semihosting/uaccess: Briefly document returned values

Since it is not obvious the get/put_user*() methods
can return an error, add brief docstrings about it.
Also remind to use *unlock_user() when appropriate.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20241212115413.42109-1-philmd@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20250116160306.1709518-3-alex.bennee@linaro.org>

include/semihosting/uaccess.h

@@ -19,41 +19,96 @@
 #include "exec/tswap.h"
 #include "exec/page-protection.h"
 
+/**
+ * get_user_u64:
+ *
+ * Returns: 0 on success, -1 on error.
+ */
 #define get_user_u64(val, addr)                                         \
     ({ uint64_t val_ = 0;                                               \
        int ret_ = cpu_memory_rw_debug(env_cpu(env), (addr),             \
                                       &val_, sizeof(val_), 0);          \
        (val) = tswap64(val_); ret_; })
 
+/**
+ * get_user_u32:
+ *
+ * Returns: 0 on success, -1 on error.
+ */
 #define get_user_u32(val, addr)                                         \
     ({ uint32_t val_ = 0;                                               \
        int ret_ = cpu_memory_rw_debug(env_cpu(env), (addr),             \
                                       &val_, sizeof(val_), 0);          \
        (val) = tswap32(val_); ret_; })
 
+/**
+ * get_user_u8:
+ *
+ * Returns: 0 on success, -1 on error.
+ */
 #define get_user_u8(val, addr)                                          \
     ({ uint8_t val_ = 0;                                                \
        int ret_ = cpu_memory_rw_debug(env_cpu(env), (addr),             \
                                       &val_, sizeof(val_), 0);          \
        (val) = val_; ret_; })
 
+/**
+ * get_user_ual:
+ *
+ * Returns: 0 on success, -1 on error.
+ */
 #define get_user_ual(arg, p) get_user_u32(arg, p)
 
+/**
+ * put_user_u64:
+ *
+ * Returns: 0 on success, -1 on error.
+ */
 #define put_user_u64(val, addr)                                         \
     ({ uint64_t val_ = tswap64(val);                                    \
        cpu_memory_rw_debug(env_cpu(env), (addr), &val_, sizeof(val_), 1); })
 
+/**
+ * put_user_u32:
+ *
+ * Returns: 0 on success, -1 on error.
+ */
 #define put_user_u32(val, addr)                                         \
     ({ uint32_t val_ = tswap32(val);                                    \
        cpu_memory_rw_debug(env_cpu(env), (addr), &val_, sizeof(val_), 1); })
 
+/**
+ * put_user_ual:
+ *
+ * Returns: 0 on success, -1 on error.
+ */
 #define put_user_ual(arg, p) put_user_u32(arg, p)
 
+/**
+ * uaccess_lock_user:
+ *
+ * The returned pointer should be freed using uaccess_unlock_user().
+ */
 void *uaccess_lock_user(CPUArchState *env, target_ulong addr,
                         target_ulong len, bool copy);
+/**
+ * lock_user:
+ *
+ * The returned pointer should be freed using unlock_user().
+ */
 #define lock_user(type, p, len, copy) uaccess_lock_user(env, p, len, copy)
 
+/**
+ * uaccess_lock_user_string:
+ *
+ * The returned string should be freed using uaccess_unlock_user().
+ */
 char *uaccess_lock_user_string(CPUArchState *env, target_ulong addr);
+/**
+ * uaccess_lock_user_string:
+ *
+ * The returned string should be freed using unlock_user().
+ */
 #define lock_user_string(p) uaccess_lock_user_string(env, p)
 
 void uaccess_unlock_user(CPUArchState *env, void *p,