lld: pointer remains blank in custom section

[erenon]

My application stores a pointer to a string in a custom ELF section. LLD leaves the pointer 0, while other linkers set it correctly.
Minimal repro:

#include <cstdint>
#include <cstdio>

int main() {

  __attribute__((section(".custom"), used, retain))
  static constexpr const char* x[] = {
    __FILE__
  };
  const std::uint64_t id = std::uint64_t(&x);
  printf("%lu\n", id);
}

combined with:

app: app.cpp
	$(CXX) $< -o $@ -fuse-ld=$(LD)

test: app
	readelf -x .custom $<

Test cases:

$ CXX=$(which clang++) LD=bfd make test -B    # ok
$ CXX=$(which clang++) LD=gold make test -B  # ok
$ CXX=$(which clang++) LD=lld make test -B     # BROKEN
$ CXX=$(which g++) LD=bfd make test -B    # ok
$ CXX=$(which g++) LD=gold make test -B  # ok
$ CXX=$(which g++) LD=lld make test -B     # BROKEN

Example good output:

$ readelf -x .custom app

Hex dump of section '.custom':
  0x00002020 44070000 00000000                   D.......

Example bad output:

$ readelf -x .custom app

Hex dump of section '.custom':
  0x000039e8 00000000 00000000                   ........

Versions:

$ clang++ -v
Ubuntu clang version 14.0.0-1ubuntu1
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/11
Selected GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/11
Candidate multilib: .;@m64
Selected multilib: .;@m64

$ ld.lld -v
Ubuntu LLD 14.0.0 (compatible with GNU linkers)

[llvmbot]

@llvm/issue-subscribers-lld-elf

[MaskRay]

ld.lld's behavior is different from GNU ld and gold, but the behavior is still correct (it improves text section compressing).
.custom has a dynamic relocation. After rtld applies the relocation, the location in .custom will point to the string literal. See https://maskray.me/blog/2020-12-19-lld-and-gnu-linker-incompatibilities --apply-dynamic-relocs