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| author | Lasse Collin <lasse.collin@tukaani.org> | 2023-09-26 13:14:37 +0300 |
|---|---|---|
| committer | Lasse Collin <lasse.collin@tukaani.org> | 2023-09-26 13:50:19 +0300 |
| commit | 9f1444a8a5c0e724b2c7ef83424f642f07a95982 (patch) | |
| tree | 4d5186fafe73df14a419b27f67ae9856dc5ec3ad | |
| parent | CMake: Remove accidental extra newline. (diff) | |
| download | xz-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.ac | 9 |
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.]) |