gh-111225: Link extension modules against libpython on Android (#115780)

Part of the work on PEP 738: Adding Android as a supported platform.

* Rename the LIBPYTHON variable to MODULE_LDFLAGS, to more accurately 
  reflect its purpose.
* Edit makesetup to use MODULE_LDFLAGS when linking extension modules.
* Edit the Makefile so that extension modules depend on libpython on 
  Android and Cygwin.
* Restore `-fPIC` on Android. It was removed several years ago with a 
  note that the toolchain used it automatically, but this is no longer
  the case. Omitting it causes all linker commands to fail with an error
  like `relocation R_AARCH64_ADR_PREL_PG_HI21 cannot be used against
  symbol '_Py_FalseStruct'; recompile with -fPIC`.

Author: mhsmith

Makefile.pre.in

@@ -41,7 +41,7 @@ AR=		@AR@
 READELF=	@READELF@
 SOABI=		@SOABI@
 LDVERSION=	@LDVERSION@
-LIBPYTHON=	@LIBPYTHON@
+MODULE_LDFLAGS=@MODULE_LDFLAGS@
 GITVERSION=	@GITVERSION@
 GITTAG=		@GITTAG@
 GITBRANCH=	@GITBRANCH@
@@ -2917,7 +2917,7 @@ Python/thread.o: @THREADHEADERS@ $(srcdir)/Python/condvar.h
 
 # force rebuild when header file or module build flavor (static/shared) is changed
 MODULE_DEPS_STATIC=Modules/config.c
-MODULE_DEPS_SHARED=$(MODULE_DEPS_STATIC) $(EXPORTSYMS)
+MODULE_DEPS_SHARED=@MODULE_DEPS_SHARED@
 
 MODULE__CURSES_DEPS=$(srcdir)/Include/py_curses.h
 MODULE__CURSES_PANEL_DEPS=$(srcdir)/Include/py_curses.h

Misc/NEWS.d/next/Build/2024-02-21-18-22-49.gh-issue-111225.Z8C3av.rst

@@ -0,0 +1 @@
+Link extension modules against libpython on Android.

Modules/makesetup

@@ -87,18 +87,6 @@ esac
 NL='\
 '
 
-# Setup to link with extra libraries when making shared extensions.
-# Currently, only Cygwin needs this baggage.
-case `uname -s` in
-CYGWIN*) if test $libdir = .
-	 then
-	 	ExtraLibDir=.
-	 else
-	 	ExtraLibDir='$(LIBPL)'
-	 fi
-	 ExtraLibs="-L$ExtraLibDir -lpython\$(LDVERSION)";;
-esac
-
 # Main loop
 for i in ${*-Setup}
 do
@@ -286,7 +274,7 @@ sed -e 's/[ 	]*#.*//' -e '/^[ 	]*$/d' |
 				;;
 			esac
 			rule="$file: $objs"
-			rule="$rule; \$(BLDSHARED) $objs $libs $ExtraLibs -o $file"
+			rule="$rule; \$(BLDSHARED) $objs $libs \$(MODULE_LDFLAGS) -o $file"
 			echo "$rule" >>$rulesf
 		done
 	done

configure

@@ -1360,6 +1360,7 @@ if test $enable_shared = "yes"; then
   case $ac_sys_system in
     CYGWIN*)
       LDLIBRARY='libpython$(LDVERSION).dll.a'
+      BLDLIBRARY='-L. -lpython$(LDVERSION)'
       DLLLIBRARY='libpython$(LDVERSION).dll'
       ;;
     SunOS*)
@@ -3333,7 +3334,6 @@ then
 		 then CCSHARED="-fPIC";
 		 else CCSHARED="+z";
 		 fi;;
-	Linux-android*) ;;
 	Linux*|GNU*) CCSHARED="-fPIC";;
 	Emscripten*|WASI*)
 		AS_VAR_IF([enable_wasm_dynamic_linking], [yes], [
@@ -5888,11 +5888,13 @@ LDVERSION='$(VERSION)$(ABIFLAGS)'
 AC_MSG_RESULT([$LDVERSION])
 
 # On Android and Cygwin the shared libraries must be linked with libpython.
-AC_SUBST([LIBPYTHON])
+AC_SUBST([MODULE_DEPS_SHARED])
+AC_SUBST([MODULE_LDFLAGS])
+MODULE_DEPS_SHARED='$(MODULE_DEPS_STATIC) $(EXPORTSYMS)'
+MODULE_LDFLAGS=''
 if test "$PY_ENABLE_SHARED" = "1" && ( test -n "$ANDROID_API_LEVEL" || test "$MACHDEP" = "cygwin"); then
-  LIBPYTHON="-lpython${VERSION}${ABIFLAGS}"
-else
-  LIBPYTHON=''
+  MODULE_DEPS_SHARED="$MODULE_DEPS_SHARED \$(LDLIBRARY)"
+  MODULE_LDFLAGS="\$(BLDLIBRARY)"
 fi