buildroot

From 16d88e7813a7739c070a7a1cf6388fd4f236fd99 Mon Sep 17 00:00:00 2001

From: Gustavo Zacarias <gustavo@zacarias.com.ar>

Date: Fri, 31 Jan 2014 06:45:18 -0300

Subject: [PATCHv2] build: find FILE_OFFSET_BITS via array

​

This makes cross-compiling happy, use a trick similar to autoconf's

AC_CHECK_SIZEOF macro.

Basically we make an array:

​

static int array[1 - 2 * !(((long int)(sizeof(off_t))) < 8)];

​

This gives -1 multiplied by the negation of the condition

(sizeof(off_t) < 8) cast to a long int.

So if the condition is true it gives array[(-1 * 0)] (remember the

condition is cast and negated) thus passing a build test with a 0-sized

array.

If it's false it gives array[(-1 * 1)] thus failing with a

negative-sized array.

​

Status: Upstream.

​

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>

---

 lib/ccan/wscript | 11 +++++++----

 1 file changed, 7 insertions(+), 4 deletions(-)

​

diff --git a/lib/ccan/wscript b/lib/ccan/wscript

index 59b8205..81039d0 100644

--- a/lib/ccan/wscript

+++ b/lib/ccan/wscript

@@ -127,15 +127,18 @@ def configure(conf):

     # Only check for FILE_OFFSET_BITS=64 if off_t is normally small:

     # use raw routines because wrappers include previous _GNU_SOURCE

     # or _FILE_OFFSET_BITS defines.

+    # The math for these tests is:

+    # array[-1 * !((int)(condition)) ] (condition is true) = array[0] = builds

+    # array[-1 * !((int)(condition)) ] (condition is false) = array[-1] = fails

     conf.check(fragment="""#include <sys/types.h>

-               int main(void) { return !(sizeof(off_t) < 8); }""",

-               execute=True, msg='Checking for small off_t',

+               int main(void) { static int test_array[1 - 2 * !(((long int)(sizeof(off_t))) < 8)]; }""",

+               msg='Checking for small off_t',

                define_name='SMALL_OFF_T')

     # Unreliable return value above, hence use define.

     if conf.CONFIG_SET('SMALL_OFF_T'):

         conf.check(fragment="""#include <sys/types.h>

-                   int main(void) { return !(sizeof(off_t) >= 8); }""",

-                   execute=True, msg='Checking for -D_FILE_OFFSET_BITS=64',

+          int main(void) { static int test_array[1 - 2 * !(((long int)(sizeof(off_t))) >= 8)]; }""",

+                   msg='Checking for -D_FILE_OFFSET_BITS=64',

                    ccflags='-D_FILE_OFFSET_BITS=64',

                    define_name='HAVE_FILE_OFFSET_BITS')

-- 

1.8.3.2

​