a0 0x00000000000016a0 0x00000000000016a0
                 0x0000000000000141 0x0000000000000141  R E    0x1000
  LOAD           0x00000000000007e8 0x00000000000027e8 0x00000000000027e8
                 0x00000000000001f8 0x0000000000000818  RW     0x1000
  LOAD           0x00000000000009e0 0x00000000000039e0 0x00000000000039e0
                 0x0000000000000028 0x0000000000000029  RW     0x1000
  DYNAMIC        0x00000000000007e8 0x00000000000027e8 0x00000000000027e8
                 0x00000000000001c0 0x00000000000001c0  RW     0x8
  GNU_EH_FRAME   0x0000000000000684 0x0000000000000684 0x0000000000000684
                 0x0000000000000014 0x0000000000000014  R      0x4
  GNU_STACK      0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x0000000000000000 0x0000000000000000  RW     0x1
  GNU_RELRO      0x00000000000007e8 0x00000000000027e8 0x00000000000027e8
                 0x00000000000001f8 0x0000000000000818  R      0x1
  NULL           0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x0000000000000000 0x0000000000000000         0x0
  NULL           0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x0000000000000000 0x0000000000000000         0x0
  NULL           0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x0000000000000000 0x0000000000000000         0x0
  NULL           0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x0000000000000000 0x0000000000000000         0x0
  NULL           0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x0000000000000000 0x0000000000000000         0x0
  NULL           0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x0000000000000000 0x0000000000000000         0x0
  NULL           0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x0000000000000000 0x0000000000000000         0x0

Build host_combined.so:

./build/lfi-static-bind sandbox/stub.elf sandbox/host.so -o host_combined.so

Dump info for host_combined.so:

$ readelf --segments host_combined.so
Program Headers:
  Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  PHDR           0x0000000000000040 0x0000000000000040 0x0000000000000040
                 0x00000000000003b8 0x00000000000003b8  R      0x8
  NOTE           0x00000000000003f8 0x00000000000003f8 0x00000000000003f8
                 0x0000000000000024 0x0000000000000024  R      0x4
  LOAD           0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x00000000000006a0 0x00000000000006a0  R      0x1000
  LOAD           0x00000000000006a0 0x00000000000016a0 0x00000000000016a0
                 0x0000000000000141 0x0000000000000141  R E    0x1000
  LOAD           0x00000000000007e8 0x00000000000027e8 0x00000000000027e8
                 0x00000000000001f8 0x0000000000000818  RW     0x1000
  LOAD           0x00000000000009e0 0x00000000000039e0 0x00000000000039e0
                 0x0000000000000028 0x0000000000000029  RW     0x1000
  DYNAMIC        0x00000000000007e8 0x00000000000027e8 0x00000000000027e8
                 0x00000000000001c0 0x00000000000001c0  RW     0x8
  GNU_EH_FRAME   0x0000000000000684 0x0000000000000684 0x0000000000000684
                 0x0000000000000014 0x0000000000000014  R      0x4
  GNU_STACK      0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x0000000000000000 0x0000000000000000  RW     0x1
  GNU_RELRO      0x00000000000007e8 0x00000000000027e8 0x00000000000027e8
                 0x00000000000001f8 0x0000000000000818  R      0x1
  LOAD           0x0000000000000000 0x0000000000004000 0x0000000000004000
                 0x0000000000000000 0x0000000000014000         0x1000
  LOAD           0x0000000000000000 0x0000000000018000 0x0000000000018000
                 0x0000000000000000 0x0000000000001000  RW     0x1000
  LOAD           0x0000000000002000 0x0000000000019000 0x00000000000003f8
                 0x00000000000003d4 0x00000000000003d4  R      0x1000
  LOAD           0x0000000000003000 0x000000000001a000 0x0000000000000000
                 0x000000000000154d 0x000000000000154d  R E    0x1000
  LOAD           0x0000000000005000 0x000000000001c000 0x00000000000016a0
                 0x0000000000000158 0x0000000000001000  RW     0x1000
  LOAD           0x0000000000005158 0x000000000001d158 0x00000000000027e8
                 0x0000000000000010 0x0000000000000280  RW     0x1000
  LOAD           0x0000000000000000 0x000000000001e000 0x000000000001e000
                 0x0000000000000000 0x000000010000f000         0x1000