Re: boot-time: straighten code

[Bruno Haible <bruno@clisp.org>]

Po Lu wrote:
> During the automated build of the Android port, the following errors
> were encountered with the Android NDK r10b and __ANDROID_API__ set to 8
> (which is the oldest configuration Emacs supports.)...
> 
> In file included from boot-time.c:54:0:
> boot-time-aux.h: In function 'get_linux_uptime':
> boot-time-aux.h:70:3: error: implicit declaration of function 'sysinfo' [-Werror=implicit-function-declaration]
>    if (sysinfo (&info) >= 0)
>    ^

Should be fixed by the patch below.

Paul Eggert wrote:
> Gnulib should bypass sysinfo unless it's available.

Yes. Note that it's available in Android libc already at API level 3. It's only
the declaration that was added in API level 9.

Also, if we write '#if HAVE_DECL_SYSINFO' instead of '9 <= __ANDROID_API__',
the change might be helpful also with other Linux-based libcs that may be
developed in the future.


2023-08-13  Bruno Haible  <bruno@clisp.org>

	readutmp, boot-time: Fix compilation error on Android API 8.
	Reported by Po Lu in
	<https://lists.gnu.org/archive/html/bug-gnulib/2023-08/msg00108.html>.
	* m4/readutmp.m4 (gl_PREREQ_READUTMP_H): Test whether sysinfo is
	declared.
	* lib/boot-time-aux.h (get_linux_uptime): Invoke sysinfo only if it is
	declared.
	* doc/glibc-functions/sysinfo.texi: Mention the Android problem.

diff --git a/doc/glibc-functions/sysinfo.texi b/doc/glibc-functions/sysinfo.texi
index 3b1ade31a6..16e12b12ac 100644
--- a/doc/glibc-functions/sysinfo.texi
+++ b/doc/glibc-functions/sysinfo.texi
@@ -17,4 +17,7 @@
 @item
 This function is missing on some platforms:
 macOS 11.1, FreeBSD 13.0, NetBSD 9.0, OpenBSD 6.7, Minix 3.1.8, AIX 5.1, Cygwin 1.7.9, mingw, MSVC 14.
+@item
+This function is not declared and thus not part of the Android API
+for Android API levels < 9.
 @end itemize
diff --git a/lib/boot-time-aux.h b/lib/boot-time-aux.h
index 348611fc85..e59a0fd03c 100644
--- a/lib/boot-time-aux.h
+++ b/lib/boot-time-aux.h
@@ -65,6 +65,7 @@ get_linux_uptime (struct timespec *p_uptime)
     }
 # endif
 
+# if HAVE_DECL_SYSINFO /* not available in Android API < 9 */
   /* The sysinfo call returns the uptime with a resolution of 1 sec only.  */
   struct sysinfo info;
   if (sysinfo (&info) >= 0)
@@ -73,6 +74,7 @@ get_linux_uptime (struct timespec *p_uptime)
       p_uptime->tv_nsec = 0;
       return 0;
     }
+# endif
 
   return -1;
 }
diff --git a/m4/readutmp.m4 b/m4/readutmp.m4
index 9dffe981b8..0a47f4bb77 100644
--- a/m4/readutmp.m4
+++ b/m4/readutmp.m4
@@ -1,4 +1,4 @@
-# readutmp.m4 serial 29
+# readutmp.m4 serial 30
 dnl Copyright (C) 2002-2023 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -103,6 +103,10 @@ AC_DEFUN_ONCE([gl_PREREQ_READUTMP_H]
     AC_CHECK_MEMBERS([struct utmp.ut_exit.e_termination],,,[$utmp_includes])
   fi
 
+  AC_CHECK_DECLS([sysinfo],,,[[
+    #include <sys/sysinfo.h>
+    ]])
+
   AC_CHECK_HEADERS_ONCE([sys/param.h])
   dnl <sys/sysctl.h> requires <sys/param.h> on OpenBSD 4.0.
   AC_CHECK_HEADERS([sys/sysctl.h],,,