On 2023-06-04 14:59:13+0200, Willy Tarreau wrote:
Hi Zhangjin,
On Sun, Jun 04, 2023 at 01:34:29PM +0800, Zhangjin Wu wrote:
most of the library routines share the same code model, let's add some macros to simplify the coding and shrink the code lines too.
One added for syscall return, one added for syscall call, both of them can get the typeof 'return value' automatically.
To get the return type of syscalls, __auto_type is better than typeof(), but it is not supported by the old compilers (before 2013, see [1]), so, use typeof() here.
Signed-off-by: Zhangjin Wu falcon@tinylab.org
tools/include/nolibc/sys.h | 15 +++++++++++++++ 1 file changed, 15 insertions(+)
diff --git a/tools/include/nolibc/sys.h b/tools/include/nolibc/sys.h index 1d6f33f58629..937a8578e3d4 100644 --- a/tools/include/nolibc/sys.h +++ b/tools/include/nolibc/sys.h @@ -28,6 +28,21 @@ #include "errno.h" #include "types.h" +/* Syscall call and return helpers */ +#define __syscall_ret(ret) \ +({ \
- if (ret < 0) { \
SET_ERRNO(-ret); \ret = (typeof(ret))-1; \- } \
- ret; \
+})
+#define __syscall(name, ...) \ +({ \
- typeof(sys_##name(__VA_ARGS__)) ret = sys_##name(__VA_ARGS__); \
- __syscall_ret(ret); \
+})
Well, I personally don't find that it increases legibility, on the opposite. At first when reading the series, I thought you had dropped errno setting on return. I think the reason is that when reading that last macro, it's not at all obvious that __syscall_ret() is actually modifying this ret value *and* returning it as the macro's result.
If we'd want to go down that route, I suspect that something like this would at least hint about what is being returned:
+#define __syscall(name, ...) \ +({ \
- typeof(sys_##name(__VA_ARGS__)) ret = sys_##name(__VA_ARGS__); \
- ret = __syscall_ret(ret); \
+})
But I'm interested in others' opinion on this, particularly Thomas and Arnd who review a significant number of patches. For now I prefer not to take it before we've settled on a choice.
While I see the value in factoring out this pattern I'm also not really happy with the implementation. Especially the magic delegation to "sys_##name".
What about something like this:
static inline long __ret_as_errno(long ret) /* or some other name */ { if (ret < 0) { SET_ERRNO(-ret); ret = -1; } return ret; }
This avoids another macro by using a normal function.
Syscall return values should always fit into long, at least extrapolating from syscall(2) and the fact that they are returned in registers.
It would be a bit more verbose:
int chdir(const char *path) { return __ret_as_errno(sys_chdir(path)); }
But it's clear what's going on and also just one line.
Thomas