bpo-40280: Add --enable-wasm-dynamic-linking (GH-32253)

6 files changed, 194 insertions, 49 deletions

diff --git a/Doc/using/configure.rst b/Doc/using/configure.rst
index debbee7..b46157c 100644
--- a/Doc/using/configure.rst
+++ b/Doc/using/configure.rst
@@ -52,11 +52,13 @@ General Options
    Set the Python executable suffix to *SUFFIX*.
 
    The default suffix is ``.exe`` on Windows and macOS (``python.exe``
-   executable), ``.wasm`` on Emscripten (``python.wasm`` executable), and
-   an empty string on other platforms (``python`` executable).
+   executable), ``.js`` on Emscripten node, ``.html`` on Emscripten browser,
+   ``.wasm`` on WASI, and an empty string on other platforms (``python``
+   executable).
 
    .. versionchanged:: 3.11
-      The default suffix on Emscripten platform is ``.wasm``.
+      The default suffix on WASM platform is one of ``.js``, ``.html``
+      or ``.wasm``.
 
 .. cmdoption:: --with-tzpath=<list of absolute paths separated by pathsep>
 
@@ -141,6 +143,27 @@ General Options
 
    .. versionadded:: 3.11
 
+WebAssemby Options
+------------------
+
+.. cmdoption:: --with-emscripten-target=[browser|node]
+
+   Set build flavor for ``wasm32-emscripten``.
+
+   * ``browser`` (default): preload minimal stdlib, default MEMFS.
+   * ``node``: NODERAWFS and pthread support.
+
+   .. versionadded:: 3.11
+
+.. cmdoption:: --enable-wasm-dynamic-linking
+
+   Turn on dynamic linking support for WASM.
+
+   Dynamic linking enables ``dlopen``. File size of the executable
+   increases due to limited dead code elimination and additional features.
+
+   .. versionadded:: 3.11
+
 
 Install Options
 ---------------
diff --git a/Misc/NEWS.d/next/Build/2022-04-02-17-52-38.bpo-40280.U8Dd0H.rst b/Misc/NEWS.d/next/Build/2022-04-02-17-52-38.bpo-40280.U8Dd0H.rst
new file mode 100644
index 0000000..74fe5c7
--- /dev/null
+++ b/Misc/NEWS.d/next/Build/2022-04-02-17-52-38.bpo-40280.U8Dd0H.rst
@@ -0,0 +1,2 @@
+Add configure option :option:`--enable-wasm-dynamic-linking` to enable
+``dlopen`` and MAIN_MODULE / SIDE_MODULE on ``wasm32-emscripten``.
diff --git a/Tools/wasm/README.md b/Tools/wasm/README.md
index 1cdaa4e..6b1e7b0 100644
--- a/Tools/wasm/README.md
+++ b/Tools/wasm/README.md
@@ -81,24 +81,31 @@ node --experimental-wasm-threads --experimental-wasm-bulk-memory builddir/emscri
 
