package/libkcapi: fix build due to sign conversion error of msg_iovlen

new file mode 100755
index 0000000000..535875ff4f
@@ -0,0 +1,83 @@
+From 7715c99599a5e5fb3dd962b4d433d80de09164c3 Mon Sep 17 00:00:00 2001
+From: Tan En De <[email protected]>
+Date: Sun, 6 Nov 2022 22:56:51 +0800
+Subject: [1/1] kcapi-kernel-if: fix sign conversion error for msg_iovlen
+
+uClibc and glibc both define __GLIBC__,
+but in uClibc, if __WORDSIZE == 32, msg_iovlen is of type int,
+instead of type size_t.
+
+Therefore, this patch adds checking that removes the following errors,
+which occurs when using uClibc and with __WORDSIZE=32:
+lib/kcapi-kernel-if.c: In function '_kcapi_common_send_meta':
+lib/kcapi-kernel-if.c:196:26: error: conversion to 'int' from 'size_t'
+{aka 'unsigned int'} may change the sign of the result
+[-Werror=sign-conversion]
+  196 |         msg.msg_iovlen = kcapi_downcast_int(iovlen);
+      |                          ^~~~~~~~~~~~~~~~~~
+lib/kcapi-kernel-if.c: In function '_kcapi_common_send_data':
+lib/kcapi-kernel-if.c:270:26: error: conversion to 'int' from 'size_t'
+{aka 'unsigned int'} may change the sign of the result
+[-Werror=sign-conversion]
+  270 |         msg.msg_iovlen = kcapi_downcast_int(iovlen);
+      |                          ^~~~~~~~~~~~~~~~~~
+lib/kcapi-kernel-if.c: In function '_kcapi_common_recv_data':
+lib/kcapi-kernel-if.c:568:26: error: conversion to 'int' from 'size_t'
+{aka 'unsigned int'} may change the sign of the result
+[-Werror=sign-conversion]
+  568 |         msg.msg_iovlen = iovlen;
+      |                          ^~~~~~
+
+Signed-off-by: Tan En De <[email protected]>
+---
+ lib/kcapi-kernel-if.c | 25 ++++++++++++++++++++++---
+ 1 file changed, 22 insertions(+), 3 deletions(-)
+
+diff --git a/lib/kcapi-kernel-if.c b/lib/kcapi-kernel-if.c
+index d7b10bf..5560317 100644
+--- a/lib/kcapi-kernel-if.c
++++ b/lib/kcapi-kernel-if.c
+@@ -119,7 +119,19 @@ int _kcapi_common_accept(struct kcapi_handle *handle)
+ 	return 0;
+ }
+ 
+-#ifdef __GLIBC__
++#if defined(__UCLIBC__) && __WORDSIZE == 32
++static inline int kcapi_downcast_int(size_t in)
++{
++	if (in > INT_MAX)
++		return INT_MAX;
++	return (int)in;
++}
++
++static inline socklen_t kcapi_downcast_socklen_t(size_t in)
++{
++	return (socklen_t)in;
++}
++#elif defined(__GLIBC__)
+ static inline size_t kcapi_downcast_int(size_t in)
+ {
+ 	return in;
+@@ -564,10 +576,17 @@ ssize_t _kcapi_common_recv_data(struct kcapi_handle *handle,
+ 	msg.msg_controllen = 0;
+ 	msg.msg_flags = 0;
+ 	msg.msg_iov = iov;
+-#ifdef __GLIBC__
++/*
++ * uClibc and glibc both define __GLIBC__,
++ * so we must check __UCLIBC__ before __GLIBC__.
++ * In uClibc, if __WORDSIZE == 32, msg_iovlen is of type int
++ */
++#if defined(__UCLIBC__) && __WORDSIZE == 32
++	msg.msg_iovlen = kcapi_downcast_int(iovlen);
++#elif defined(__GLIBC__)
+ 	msg.msg_iovlen = iovlen;
+ #else
+-	msg.msg_iovlen = (int)iovlen;
++	msg.msg_iovlen = kcapi_downcast_int(iovlen);
+ #endif
+ 	ret = recvmsg(*_kcapi_get_opfd(handle), &msg, 0);
+ 	if (ret < 0)
+-- 
+2.25.1
+