buildroot

Improve the ARM detection to work on Thumb-only architecture

​

The ARM-specific assembly code doesn't build on Thumb-only

architectures such as ARMv7-M, but the configure script assumes that

if the host tuple is arm*, then it can build and use the ARM optimized

code.

​

This patch improves the configure.ac detection logic, by building one

of the instruction of the optimized assembly code, and using this to

decide whether or not the optimizations should be enabled.

​

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

​

Index: b/configure.ac

===================================================================

--- a/configure.ac

+++ b/configure.ac

@@ -101,8 +101,10 @@

     alpha*)

    AC_DEFINE([ARCH_ALPHA],,[alpha architecture]);;

     arm*)

-   arm_conditional=:

-   AC_DEFINE([ARCH_ARM],,[ARM architecture]);;

+   AC_TRY_LINK([], [asm(".syntax divided\nstmfd sp!,{r4-r11,lr}")],

+        [AC_DEFINE([ARCH_ARM],,[ARM architecture])

+         use_arm_optimization=yes],

+        [use_arm_optimization=no])

     esac

 elif test x"$CC" = x"tendracc"; then

     dnl TenDRA portability checking compiler

@@ -122,7 +124,7 @@

     esac

 fi

-AM_CONDITIONAL(ARCH_ARM, ${arm_conditional})

+AM_CONDITIONAL(ARCH_ARM, test "${use_arm_optimization}" = "yes")

 dnl Checks for libtool - this must be done after we set cflags

 AC_LIBTOOL_WIN32_DLL