 ## wasm32-emscripten limitations and issues
 
+- Heap and stack are limited.
 - Most stdlib modules with a dependency on external libraries are missing:
   ``ctypes``, ``readline``, ``sqlite3``, ``ssl``, and more.
 - Shared extension modules are not implemented yet. All extension modules
   are statically linked into the main binary.
+  The experimental configure option ``--enable-wasm-dynamic-linking`` enables
+  dynamic extensions.
 - Processes are not supported. System calls like fork, popen, and subprocess
   fail with ``ENOSYS`` or ``ENOSUP``.
+- Only ``AF_INET`` and ``AF_INET6`` with ``SOCK_STREAM`` (TCP) or
+  ``SOCK_DGRAM`` (UDP) are available. ``AF_UNIX`` is not supported.
+- ``socketpair`` does not work.
 - Blocking sockets are not available and non-blocking sockets don't work
   correctly, e.g. ``socket.accept`` crashes the runtime. ``gethostbyname``
   does not resolve to a real IP address. IPv6 is not available.
 - The ``select`` module is limited. ``select.select()`` crashes the runtime
   due to lack of exectfd support.
-- The ``*at`` variants of functions (e.g. ``openat``) are not available.
-  The ``dir_fd`` argument of *os* module functions can't be used.
 - Signal support is limited. ``signal.alarm``, ``itimer``, ``sigaction``
   are not available or do not work correctly. ``SIGTERM`` exits the runtime.
 - Most user, group, and permission related function and modules are not
   supported or don't work as expected, e.g.``pwd`` module, ``grp`` module,
-  ``os.setgroups``, ``os.chown``, and so on.
+  ``os.setgroups``, ``os.chown``, and so on. ``lchown`` and `lchmod`` are
+  not available.
+- ``umask`` is a no-op.
+- hard links (``os.link``) are not supported.
 - Offset and iovec I/O functions (e.g. ``os.pread``, ``os.preadv``) are not
   available.
 - ``os.mknod`` and ``os.mkfifo``
@@ -108,17 +115,9 @@ node --experimental-wasm-threads --experimental-wasm-bulk-memory builddir/emscri
 - ``mmap`` module is unstable. flush (``msync``) can crash the runtime.
 - Resource-related functions like ``os.nice`` and most functions of the
   ``resource`` module are not available.
-- Some time and datetime features are broken. ``strftime`` and ``strptime``
-  have known bugs, e.g.
-  [%% quoting](https://github.com/emscripten-core/emscripten/issues/16155),
-  [%U off-by-one](https://github.com/emscripten-core/emscripten/issues/16156).
-  Extended glibc formatting features are not available.
+- glibc extensions for date and time formatting are not available.
 - ``locales`` module is affected by musl libc issues,
   [bpo-46390](https://bugs.python.org/issue46390).
-- ``uuid`` module is affected by
-  [memory leak](https://github.com/emscripten-core/emscripten/issues/16081)
-  and crasher in Emscripten's ``freeaddrinfo``,
-- Recursive ``glob`` leaks file descriptors.
 - Python's object allocator ``obmalloc`` is disabled by default.
 - ``ensurepip`` is not available.
 
diff --git a/Tools/wasm/config.site-wasm32-emscripten b/Tools/wasm/config.site-wasm32-emscripten
index 60ede49..3363664 100644
--- a/Tools/wasm/config.site-wasm32-emscripten
+++ b/Tools/wasm/config.site-wasm32-emscripten
@@ -91,7 +91,3 @@ ac_cv_func_linkat=no
 
 # alarm signal is not delivered, may need a callback into the event loop?
 ac_cv_func_alarm=no
-
-# To use dlopen, you need to use Emscripten's linking support,
-# see https://emscripten.org/docs/compiling/Dynamic-Linking.html
-ac_cv_func_dlopen=no
diff --git a/configure b/configure
index a06d4c9..72d8880 100755
--- a/configure
+++ b/configure
@@ -1017,6 +1017,7 @@ with_framework_name
 enable_framework
 with_cxx_main
 with_emscripten_target
+enable_wasm_dynamic_linking
 with_suffix
 enable_shared
 with_static_libpython
@@ -1730,6 +1731,9 @@ Optional Features:
                           Unix install. optional INSTALLDIR specifies the
                           installation path. see Mac/README.rst (default is
                           no)
+  --enable-wasm-dynamic-linking
+                          Enable dynamic linking support for WebAssembly
+                          (default is no)
   --enable-shared         enable building a shared Python library (default is
                           no)
   --enable-profiling      enable C-level code profiling with gprof (default is
@@ -6290,6 +6294,30 @@ fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_sys_emscripten_target" >&5
 $as_echo "$ac_sys_emscripten_target" >&6; }
 
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for --enable-wasm-dynamic-linking" >&5
+$as_echo_n "checking for --enable-wasm-dynamic-linking... " >&6; }
+# Check whether --enable-wasm-dynamic-linking was given.
+if test "${enable_wasm_dynamic_linking+set}" = set; then :
+  enableval=$enable_wasm_dynamic_linking;
+  case $ac_sys_system in #(
+  Emscripten) :
+     ;; #(
+  WASI) :
+    as_fn_error $? "WASI dynamic linking is not implemented yet." "$LINENO" 5 ;; #(
+  *) :
+    as_fn_error $? "--enable-wasm-dynamic-linking only applies to Emscripten and WASI" "$LINENO" 5
+   ;;
+esac
+
+else
+
+  enable_wasm_dynamic_linking=missing
+
+fi
+
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $enable_wasm_dynamic_linking" >&5
+$as_echo "$enable_wasm_dynamic_linking" >&6; }
+
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for --with-suffix" >&5
 $as_echo_n "checking for --with-suffix... " >&6; }
 
