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authorLasse Collin <lasse.collin@tukaani.org>2023-09-26 13:14:37 +0300
committerLasse Collin <lasse.collin@tukaani.org>2023-09-26 13:50:19 +0300
commit9f1444a8a5c0e724b2c7ef83424f642f07a95982 (patch)
tree4d5186fafe73df14a419b27f67ae9856dc5ec3ad
parentCMake: Remove accidental extra newline. (diff)
downloadxz-9f1444a8a5c0e724b2c7ef83424f642f07a95982.tar.xz
Build: Silence two Autoconf warnings.
There were two uses of AC_COMPILE_IFELSE that didn't use AC_LANG_SOURCE and Autoconf warned about these. The omission had been intentional but it turned out that this didn't do what I thought it would. Autoconf 2.71 manual gives an impression that AC_LANG_SOURCE inserts all #defines that have been made with AC_DEFINE so far (confdefs.h). The idea was that omitting AC_LANG_SOURCE would mean that only the exact code included in the AC_COMPILE_IFELSE call would be compiled. With C programs this is not true: the #defines get added without AC_LANG_SOURCE too. There seems to be no neat way to avoid this. Thus, with the C language at least, adding AC_LANG_SOURCE makes no other difference than silencing a warning from Autoconf. The generated "configure" remains identical. (Docs of AC_LANG_CONFTEST say that the #defines have been inserted since Autoconf 2.63b and that AC_COMPILE_IFELSE uses AC_LANG_CONFTEST. So the behavior is documented if one also reads the docs of macros that one isn't calling directly.) Any extra code, including #defines, can cause problems for these two tests because these tests must use -Werror. CC=clang CFLAGS=-Weverything is the most extreme example. It enables -Wreserved-macro-identifier which warns about #define __EXTENSIONS__ 1 because it begins with two underscores. It's possible to write a test file that passes -Weverything but it becomes impossible when Autoconf inserts confdefs.h. So this commit adds AC_LANG_SOURCE to silence Autoconf warnings. A different solution is needed for -Werror tests.
-rw-r--r--configure.ac9
1 files changed, 4 insertions, 5 deletions
diff --git a/configure.ac b/configure.ac
index 78d6e8ac..83d28b85 100644
--- a/configure.ac
+++ b/configure.ac
@@ -834,15 +834,14 @@ AC_C_BIGENDIAN
# Use -Werror because some compilers accept unknown attributes and just
# give a warning. If it works this should give no warnings, even
# clang -Weverything should be fine.
-# dnl This doesn't need AC_LANG_SOURCE, minimal code is enough.
AC_MSG_CHECKING([if __attribute__((__constructor__)) can be used])
have_func_attribute_constructor=no
OLD_CFLAGS="$CFLAGS"
CFLAGS="$CFLAGS -Werror"
-AC_COMPILE_IFELSE([
+AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
__attribute__((__constructor__))
static void my_constructor_func(void) { return; }
-], [
+]])], [
AC_DEFINE([HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR], [1],
[Define to 1 if __attribute__((__constructor__))
is supported for functions.])
@@ -878,12 +877,12 @@ if test "x$enable_ifunc" = xyes ; then
OLD_CFLAGS="$CFLAGS"
CFLAGS="$CFLAGS -Werror"
AC_MSG_CHECKING([if __attribute__((__ifunc__())) can be used])
- AC_COMPILE_IFELSE([
+ AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
static void func(void) { return; }
static void (*resolve_func (void)) (void) { return func; }
void func_ifunc (void)
__attribute__((__ifunc__("resolve_func")));
- ], [
+ ]])], [
AC_DEFINE([HAVE_FUNC_ATTRIBUTE_IFUNC], [1],
[Define to 1 if __attribute__((__ifunc__()))
is supported for functions.])