configure.ac: detect unusable termio operations

Some termio operations are not actually usable on some
architectures. For example, the TCGETA, TCSETA, TCSETAF and TCSETAW
are defined with a reference to "struct termio" on alpha, hppa and
sparc64, but "struct termio" is no longer defined since glibc 2.42,
causing a build failure.

Instead of using those operations as soon as they are defined, this
commit checks more carefully that they are actually usable. Such a
check cannot be done with the standard AC_CHECK_DECL() m4 macro, as
this macro only checks that the #define exists, not that it is
actually usable (i.e builds properly). Therefore, we introduce a
PY_CHECK_CONSTANT() m4 macro, that verifies that the constant is
actually usable.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

Author: tpetazzoni

Misc/NEWS.d/next/Build/2025-12-07-15-06-37.gh-issue-142379.7vvmGc.rst

@@ -0,0 +1,8 @@
+Some termio operations are not actually usable on some architectures. For
+example, the TCGETA, TCSETA, TCSETAF and TCSETAW are defined with a
+reference to "struct termio" on alpha, hppa and sparc64, but "struct termio"
+is no longer defined since glibc 2.42, causing a build failure.
+
+Instead of using those operations as soon as they are defined, this commit
+checks more carefully that they are actually usable. This is done using a
+new m4 macro PY_CHECK_CONSTANT.

Modules/termios.c

@@ -1116,7 +1116,7 @@ static struct constant {
 #ifdef TCFLSH
     {"TCFLSH", TCFLSH},
 #endif
-#ifdef TCGETA
+#if defined(HAVE_TCGETA)
     {"TCGETA", TCGETA},
 #endif
 #ifdef TCGETS
@@ -1128,13 +1128,13 @@ static struct constant {
 #ifdef TCSBRKP
     {"TCSBRKP", TCSBRKP},
 #endif
-#ifdef TCSETA
+#if defined(HAVE_TCSETA)
     {"TCSETA", TCSETA},
 #endif
-#ifdef TCSETAF
+#if defined(HAVE_TCSETAF)
     {"TCSETAF", TCSETAF},
 #endif
-#ifdef TCSETAW
+#if defined(HAVE_TCSETAW)
     {"TCSETAW", TCSETAW},
 #endif
 #ifdef TCSETS

configure

@@ -95,6 +95,26 @@ AC_DEFUN([PY_CHECK_EMSCRIPTEN_PORT], [
   AS_VAR_POPDEF([py_libs])
 ])
 
+dnl PY_CHECK_CONSTANT(TYPE, CONSTANT, [INCLUDES])
+dnl Checks whether the constant exists and is actually usable (unlike
+dnl AC_CHECK_DECL that only checks if the constant exists)
+AC_DEFUN([PY_CHECK_CONSTANT],
+[
+  AC_MSG_CHECKING([for $2])
+  AC_COMPILE_IFELSE(
+    [AC_LANG_PROGRAM(
+       [$3],
+       [[
+         $1 val = $2;
+       ]]
+     )],
+    [AC_MSG_RESULT([yes])
+     AC_DEFINE([HAVE_$2], [1],
+               [Define this if $2 is usable])],
+    [AC_MSG_RESULT([no])]
+  )
+])
+
 AC_SUBST([BASECPPFLAGS])
 if test "$srcdir" != . -a "$srcdir" != "$(pwd)"; then
     # If we're building out-of-tree, we need to make sure the following
@@ -8245,6 +8265,12 @@ AC_SUBST([JIT_STENCILS_H])
 # substitute multiline block, must come after last PY_STDLIB_MOD()
 AC_SUBST([MODULE_BLOCK])
 
+# ioctls used by Modules/termios.c but not usable on all platforms
+PY_CHECK_CONSTANT([long], [TCGETA], [#include <sys/ioctl.h>])
+PY_CHECK_CONSTANT([long], [TCSETA], [#include <sys/ioctl.h>])
+PY_CHECK_CONSTANT([long], [TCSETAF], [#include <sys/ioctl.h>])
+PY_CHECK_CONSTANT([long], [TCSETAW], [#include <sys/ioctl.h>])
+
 # generate output files
 AC_CONFIG_FILES(m4_normalize([
   Makefile.pre

configure.ac

@@ -1524,9 +1524,21 @@
 /* Define to 1 if you have the <sys/xattr.h> header file. */
 #undef HAVE_SYS_XATTR_H
 
+/* Define this if TCGETA is usable */
+#undef HAVE_TCGETA
+
 /* Define to 1 if you have the 'tcgetpgrp' function. */
 #undef HAVE_TCGETPGRP
 
+/* Define this if TCSETA is usable */
+#undef HAVE_TCSETA
+
+/* Define this if TCSETAF is usable */
+#undef HAVE_TCSETAF
+
+/* Define this if TCSETAW is usable */
+#undef HAVE_TCSETAW
+
 /* Define to 1 if you have the 'tcsetpgrp' function. */
 #undef HAVE_TCSETPGRP