@@ -7760,18 +7788,20 @@ then
 fi
 
 # WASM flags
-# TODO: Add -s MAIN_MODULE=2 for dlopen() support.
-# The option disables code elimination, which increases code size of main
-# binary. All objects must be built with -fPIC.
 case $ac_sys_system/$ac_sys_emscripten_target in #(
   Emscripten/browser*) :
 
-    LDFLAGS_NODIST="$LDFLAGS_NODIST -s ALLOW_MEMORY_GROWTH=1"
-    LINKFORSHARED="--preload-file \$(WASM_ASSETS_DIR)"
+    LDFLAGS_NODIST="$LDFLAGS_NODIST -sALLOW_MEMORY_GROWTH=1"
+    LINKFORSHARED="--preload-file=\$(WASM_ASSETS_DIR)"
+    if test "x$enable_wasm_dynamic_linking" = xyes; then :
+
+      as_fn_append LINKFORSHARED " -sMAIN_MODULE=1"
+
+fi
     WASM_ASSETS_DIR=".\$(prefix)"
     WASM_STDLIB="\$(WASM_ASSETS_DIR)/local/lib/python\$(VERSION)/os.py"
         if test "$Py_DEBUG" = 'true' -o "$ac_sys_emscripten_target" = "browser-debug"; then
-      LDFLAGS_NODIST="$LDFLAGS_NODIST -s ASSERTIONS=1"
+      LDFLAGS_NODIST="$LDFLAGS_NODIST -sASSERTIONS=1"
       LINKFORSHARED="$LINKFORSHARED -gsource-map --emit-symbol-map"
     else
       LINKFORSHARED="$LINKFORSHARED -O2 -g0"
@@ -7779,11 +7809,16 @@ case $ac_sys_system/$ac_sys_emscripten_target in #(
    ;; #(
   Emscripten/node*) :
 
-    LDFLAGS_NODIST="$LDFLAGS_NODIST -s ALLOW_MEMORY_GROWTH=1 -s NODERAWFS=1 -s USE_PTHREADS=1"
-    LINKFORSHARED="-s PROXY_TO_PTHREAD=1 -s EXIT_RUNTIME=1"
+    LDFLAGS_NODIST="$LDFLAGS_NODIST -sALLOW_MEMORY_GROWTH=1 -sNODERAWFS=1 -sUSE_PTHREADS=1"
+    LINKFORSHARED="-sPROXY_TO_PTHREAD=1 -sEXIT_RUNTIME=1"
+    if test "x$enable_wasm_dynamic_linking" = xyes; then :
+
+      as_fn_append LINKFORSHARED " -sMAIN_MODULE=1"
+
+fi
     CFLAGS_NODIST="$CFLAGS_NODIST -pthread"
     if test "$Py_DEBUG" = 'true' -o "$ac_sys_emscripten_target" = "node-debug"; then
-      LDFLAGS_NODIST="$LDFLAGS_NODIST -s ASSERTIONS=1"
+      LDFLAGS_NODIST="$LDFLAGS_NODIST -sASSERTIONS=1"
       LINKFORSHARED="$LINKFORSHARED -gseparate-dwarf --emit-symbol-map"
     else
       LINKFORSHARED="$LINKFORSHARED -O2 -g0"
@@ -7808,6 +7843,18 @@ $as_echo "#define _WASI_EMULATED_PROCESS_CLOCKS 1" >>confdefs.h
      ;;
 esac
 
+case $enable_wasm_dynamic_linking in #(
+  yes) :
+    ac_cv_func_dlopen=yes ;; #(
+  no) :
+    ac_cv_func_dlopen=no ;; #(
+  missing) :
+
+ ;; #(
+  *) :
+     ;;
+esac
+
 
 
 
