configure: force o32 ABI on MIPS

GRUB code expects O32 or N32. N32 is less tested than O32, so we prefer to
compile with O32. Some systems (e.g. GNU Guix) default to using newer
n64 or n32 ABI. Try to find suitable options to force o32.

For GCC this is simply -mabi=32. While clang supports this option as well,
o32 ABI is valid for MIPS target and n32/64 ABI are valid for MIPS64 target
only, so use "-target mips/mipsel -mabi=32".

Reported-By: Mark H Weaver <mhw@netris.org>
Also-By: Mark H Weaver <mhw@netris.org>

diff --git a/configure.ac b/configure.ac
index c864311f772295980b1423bd47a4a931a139e524..7bac865609fe17b9cc0b6488452c9be5c4ca4611 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -597,6 +597,40 @@ int main (void);
   TARGET_LDFLAGS="$TARGET_LDFLAGS $grub_cv_target_cc_big_endian"
 fi
 
+# GRUB code is N32-compliant but it's experimental and we would prefer to
+# avoid having too much variety when it doesn't result in any real improvement.
+# Moreover N64 isn't supported.
+if test "x$target_cpu" = xmips || test "x$target_cpu" = xmipsel ; then
+  AC_CACHE_CHECK([for options to force MIPS o32 ABI], grub_cv_target_cc_mips_o32_abi, [
+    grub_cv_target_cc_mips_o32_abi=no
+    for arg in "" "-mabi=32" "-target $target_cpu -mabi=32" ; do
+      if test x"$grub_cv_target_cc_mips_o32_abi" != xno ; then
+        break
+      fi
+      CFLAGS="$TARGET_CFLAGS $arg -Werror"
+      AC_LINK_IFELSE([AC_LANG_PROGRAM([[
+#if !defined(_ABIO32) || !defined(_MIPS_SIM) || (_MIPS_SIM != _ABIO32)
+#error not o32 ABI
+#endif
+asm (".globl start; start:");
+asm (".globl _start; _start:");
+asm (".globl __start; __start:");
+void __main (void);
+void __main (void) {}
+int main (void);
+]], [[]])],
+                       [grub_cv_target_cc_mips_o32_abi="$arg"], [])
+    done
+  ])
+
+  if test x"$grub_cv_target_cc_mips_o32_abi" = xno ; then
+    AC_MSG_ERROR([could not force MIPS o32 ABI])
+  fi
+
+  TARGET_CFLAGS="$TARGET_CFLAGS $grub_cv_target_cc_mips_o32_abi"
+  TARGET_CCASFLAGS="$TARGET_CCASFLAGS $grub_cv_target_cc_mips_o32_abi"
+fi
+
 AC_CACHE_CHECK([for options to compile assembly], [grub_cv_cc_target_asm_compile], [
 test_program=
 case "x$target_cpu-$platform" in