[Minios-devel] [UNIKRAFT PATCH 3/3] lib/syscall_shim: `UK_(LL)SYSCALL_R_DEFINE()`: Use given return type

[Simon Kuenzer <simon.kuenzer@xxxxxxxxx>]

Instead of declaring the return type for `UK_(LL)SYSCALL_R_DEFINE()`
functions as `long`, the user-given return type is used. In general,
this is done for convenience. Whenever a system call implementation
uses pointers as return type, the helpers defined in `<uk/errptr.h>`
can be used to encapsulate error codes.

Signed-off-by: Simon Kuenzer <simon.kuenzer@xxxxxxxxx>
---
 doc/guides/developers-app.rst         | 15 +++++++--------
 lib/syscall_shim/include/uk/syscall.h | 11 ++++++-----
 2 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/doc/guides/developers-app.rst b/doc/guides/developers-app.rst
index f14ed5a2..57dcad92 100644
--- a/doc/guides/developers-app.rst
+++ b/doc/guides/developers-app.rst
@@ -391,19 +391,18 @@ Example:
 
     UK_SYSCALL_R_DEFINE(ssize_t, write, int, fd, const void *, buf, size_t, 
count)
     {
-        long ret;
+        ssize_t ret;
 
-        ret = (long) vfs_do_write(fd, buf, count);
+        ret = vfs_do_write(fd, buf, count);
         if (ret < 0) {
             return -EFAULT;
         }
         return ret;
     }
 
-Please note that in the raw case (``UK_SYSCALL_R_DEFINE``), the return type
-within your code block is always ``long``. The specified return type as
-parameter to the macro will be used for the libc-style wrapper. However, the
-input parameters are defined with the actual type for your code block.
+Please note that in the raw case (``UK_SYSCALL_R_DEFINE``), errors are always
+returned as negative value. Whenever the return type is a pointer value, the
+helpers defined in `<uk/errptr.h>` can be used to forward error codes.
 
 Both macros create the following three symbols:
 
@@ -432,9 +431,9 @@ libc-style wrapper on top:
 
     UK_LLSYSCALL_R_DEFINE(ssize_t, write, int, fd, const void *, buf, size_t, 
count)
     {
-        long ret;
+        ssize_t ret;
 
-        ret = (long) vfs_do_write(fd, buf, count);
+        ret = vfs_do_write(fd, buf, count);
         if (ret < 0) {
             return -EFAULT;
         }
diff --git a/lib/syscall_shim/include/uk/syscall.h 
b/lib/syscall_shim/include/uk/syscall.h
index 6ee139fa..aafe20a7 100644
--- a/lib/syscall_shim/include/uk/syscall.h
+++ b/lib/syscall_shim/include/uk/syscall.h
@@ -39,6 +39,7 @@
 
 #include <uk/config.h>
 #include <uk/essentials.h>
+#include <uk/errptr.h>
 #include <errno.h>
 #include <uk/print.h>
 
@@ -192,20 +193,20 @@ typedef long uk_syscall_arg_t;
        {                                                               \
                long ret = rname(                                       \
                        UK_ARG_MAPx(x, UK_S_ARG_CAST_LONG, __VA_ARGS__)); \
-               if (ret < 0) {                                          \
-                       errno = (int) -ret;                             \
+               if (ret < 0 && PTRISERR(ret)) {                         \
+                       errno = (int) PTR2ERR(ret);                     \
                        return -1;                                      \
                }                                                       \
                return ret;                                             \
        }                                                               \
-       static inline long __##rname(UK_ARG_MAPx(x, UK_S_ARG_ACTUAL,    \
+       static inline rtype __##rname(UK_ARG_MAPx(x, UK_S_ARG_ACTUAL,   \
                                                 __VA_ARGS__));         \
        long rname(UK_ARG_MAPx(x, UK_S_ARG_LONG, __VA_ARGS__))          \
        {                                                               \
-               return __##rname(                                       \
+               return (long) __##rname(                                \
                        UK_ARG_MAPx(x, UK_S_ARG_CAST_ACTUAL, __VA_ARGS__)); \
        }                                                               \
-       static inline long __##rname(UK_ARG_MAPx(x, UK_S_ARG_ACTUAL,    \
+       static inline rtype __##rname(UK_ARG_MAPx(x, UK_S_ARG_ACTUAL,   \
                                                 __VA_ARGS__))
 #define _UK_LLSYSCALL_R_DEFINE(...) __UK_LLSYSCALL_R_DEFINE(__VA_ARGS__)
 #define UK_LLSYSCALL_R_DEFINE(rtype, name, ...)                                
\
-- 
2.20.1


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