@@ -10469,10 +10516,6 @@ then
 	Linux*|GNU*|QNX*|VxWorks*|Haiku*)
 		LDSHARED='$(CC) -shared'
 		LDCXXSHARED='$(CXX) -shared';;
-	Emscripten*)
-		LDSHARED='$(CC) -shared -s SIDE_MODULE=1'
-		LDCXXSHARED='$(CXX) -shared -s SIDE_MODULE=1'
-    ;;
 	FreeBSD*)
 		if [ "`$CC -dM -E - </dev/null | grep __ELF__`" != "" ]
 		then
@@ -10511,16 +10554,32 @@ then
 	SCO_SV*)
 		LDSHARED='$(CC) -Wl,-G,-Bexport'
 		LDCXXSHARED='$(CXX) -Wl,-G,-Bexport';;
+	WASI*)
+		if test "x$enable_wasm_dynamic_linking" = xyes; then :
+
+
+fi;;
 	CYGWIN*)
 		LDSHARED="gcc -shared -Wl,--enable-auto-image-base"
 		LDCXXSHARED="g++ -shared -Wl,--enable-auto-image-base";;
 	*)	LDSHARED="ld";;
 	esac
 fi
+
+if test "$enable_wasm_dynamic_linking" = "yes" -a "$ac_sys_system" = "Emscripten"; then
+  BLDSHARED='$(CC) -shared -sSIDE_MODULE=1 -sWASM=1'
+fi
+
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $LDSHARED" >&5
 $as_echo "$LDSHARED" >&6; }
 LDCXXSHARED=${LDCXXSHARED-$LDSHARED}
+
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking BLDSHARED flags" >&5
+$as_echo_n "checking BLDSHARED flags... " >&6; }
 BLDSHARED=${BLDSHARED-$LDSHARED}
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $BLDSHARED" >&5
+$as_echo "$BLDSHARED" >&6; }
+
 # CCSHARED are the C *flags* used to create objects to go into a shared
 # library (module) -- this is only needed for a few systems
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking CCSHARED" >&5
@@ -10540,6 +10599,12 @@ then
 		 fi;;
 	Linux-android*) ;;
 	Linux*|GNU*) CCSHARED="-fPIC";;
+	Emscripten*|WASI*)
+		if test "x$enable_wasm_dynamic_linking" = xyes; then :
+
+			CCSHARED="-fPIC"
+
+fi;;
 	FreeBSD*|NetBSD*|OpenBSD*|DragonFly*) CCSHARED="-fPIC";;
 	Haiku*) CCSHARED="-fPIC";;
 	OpenUNIX*|UnixWare*)
@@ -10647,6 +10712,13 @@ then
 		CFLAGSFORSHARED='$(CCSHARED)'
 	esac
 fi
+
+if test "x$enable_wasm_dynamic_linking" = xyes; then :
+
+  CFLAGSFORSHARED='$(CCSHARED)'
+
+fi
+
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $CFLAGSFORSHARED" >&5
 $as_echo "$CFLAGSFORSHARED" >&6; }
 
@@ -15379,7 +15451,8 @@ $as_echo "yes" >&6; }
 fi
 
 if test "$have_zlib" = "yes" -a "$ac_sys_system" = "Emscripten" -a "$ZLIB_LIBS" = "-lz"; then
-  ZLIB_LIBS="-s USE_ZLIB=1"
+  ZLIB_CFLAGS="-sUSE_ZLIB=1"
+  ZLIB_LIBS="-sUSE_ZLIB=1"
 fi
 
 if test "x$have_zlib" = xyes; then :
@@ -15612,7 +15685,8 @@ $as_echo "yes" >&6; }
 fi
 
 if test "$have_bzip2" = "yes" -a "$ac_sys_system" = "Emscripten" -a "$BZIP2_LIBS" = "-lbz2"; then
-  BZIP2_LIBS="-s USE_BZIP2=1"
+  BZIP2_CFLAGS="-sUSE_BZIP2=1"
+  BZIP2_LIBS="-sUSE_BZIP2=1"
 fi
 
 
diff --git a/configure.ac b/configure.ac
index abcd379..fda2312 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1107,6 +1107,25 @@ dnl are free to remove them in the future.
 ])
 AC_MSG_RESULT([$ac_sys_emscripten_target])
 
+dnl On Emscripten dlopen() requires -s MAIN_MODULE and -fPIC. The flags
+dnl disables dead code elimination and increases the size of the WASM module
+dnl by about 1.5 to 2MB. MAIN_MODULE defines __wasm_mutable_globals__.
+dnl See https://emscripten.org/docs/compiling/Dynamic-Linking.html
+AC_MSG_CHECKING([for --enable-wasm-dynamic-linking])
+AC_ARG_ENABLE([wasm-dynamic-linking],
+  [AS_HELP_STRING([--enable-wasm-dynamic-linking],
+                  [Enable dynamic linking support for WebAssembly (default is no)])],
+[
+  AS_CASE([$ac_sys_system],
+    [Emscripten], [],
+    [WASI], [AC_MSG_ERROR([WASI dynamic linking is not implemented yet.])],
+    [AC_MSG_ERROR([--enable-wasm-dynamic-linking only applies to Emscripten and WASI])]
+  )
+], [
+  enable_wasm_dynamic_linking=missing
+])
+AC_MSG_RESULT([$enable_wasm_dynamic_linking])
+
 AC_MSG_CHECKING([for --with-suffix])
 AC_ARG_WITH([suffix],
             [AS_HELP_STRING([--with-suffix=SUFFIX], [set executable suffix to SUFFIX (default is empty, yes is mapped to '.exe')])],
@@ -1890,29 +1909,32 @@ then
 fi
 
