[PULL 15/18] include/qemu/int128.h: define struct Int128 according to the host endianness

[David Gibson <david@gibson.dropbear.id.au>]

From: Matheus Ferst <matheus.ferst@eldorado.org.br>

Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Matheus Ferst <matheus.ferst@eldorado.org.br>
Message-Id: <20210826141446.2488609-2-matheus.ferst@eldorado.org.br>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 include/qemu/int128.h | 27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/include/qemu/int128.h b/include/qemu/int128.h
index 64500385e3..17436d851d 100644
--- a/include/qemu/int128.h
+++ b/include/qemu/int128.h
@@ -162,24 +162,37 @@ static inline Int128 bswap128(Int128 a)
 
 typedef struct Int128 Int128;
 
+/*
+ * We guarantee that the in-memory byte representation of an
+ * Int128 is that of a host-endian-order 128-bit integer
+ * (whether using this struct or the __int128_t version of the type).
+ * Some code using this type relies on this (eg when copying it into
+ * guest memory or a gdb protocol buffer, or by using Int128 in
+ * a union with other integer types).
+ */
 struct Int128 {
+#ifdef HOST_WORDS_BIGENDIAN
+    int64_t hi;
+    uint64_t lo;
+#else
     uint64_t lo;
     int64_t hi;
+#endif
 };
 
 static inline Int128 int128_make64(uint64_t a)
 {
-    return (Int128) { a, 0 };
+    return (Int128) { .lo = a, .hi = 0 };
 }
 
 static inline Int128 int128_makes64(int64_t a)
 {
-    return (Int128) { a, a >> 63 };
+    return (Int128) { .lo = a, .hi = a >> 63 };
 }
 
 static inline Int128 int128_make128(uint64_t lo, uint64_t hi)
 {
-    return (Int128) { lo, hi };
+    return (Int128) { .lo = lo, .hi = hi };
 }
 
 static inline uint64_t int128_get64(Int128 a)
@@ -210,22 +223,22 @@ static inline Int128 int128_one(void)
 
 static inline Int128 int128_2_64(void)
 {
-    return (Int128) { 0, 1 };
+    return int128_make128(0, 1);
 }
 
 static inline Int128 int128_exts64(int64_t a)
 {
-    return (Int128) { .lo = a, .hi = (a < 0) ? -1 : 0 };
+    return int128_make128(a, (a < 0) ? -1 : 0);
 }
 
 static inline Int128 int128_and(Int128 a, Int128 b)
 {
-    return (Int128) { a.lo & b.lo, a.hi & b.hi };
+    return int128_make128(a.lo & b.lo, a.hi & b.hi);
 }
 
 static inline Int128 int128_or(Int128 a, Int128 b)
 {
-    return (Int128) { a.lo | b.lo, a.hi | b.hi };
+    return int128_make128(a.lo | b.lo, a.hi | b.hi);
 }
 
 static inline Int128 int128_rshift(Int128 a, int n)
-- 
2.31.1