ffsl, ffsll: Fix compilation error on Android.

* lib/string.in.h: On Android as well, include <strings.h>.
* m4/ffsl.m4 (gl_FUNC_FFSL): Use a specific link test instead of
AC_CHECK_FUNCS_ONCE.
* m4/ffsll.m4 (gl_FUNC_FFSLL): Likewise.
* doc/glibc-functions/ffsl.texi: Mention Android problems.
* doc/glibc-functions/ffsll.texi: Likewise.

6 files changed, 61 insertions, 10 deletions

diff --git a/ChangeLog b/ChangeLog
index fc20f7ebe4..59a916a13a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,13 @@
 2023-01-03  Bruno Haible  <bruno@clisp.org>
 
+	ffsl, ffsll: Fix compilation error on Android.
+	* lib/string.in.h: On Android as well, include <strings.h>.
+	* m4/ffsl.m4 (gl_FUNC_FFSL): Use a specific link test instead of
+	AC_CHECK_FUNCS_ONCE.
+	* m4/ffsll.m4 (gl_FUNC_FFSLL): Likewise.
+	* doc/glibc-functions/ffsl.texi: Mention Android problems.
+	* doc/glibc-functions/ffsll.texi: Likewise.
+
 	ffs: Document Android problem.
 	* doc/posix-functions/ffs.texi: Mention Android problem.
 	* m4/ffs.m4: Update comment.
diff --git a/doc/glibc-functions/ffsl.texi b/doc/glibc-functions/ffsl.texi
index 441383cc38..fa80a5cb28 100644
--- a/doc/glibc-functions/ffsl.texi
+++ b/doc/glibc-functions/ffsl.texi
@@ -14,9 +14,12 @@ FreeBSD 5.2.1, NetBSD 9.0, OpenBSD 6.7, Minix 3.1.8, AIX 5.1, HP-UX 11, IRIX 6.5
 @item
 This function is declared in @code{<strings.h>} instead of @code{<string.h>}
 on some platforms:
-AIX 7.2.
+AIX 7.2, Android 13.
 @end itemize
 
 Portability problems not fixed by Gnulib:
 @itemize
+@item
+This function is only defined as an inline function on some platforms:
+Android 13.
 @end itemize
diff --git a/doc/glibc-functions/ffsll.texi b/doc/glibc-functions/ffsll.texi
index 41e701e87e..7912d451fc 100644
--- a/doc/glibc-functions/ffsll.texi
+++ b/doc/glibc-functions/ffsll.texi
@@ -14,7 +14,7 @@ Mac OS X 10.5, FreeBSD 6.0, NetBSD 9.0, OpenBSD 6.7, Minix 3.1.8, AIX 5.1, HP-UX
 @item
 This function is declared in @code{<strings.h>} instead of @code{<string.h>}
 on some platforms:
-AIX 7.2.
+AIX 7.2, Android 13.
 @item
 This function returns completely wrong values on some platforms:
 AIX 7.2 in 32-bit mode.
@@ -22,4 +22,7 @@ AIX 7.2 in 32-bit mode.
 
 Portability problems not fixed by Gnulib:
 @itemize
+@item
+This function is only defined as an inline function on some platforms:
+Android 13.
 @end itemize
diff --git a/lib/string.in.h b/lib/string.in.h
index e993b2fb6f..b2683b6e4c 100644
--- a/lib/string.in.h
+++ b/lib/string.in.h
@@ -59,10 +59,11 @@
 # include <unistd.h>
 #endif
 
-/* AIX 7.2 declares ffsl and ffsll in <strings.h>, not in <string.h>.  */
+/* AIX 7.2 and Android 13 declare ffsl and ffsll in <strings.h>, not in
+   <string.h>.  */
 /* But in any case avoid namespace pollution on glibc systems.  */
 #if ((@GNULIB_FFSL@ || @GNULIB_FFSLL@ || defined GNULIB_POSIXCHECK) \
-     && defined _AIX) \
+     && (defined _AIX || defined __ANDROID__)) \
     && ! defined __GLIBC__
 # include <strings.h>
 #endif
diff --git a/m4/ffsl.m4 b/m4/ffsl.m4
index 1d840e5b80..568e47cdaf 100644
--- a/m4/ffsl.m4
+++ b/m4/ffsl.m4
@@ -1,4 +1,4 @@
-# ffsl.m4 serial 2
+# ffsl.m4 serial 3
 dnl Copyright (C) 2011-2023 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -11,8 +11,26 @@ AC_DEFUN([gl_FUNC_FFSL],
   dnl Persuade glibc <string.h> to declare ffsl().
   AC_REQUIRE([AC_USE_SYSTEM_EXTENSIONS])
 
-  AC_CHECK_FUNCS_ONCE([ffsl])
-  if test $ac_cv_func_ffsl = no; then
+  dnl We can't use AC_CHECK_FUNC here, because ffsl() is defined as a
+  dnl static inline function when compiling for Android 13 or older.
+  dnl But require that ffsl() is declared; otherwise we may be using
+  dnl the GCC built-in function, which leads to warnings
+  dnl "warning: implicit declaration of function 'ffsl'".
+  AC_CACHE_CHECK([for ffsl], [gl_cv_func_ffsl],
+    [AC_LINK_IFELSE(
+       [AC_LANG_PROGRAM(
+          [[#include <string.h>
+            #include <strings.h>
+            long x;
+          ]],
+          [[int (*func) (long) = ffsl;
+            return func (x);
+          ]])
+       ],
+       [gl_cv_func_ffsl=yes],
+       [gl_cv_func_ffsl=no])
+    ])
+  if test $gl_cv_func_ffsl = no; then
     HAVE_FFSL=0
   fi
 ])
diff --git a/m4/ffsll.m4 b/m4/ffsll.m4
index 8414272c6e..d2bffe6e81 100644
--- a/m4/ffsll.m4
+++ b/m4/ffsll.m4
@@ -1,4 +1,4 @@
-# ffsll.m4 serial 3
+# ffsll.m4 serial 4
 dnl Copyright (C) 2011-2023 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -12,8 +12,26 @@ AC_DEFUN([gl_FUNC_FFSLL],
   dnl Persuade glibc <string.h> and AIX <strings.h> to declare ffsll().
   AC_REQUIRE([AC_USE_SYSTEM_EXTENSIONS])
 
-  AC_CHECK_FUNCS_ONCE([ffsll])
-  if test $ac_cv_func_ffsll = yes; then
+  dnl We can't use AC_CHECK_FUNC here, because ffsll() is defined as a
+  dnl static inline function when compiling for Android 13 or older.
+  dnl But require that ffsll() is declared; otherwise we may be using
+  dnl the GCC built-in function, which leads to warnings
+  dnl "warning: implicit declaration of function 'ffsll'".
+  AC_CACHE_CHECK([for ffsll], [gl_cv_func_ffsll],
+    [AC_LINK_IFELSE(
+       [AC_LANG_PROGRAM(
+          [[#include <string.h>
+            #include <strings.h>
+            long long x;
+          ]],
+          [[int (*func) (long long) = ffsll;
+            return func (x);
+          ]])
+       ],
+       [gl_cv_func_ffsll=yes],
+       [gl_cv_func_ffsll=no])
+    ])
+  if test $gl_cv_func_ffsll = yes; then
     dnl Test whether ffsll works.
     dnl On AIX 7.2 in 32-bit mode it is completely broken.
     AC_CACHE_CHECK([whether ffsll works],