On 10/13/22 15:43, Michal Privoznik wrote:
When determining the endiandness of the target architecture we're
building for a small program is compiled, which in an obfuscated
way declares two strings. Then, we look which string is in
correct order (using strings binary) and deduct the endiandness.
But using the strings binary is problematic, because it's part of
toolchain (strings is just a symlink to
x86_64-pc-linux-gnu-strings or llvm-strings). And when
(cross-)compiling, it requires users to set the symlink to the
correct toolchain.
Fortunately, we have a better alternative anyways. We can mimic
what compiler.h is already doing: comparing __BYTE_ORDER__
against values for little/big endiandness.
Bug: https://bugs.gentoo.org/876933
Signed-off-by: Michal Privoznik <mpriv...@redhat.com>
---
v2 of:
https://lists.gnu.org/archive/html/qemu-devel/2022-10/msg02054.html
diff to v1:
- Fixed reversed logic
- Ditched custom compiler macros in favor of __BYTE_ORDER__
configure | 33 +++++++++++++++++----------------
1 file changed, 17 insertions(+), 16 deletions(-)
diff --git a/configure b/configure
index 45ee6f4eb3..2ac26c6978 100755
--- a/configure
+++ b/configure
@@ -1423,30 +1423,31 @@ if test "$tcg" = "enabled"; then
git_submodules="$git_submodules tests/fp/berkeley-softfloat-3"
fi
-# ---
+##########################################
# big/little endian test
cat > $TMPC << EOF
-#include <stdio.h>
-short big_endian[] = { 0x4269, 0x4765, 0x4e64, 0x4961, 0x4e00, 0, };
-short little_endian[] = { 0x694c, 0x7454, 0x654c, 0x6e45, 0x6944, 0x6e41, 0, };
-int main(int argc, char *argv[])
-{
- return printf("%s %s\n", (char *)big_endian, (char *)little_endian);
-}
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
#if defined __BYTE_ORDER__ && ...
+# error LITTLE
+#endif
+int main(void) { return 0; }
EOF
if compile_prog ; then
And then you need to check if it *fails* (i.e. "if ! compile_prog ; then
bigendian=no", and likewise below for the big-endian test). This way if
the macro is not defined both tests will compile successfully and you'll
print the error here:
+ if compile_prog ; then
+ bigendian="no"
+ else
echo big/little test failed
exit 1
+ fi
fi
You can test it by misspelling __BYTE_ORDER__ intentionally.
Thanks,
Paolo