 # WASM flags
-# TODO: Add -s MAIN_MODULE=2 for dlopen() support.
-# The option disables code elimination, which increases code size of main
-# binary. All objects must be built with -fPIC.
 AS_CASE([$ac_sys_system/$ac_sys_emscripten_target],
   [Emscripten/browser*], [
-    LDFLAGS_NODIST="$LDFLAGS_NODIST -s ALLOW_MEMORY_GROWTH=1"
-    LINKFORSHARED="--preload-file \$(WASM_ASSETS_DIR)"
+    LDFLAGS_NODIST="$LDFLAGS_NODIST -sALLOW_MEMORY_GROWTH=1"
+    LINKFORSHARED="--preload-file=\$(WASM_ASSETS_DIR)"
+    AS_VAR_IF([enable_wasm_dynamic_linking], [yes], [
+      AS_VAR_APPEND([LINKFORSHARED], [" -sMAIN_MODULE=1"])
+    ])
     WASM_ASSETS_DIR=".\$(prefix)"
     WASM_STDLIB="\$(WASM_ASSETS_DIR)/local/lib/python\$(VERSION)/os.py"
     dnl separate-dwarf does not seem to work in Chrome DevTools Support.
     if test "$Py_DEBUG" = 'true' -o "$ac_sys_emscripten_target" = "browser-debug"; then
-      LDFLAGS_NODIST="$LDFLAGS_NODIST -s ASSERTIONS=1"
+      LDFLAGS_NODIST="$LDFLAGS_NODIST -sASSERTIONS=1"
       LINKFORSHARED="$LINKFORSHARED -gsource-map --emit-symbol-map"
     else
       LINKFORSHARED="$LINKFORSHARED -O2 -g0"
     fi
   ],
   [Emscripten/node*], [
-    LDFLAGS_NODIST="$LDFLAGS_NODIST -s ALLOW_MEMORY_GROWTH=1 -s NODERAWFS=1 -s USE_PTHREADS=1"
-    LINKFORSHARED="-s PROXY_TO_PTHREAD=1 -s EXIT_RUNTIME=1"
+    LDFLAGS_NODIST="$LDFLAGS_NODIST -sALLOW_MEMORY_GROWTH=1 -sNODERAWFS=1 -sUSE_PTHREADS=1"
+    LINKFORSHARED="-sPROXY_TO_PTHREAD=1 -sEXIT_RUNTIME=1"
+    AS_VAR_IF([enable_wasm_dynamic_linking], [yes], [
+      AS_VAR_APPEND([LINKFORSHARED], [" -sMAIN_MODULE=1"])
+    ])
     CFLAGS_NODIST="$CFLAGS_NODIST -pthread"
     if test "$Py_DEBUG" = 'true' -o "$ac_sys_emscripten_target" = "node-debug"; then
-      LDFLAGS_NODIST="$LDFLAGS_NODIST -s ASSERTIONS=1"
+      LDFLAGS_NODIST="$LDFLAGS_NODIST -sASSERTIONS=1"
       LINKFORSHARED="$LINKFORSHARED -gseparate-dwarf --emit-symbol-map"
     else
       LINKFORSHARED="$LINKFORSHARED -O2 -g0"
@@ -1927,6 +1949,12 @@ AS_CASE([$ac_sys_system/$ac_sys_emscripten_target],
   ]
 )
 
