sanity.bbclass:check if necessary to add march to BUILD_CFLAGS

1, There are a set of GCC built-in functions for atomic memory access. The
definition given in the Intel documentation allows only for the use of the
types int, long, long long as well as their unsigned counterparts. GCC will
allow any integral scalar or pointer type that is 1, 2, 4, 8 or 16 bytes in
length, suffix `_n' where n is the size of the data type.Such as:
__sync_fetch_and_add_n
__sync_fetch_and_sub_n
__sync_fetch_and_or_n
__sync_fetch_and_and_n
__sync_fetch_and_xor_n
__sync_fetch_and_nand_n
The above builtins are intended to be compatible with those described in the
Intel Itanium Processor-specific Application Binary Interface, section 7.4.

2, The glib-2.0-native and qemu-native invoke the above builtin function with
suffix `_4', and glib-2.0-native uses __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4 to
test the existance.

3, Not all above builtin functions are supported by all target processors.Such
as i386 does not support the functions with suffix `_4', but i486 or later
support.

4, Prior to GCC 4.5, on the Intel's processor, the default arch is i386 unless
GCC is built with the --with-arch switch. Since GCC 4.5 the default arch is
implied by the target.

5, If your host GCC is older than 4.5 and it is built without the --with-arch
switch, when you use the GCC to compile target, you should specify -march to
tell GCC what the target's arch is, otherwise i386 is used as default.

Above all, when use older GCC to compile glib-2.0-native or glib-2.0-native,
and the GCC incorrectly uses i386 as default, the above builtin function
with suffix `_4' is not referenced. We should have a check in sanity.bbclass
to tell the user if necessary to add march to BUILD_CFLAGS in this situation.

http://gcc.gnu.org/onlinedocs/gcc-4.7.2/gcc/_005f_005fsync-Builtins.html#_005f_005fsync-Builtins
http://gcc.gnu.org/ml/gcc-help/2009-06/msg00037.html
http://gcc.gnu.org/gcc-4.5/changes.html
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47460
http://llvm.org/bugs/show_bug.cgi?id=11174
http://download.intel.com/design/itanium/downloads/245370.pdf

[YOCTO #3563]

Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>

0 files changed, 0 insertions, 0 deletions