bswap: Add new stn_*_p() and ldn_*_p() memory access functions

There's a common pattern in QEMU where a function needs to perform
a data load or store of an N byte integer in a particular endianness.
At the moment this is handled by doing a switch() on the size and
calling the appropriate ld*_p or st*_p function for each size.

Provide a new family of functions ldn_*_p() and stn_*_p() which
take the size as an argument and do the switch() themselves.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20180611171007.4165-2-peter.maydell@linaro.org

docs/devel/loads-stores.rst

@@ -53,9 +53,24 @@ The ``_{endian}`` infix is omitted for target-endian accesses.
 The target endian accessors are only available to source
 files which are built per-target.
 
+There are also functions which take the size as an argument:
+
+load: ``ldn{endian}_p(ptr, sz)``
+
+which performs an unsigned load of ``sz`` bytes from ``ptr``
+as an ``{endian}`` order value and returns it in a uint64_t.
+
+store: ``stn{endian}_p(ptr, sz, val)``
+
+which stores ``val`` to ``ptr`` as an ``{endian}`` order value
+of size ``sz`` bytes.
+
+
 Regexes for git grep
  - ``\<ldf\?[us]\?[bwlq]\(_[hbl]e\)\?_p\>``
  - ``\<stf\?[bwlq]\(_[hbl]e\)\?_p\>``
+ - ``\<ldn_\([hbl]e\)?_p\>``
+ - ``\<stn_\([hbl]e\)?_p\>``
 
 ``cpu_{ld,st}_*``
 ~~~~~~~~~~~~~~~~~

include/exec/cpu-all.h

@@ -133,6 +133,8 @@ static inline void tswap64s(uint64_t *s)
 #define stq_p(p, v) stq_be_p(p, v)
 #define stfl_p(p, v) stfl_be_p(p, v)
 #define stfq_p(p, v) stfq_be_p(p, v)
+#define ldn_p(p, sz) ldn_be_p(p, sz)
+#define stn_p(p, sz, v) stn_be_p(p, sz, v)
 #else
 #define lduw_p(p) lduw_le_p(p)
 #define ldsw_p(p) ldsw_le_p(p)
@@ -145,6 +147,8 @@ static inline void tswap64s(uint64_t *s)
 #define stq_p(p, v) stq_le_p(p, v)
 #define stfl_p(p, v) stfl_le_p(p, v)
 #define stfq_p(p, v) stfq_le_p(p, v)
+#define ldn_p(p, sz) ldn_le_p(p, sz)
+#define stn_p(p, sz, v) stn_le_p(p, sz, v)
 #endif
 
 /* MMU memory access macros */

include/qemu/bswap.h

@@ -290,6 +290,15 @@ typedef union {
  * For accessors that take a guest address rather than a
  * host address, see the cpu_{ld,st}_* accessors defined in
  * cpu_ldst.h.
+ *
+ * For cases where the size to be used is not fixed at compile time,
+ * there are
+ *  stn{endian}_p(ptr, sz, val)
+ * which stores @val to @ptr as an @endian-order number @sz bytes in size
+ * and
+ *  ldn{endian}_p(ptr, sz)
+ * which loads @sz bytes from @ptr as an unsigned @endian-order number
+ * and returns it in a uint64_t.
  */
 
 static inline int ldub_p(const void *ptr)
@@ -495,6 +504,49 @@ static inline unsigned long leul_to_cpu(unsigned long v)
 #endif
 }
 
+/* Store v to p as a sz byte value in host order */
+#define DO_STN_LDN_P(END) \
+    static inline void stn_## END ## _p(void *ptr, int sz, uint64_t v)  \
+    {                                                                   \
+        switch (sz) {                                                   \
+        case 1:                                                         \
+            stb_p(ptr, v);                                              \
+            break;                                                      \
+        case 2:                                                         \
+            stw_ ## END ## _p(ptr, v);                                  \
+            break;                                                      \
+        case 4:                                                         \
+            stl_ ## END ## _p(ptr, v);                                  \
+            break;                                                      \
+        case 8:                                                         \
+            stq_ ## END ## _p(ptr, v);                                  \
+            break;                                                      \
+        default:                                                        \
+            g_assert_not_reached();                                     \
+        }                                                               \
+    }                                                                   \
+    static inline uint64_t ldn_## END ## _p(const void *ptr, int sz)    \
+    {                                                                   \
+        switch (sz) {                                                   \
+        case 1:                                                         \
+            return ldub_p(ptr);                                         \
+        case 2:                                                         \
+            return lduw_ ## END ## _p(ptr);                             \
+        case 4:                                                         \
+            return (uint32_t)ldl_ ## END ## _p(ptr);                    \
+        case 8:                                                         \
+            return ldq_ ## END ## _p(ptr);                              \
+        default:                                                        \
+            g_assert_not_reached();                                     \
+        }                                                               \
+    }
+
+DO_STN_LDN_P(he)
+DO_STN_LDN_P(le)
+DO_STN_LDN_P(be)
+
+#undef DO_STN_LDN_P
+
 #undef le_bswap
 #undef be_bswap
 #undef le_bswaps