+AS_CASE([$enable_wasm_dynamic_linking],
+  [yes], [ac_cv_func_dlopen=yes],
+  [no], [ac_cv_func_dlopen=no],
+  [missing], []
+)
+
 AC_SUBST(BASECFLAGS)
 AC_SUBST(CFLAGS_NODIST)
 AC_SUBST(LDFLAGS_NODIST)
@@ -2929,10 +2957,6 @@ then
 	Linux*|GNU*|QNX*|VxWorks*|Haiku*)
 		LDSHARED='$(CC) -shared'
 		LDCXXSHARED='$(CXX) -shared';;
-	Emscripten*)
-		LDSHARED='$(CC) -shared -s SIDE_MODULE=1'
-		LDCXXSHARED='$(CXX) -shared -s SIDE_MODULE=1'
-    ;;
 	FreeBSD*)
 		if [[ "`$CC -dM -E - </dev/null | grep __ELF__`" != "" ]]
 		then
@@ -2971,15 +2995,30 @@ then
 	SCO_SV*)
 		LDSHARED='$(CC) -Wl,-G,-Bexport'
 		LDCXXSHARED='$(CXX) -Wl,-G,-Bexport';;
+	WASI*)
+		AS_VAR_IF([enable_wasm_dynamic_linking], [yes], [
+			dnl not iplemented yet
+		]);;
 	CYGWIN*)
 		LDSHARED="gcc -shared -Wl,--enable-auto-image-base"
 		LDCXXSHARED="g++ -shared -Wl,--enable-auto-image-base";;
 	*)	LDSHARED="ld";;
 	esac
 fi
+
+dnl Emscripten's emconfigure sets LDSHARED. Set BLDSHARED outside the
+dnl test -z $LDSHARED block to configure BLDSHARED for side module support.
+if test "$enable_wasm_dynamic_linking" = "yes" -a "$ac_sys_system" = "Emscripten"; then
+  BLDSHARED='$(CC) -shared -sSIDE_MODULE=1 -sWASM=1'
+fi
+
 AC_MSG_RESULT($LDSHARED)
 LDCXXSHARED=${LDCXXSHARED-$LDSHARED}
+
+AC_MSG_CHECKING([BLDSHARED flags])
 BLDSHARED=${BLDSHARED-$LDSHARED}
+AC_MSG_RESULT([$BLDSHARED])
+
 # CCSHARED are the C *flags* used to create objects to go into a shared
 # library (module) -- this is only needed for a few systems
 AC_MSG_CHECKING(CCSHARED)
@@ -2998,6 +3037,10 @@ then
 		 fi;;
 	Linux-android*) ;;
 	Linux*|GNU*) CCSHARED="-fPIC";;
+	Emscripten*|WASI*)
+		AS_VAR_IF([enable_wasm_dynamic_linking], [yes], [
+			CCSHARED="-fPIC"
+		]);;
 	FreeBSD*|NetBSD*|OpenBSD*|DragonFly*) CCSHARED="-fPIC";;
 	Haiku*) CCSHARED="-fPIC";;
 	OpenUNIX*|UnixWare*)
@@ -3099,6 +3142,12 @@ then
 		CFLAGSFORSHARED='$(CCSHARED)'
 	esac
 fi
+
+dnl WASM dynamic linking requires -fPIC.
+AS_VAR_IF([enable_wasm_dynamic_linking], [yes], [
+  CFLAGSFORSHARED='$(CCSHARED)'
+])
+
 AC_MSG_RESULT($CFLAGSFORSHARED)
 
 # SHLIBS are libraries (except -lc and -lm) to link to the python shared
@@ -4460,7 +4509,8 @@ PKG_CHECK_MODULES([ZLIB], [zlib >= 1.2.0], [
 ])
 
 if test "$have_zlib" = "yes" -a "$ac_sys_system" = "Emscripten" -a "$ZLIB_LIBS" = "-lz"; then
-  ZLIB_LIBS="-s USE_ZLIB=1"
+  ZLIB_CFLAGS="-sUSE_ZLIB=1"
+  ZLIB_LIBS="-sUSE_ZLIB=1"
 fi
 
 dnl binascii can use zlib for optimized crc32.
@@ -4482,7 +4532,8 @@ PKG_CHECK_MODULES([BZIP2], [bzip2], [have_bzip2=yes], [
 ])
 
 if test "$have_bzip2" = "yes" -a "$ac_sys_system" = "Emscripten" -a "$BZIP2_LIBS" = "-lbz2"; then
-  BZIP2_LIBS="-s USE_BZIP2=1"
+  BZIP2_CFLAGS="-sUSE_BZIP2=1"
+  BZIP2_LIBS="-sUSE_BZIP2=1"
 fi