branch: master
commit 9ea17fa02dc91b981a1ef0a29f1d7e597b622afa
Author: Alexandre Janniaux <[email protected]>
AuthorDate: Tue Mar 10 18:46:58 2026 +0100
m4/libtool.m4: fix emscripten CXX postdeps using non-PIC sysroot
Commit d8a934458b251b465b7d31da9ba9148a128a146d introduced shared
libraries support for emscripten, using -sSIDE_MODULE=1, but the CXX
dependency detection in _LT_SYS_HIDDEN_LIBDEPS will only try to use
`-shared` link option to discover implicit dependencies.
The libraries and search paths reported by em++ differ depending on
whether -sSIDE_MODULE=2 is passed:
em++ -shared -v conftest.o:
-L<sysroot>/lib/wasm32-emscripten (<-- non-PIC)
-lhtml5... (other -l flags)
em++ -sSIDE_MODULE=2 -shared -v conftest.o
-L<sysroot>/lib/wasm32-emscripten/pic (<-- PIC)
(no -l flags)
Without -sSIDE_MODULE=2, the detected postdeps contain the non-PIC
sysroot path and system libraries. These get injected into the CXX
shared library link line before emcc can append the PIC sysroot,
causing wasm-ld to resolve system libraries from non-PIC archives,
typically in VLC build system:
error: R_WASM_MEMORY_ADDR_LEB cannot be used against symbol;
recompile with -fPIC
We resolved the issue in VLC by patching the postdeps but they were not
generated properly in the first place.
Fix by overriding output_verbose_link_cmd for emscripten in
_LT_LANG_CXX_CONFIG. The override passes -sSIDE_MODULE=2, matching what
archive_cmds actually uses at link time so that the detected paths point
to the PIC sysroot.
* NEWS: Update.
---
NEWS | 2 ++
m4/libtool.m4 | 8 ++++++++
2 files changed, 10 insertions(+)
diff --git a/NEWS b/NEWS
index 091b99b6..813eb1a4 100644
--- a/NEWS
+++ b/NEWS
@@ -30,6 +30,8 @@ NEWS - list of user-visible changes between releases of GNU
Libtool
- Recognise more static linking options for Clang.
+ - Fix emscripten CXX postdeps using non-PIC sysroot.
+
** Changes in supported systems or compilers:
- Add support for SlimCC compiler.
diff --git a/m4/libtool.m4 b/m4/libtool.m4
index d8627ba2..84a34a12 100644
--- a/m4/libtool.m4
+++ b/m4/libtool.m4
@@ -7704,6 +7704,14 @@ if test yes != "$_lt_caught_CXX_error"; then
_LT_TAGVAR(ld_shlibs, $1)=no
;;
+ emscripten*)
+ # Emscripten side modules (-sSIDE_MODULE=2) use a separate PIC sysroot
+ # and do not link system libraries (they are imported from the main
module
+ # at runtime). Re-run the verbose link with -sSIDE_MODULE=2 so that
the
+ # detected paths point to the PIC sysroot instead of the non-PIC one.
+ output_verbose_link_cmd='$CC -sSIDE_MODULE=2 -shared $CFLAGS -v
conftest.$objext 2>&1 | $GREP " [[-]]L"'
+ ;;
+
*)
# FIXME: insert proper C++ library support
_LT_TAGVAR(ld_shlibs, $1)=no
