gh-131842: Allow to pass custom CFLAGS and LDFLAGS to the compilation of builtin extension modules

Author: pablogsal

Doc/using/configure.rst

@@ -1401,7 +1401,7 @@ Compiler flags
    Compiler flags to build a standard library extension module as a built-in
    module, like the :mod:`posix` module.
 
-   Default: ``$(PY_STDMODULE_CFLAGS) -DPy_BUILD_CORE_BUILTIN``.
+   Default: ``$(BUILTIN_MODULE_CFLAGS) $(PY_STDMODULE_CFLAGS) -DPy_BUILD_CORE_BUILTIN``.
 
    .. versionadded:: 3.8
 
@@ -1495,6 +1495,15 @@ Linker flags
 
    .. versionadded:: 3.8
 
+.. envvar:: PY_BUILTIN_MODULE_LDFLAHS
+
+   Linker flags to build a standard library extension module as a built-in
+   module, like the :mod:`posix` module.
+
+   Default: ``$(BUILTIN_MODULE_LDFLAGS)`.
+
+   .. versionadded:: 3.13
+
 
 .. rubric:: Footnotes
 

Makefile.pre.in

@@ -119,8 +119,11 @@ ARFLAGS=	@ARFLAGS@
 # Extra C flags added for building the interpreter object files.
 CFLAGSFORSHARED=@CFLAGSFORSHARED@
 # C flags used for building the interpreter object files
+CFLAGS_BUILTIN_MODULE= @CFLAGS_BUILTIN_MODULE@
+LDFLAGS_BUILTIN_MODULE= @LDFLAGS_BUILTIN_MODULE@
 PY_STDMODULE_CFLAGS= $(PY_CFLAGS) $(PY_CFLAGS_NODIST) $(PY_CPPFLAGS) $(CFLAGSFORSHARED)
-PY_BUILTIN_MODULE_CFLAGS= $(PY_STDMODULE_CFLAGS) -DPy_BUILD_CORE_BUILTIN
+PY_BUILTIN_MODULE_CFLAGS= $(CFLAGS_BUILTIN_MODULE) $(PY_STDMODULE_CFLAGS) -DPy_BUILD_CORE_BUILTIN
+PY_BUILTIN_MODULE_LDFLAGS= $(LDFLAGS_BUILTIN_MODULE)
 PY_CORE_CFLAGS=	$(PY_STDMODULE_CFLAGS) -DPy_BUILD_CORE
 # Linker flags used for building the interpreter object files
 PY_CORE_LDFLAGS=$(PY_LDFLAGS) $(PY_LDFLAGS_NODIST)

Misc/NEWS.d/next/Build/2025-03-28-15-34-49.gh-issue-131842.HB2qep.rst

@@ -0,0 +1,2 @@
+Allow to pass custom ``CFLAGS`` and ``LDFLAGS`` to the compilation of
+builtin extension modules. Patch by Pablo Galindo

Modules/makesetup

@@ -274,7 +274,8 @@ sed -e 's/[ 	]*#.*//' -e '/^[ 	]*$/d' |
 				;;
 			esac
 			rule="$file: $objs"
-			rule="$rule; \$(BLDSHARED) $objs $libs \$(LIBPYTHON) -o $file"
+			ldd="\$(BLDSHARED) \$(PY_BUILTIN_MODULE_LDFLAGS)"
+			rule="$rule; $ldd $objs $libs \$(LIBPYTHON) -o $file"
 			echo "$rule" >>$rulesf
 		done
 	done

configure

@@ -2432,7 +2432,9 @@ AS_CASE([$enable_wasm_dynamic_linking],
 
 AC_SUBST([BASECFLAGS])
 AC_SUBST([CFLAGS_NODIST])
+AC_SUBST([CFLAGS_BUILTIN_MODULE])
 AC_SUBST([LDFLAGS_NODIST])
+AC_SUBST([LDFLAGS_BUILTIN_MODULE])
 AC_SUBST([LDFLAGS_NOLTO])
 AC_SUBST([WASM_ASSETS_DIR])
 AC_SUBST([WASM_STDLIB])