[Minios-devel] [UNIKRAFT PATCH v2 2/2] lib/uknetdev: Fix compliation warning about signed/unsigned comparision

[Jia He <justin.he@xxxxxxx>]

This fixes the compilation warning when compiling libuknetdev

/root/hj/UK/unikraft/lib/uknetdev/netbuf.c: In function
'uk_netbuf_alloc_buf':
/root/hj/UK/unikraft/lib/uknetdev/netbuf.c:120:35: warning: comparison
between signed and unsigned integer expressions [-Wsign-compare]
  if (likely(UINT16_MAX - headroom > NETBUF_ADDR_ALIGNMENT)) {
                                   ^
/root/hj/UK/unikraft/include/uk/arch/lcpu.h:48:43: note: in definition
of macro 'likely'
 #define likely(x)   (__builtin_expect((!!(x)), 1))
                                           ^

The UINT16_MAX is 0xffff (signed int) on my X86 host (gcc version 7.4.0).
Integer types smaller than int are promoted when an operation is performed
on them. Thus, the left side of equation is "int", and the right side is
size_t.

Signed-off-by: Jia He <justin.he@xxxxxxx>
---
v2: describe the root cause more clear in commit log.
    make the fix better than v1

 lib/uknetdev/netbuf.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/uknetdev/netbuf.c b/lib/uknetdev/netbuf.c
index 96a5f68..bd39c54 100644
--- a/lib/uknetdev/netbuf.c
+++ b/lib/uknetdev/netbuf.c
@@ -117,7 +117,7 @@ struct uk_netbuf *uk_netbuf_alloc_buf(struct uk_alloc *a, 
size_t buflen,
         * We can only do this if the given headroom stays within
         *  uint16_t bounds after the operation.
         */
-       if (likely(UINT16_MAX - headroom > NETBUF_ADDR_ALIGNMENT)) {
+       if (likely((size_t)(UINT16_MAX - headroom) > NETBUF_ADDR_ALIGNMENT)) {
                if (privlen == 0) {
                        priv_offset    = 0;
                        buf_offset     = sizeof(*m);
@@ -166,7 +166,7 @@ struct uk_netbuf *uk_netbuf_prepare_buf(void *mem, size_t 
size,
         * We can only do this if the given headroom stays within
         *  uint16_t bounds after the operation.
         */
-       if (likely(UINT16_MAX - headroom > NETBUF_ADDR_ALIGNMENT)) {
+       if (likely((size_t)(UINT16_MAX - headroom) > NETBUF_ADDR_ALIGNMENT)) {
                if (privlen == 0) {
                        priv_offset = 0;
                        buf_offset  = sizeof(*m);
-- 
2.17.1


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