wasm-ld: error: test.o: relocation R_WASM_MEMORY_ADDR_LEB cannot be used against symbol version_getter; recompile with -fPIC

[nomeata]

Bugzilla Link	43393
Version	12.0
OS	Linux

Extended Description

This used to work at revision 358327, but seems to have stopped working with the 9 release. Consider the file (test.c:

int get_version() { return 0; }
int (*version_getter)() = &get_version;
attribute ((visibility("default"))) int version() { return (*version_getter)(); }

Compiling this with

clang-9 --compile -fpic -fvisibility=hidden --target=wasm32-unknown-unknown-wasm -fno-builtin -ffreestanding test.c -o test.o
wasm-ld -o test.wasm --import-memory --shared --no-entry --gc-sections --export=__wasm_call_ctors test.o

yields

wasm-ld: error: test.o: relocation R_WASM_MEMORY_ADDR_LEB cannot be used against symbol version_getter; recompile with -fPIC

But note that I am compiling it with -fPIC (and it used to work).

[nomeata]

Mild ping, if that’s ok? It would at least be good to at least know if this should work, or if it is unsupported.

[nomeata]

Just checked with latest revision 375226, and the problem still exists.

[nomeata]

The problem seems to be with clang, not lld:

If I build with latest clang, but then try to link with wasm-ld from 358327 (the version that used to work), I still get that error.

If I build witht the old clang, I can link with the new wasm-ld, it works.

[nomeata]

Reading a bit through the git log, maybe https://reviews.llvm.org/D61539 by Sam Clegg might be related, or any of these;

git lg fc59a03..HEAD -G R_WASM_MEMORY_ADDR_LEB

• 9abe8c4 - [lld][WebAssembly] Report undefined symbols during scanRelocations (vor 3 Monaten)
• d0e1d00 - [lld][WebAssembly] Fix typo in error message (vor 4 Monaten)
• cadcb9e - [WebAssembly] Fix list of relocations with addends in lld (vor 4 Monaten)
• 8fcf012 - [WebAssembly] Refactor synthetic sections and relocation processing. NFC. (vor 5 Monaten)
• 0b13ca2 - [WebAssembly] Refactor relocation processing. NFC. (vor 5 Monaten)
• 08fa01a - Revert "[WebAssembly] Don't generate unused table entries." (vor 6 Monaten)
• b33fdb7 - [WebAssembly] Don't generate unused table entries. (vor 6 Monaten)
• 7cdec27 - [WebAssembly] Error on relocations against undefined data symbols. (vor 6 Monaten)

[nomeata]

Still present in 65f61c0
(there was some possibly related change in https://reviews.llvm.org/D69600 so I was optimistic)

[nomeata]

I did a git bisect (yay for moder tools), and found the commit that broke this for me:

commit 53572d0
Author: Dan Gohman dan433584@gmail.com
Date: Wed Jun 5 20:01:01 2019 +0000

[WebAssembly] Limit PIC support to the Emscripten target

The current PIC support currently only works with Emscripten, so
disable it for other targets.

This is the PIC portion of https://reviews.llvm.org/D62542.

Reviewed By: dschuff, sbc100

llvm-svn: 362638

[nomeata]

Ha, I guess I can just use --target=wasm32-unknown-emscripten-wasm instead of --target=wasm32-unknown-unknown-wasm and things works. Not sure what the implications of this are, but it seems to unblock me for now.

[nomeata]

Hmm, this worked for a while (llvm10, using --target=wasm32-emscripten), but after an upgrade of nixpkgs, it stopped working again.

Unfortunately, I am a bit out of my depth here.

[nomeata]

Hmm, maybe it stopped working when using wasi instead of emscripten in the target?

[km19809]

Is there any update? I'm suffering a similar issue.

[llvmbot]

@llvm/issue-subscribers-lld-wasm

[sbc100]

Simplified example:

$ cat test.c
int (*func_ptr)();

int version() {
  return func_ptr();
}
$ clang -c -fPIC -fvisibility=default --target=wasm32-unknown-emscripten test.c 
$ wasm-ld -o test.wasm --shared test.o 
wasm-ld: warning: creating shared libraries, with -shared, is not yet stable
wasm-ld: error: test.o: relocation R_WASM_MEMORY_ADDR_LEB cannot be used against symbol `func_ptr`; recompile with -fPIC

The problem only occurs when compiling with wasm32-unknown-unknown. With wasm32-unknown-emscripten it works as expected:

$ clang -c -fPIC -fvisibility=default --target=wasm32-unknown-emscripten test.c -o test.o
$ wasm-ld -o test.wasm --shared test.o
wasm-ld: warning: creating shared libraries, with -shared, is not yet stable

As the warnings say the PIC ABI is somewhat experimental and that only place it is know to actually work and get tested is within emscripten.

[sbc100]

I think this can be closed as expected behaviour, but can you first confirm that using the emscripten triple with ToT works for you?

[km19809]

@sbc100 I tested your emscripten triplet example, then It compiled successfully.
That means my problem does not come from this issue.
As I think, it can be closed now.
Thank you.