Doesn't anyone care about this? Or is it that everyone hasn't encountered this problem? Why do these two warnings occur every time I compiled?
On 2020/9/1 16:39, Zhen Lei wrote: > samples/seccomp/user-trap.c is compiled with $(userccflags), and the > latter does not contain -fno-strict-aliasing, so the warnings reported as > below. Due to add "userccflags += -fno-strict-aliasing" will impact other > files, so use __attribute__((__may_alias__)) to suppress it exactly. > > My gcc version is 5.5.0 20171010. > > ---------- > samples/seccomp/user-trap.c: In function ‘send_fd’: > samples/seccomp/user-trap.c:50:2: warning: dereferencing type-punned pointer > will break strict-aliasing rules [-Wstrict-aliasing] > *((int *)CMSG_DATA(cmsg)) = fd; > ^ > samples/seccomp/user-trap.c: In function ‘recv_fd’: > samples/seccomp/user-trap.c:83:2: warning: dereferencing type-punned pointer > will break strict-aliasing rules [-Wstrict-aliasing] > return *((int *)CMSG_DATA(cmsg)); > ^ > > Signed-off-by: Zhen Lei <[email protected]> > --- > samples/seccomp/user-trap.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/samples/seccomp/user-trap.c b/samples/seccomp/user-trap.c > index 20291ec6489f31e..e36696b7f41517f 100644 > --- a/samples/seccomp/user-trap.c > +++ b/samples/seccomp/user-trap.c > @@ -23,6 +23,8 @@ > > #define ARRAY_SIZE(x) (sizeof(x) / sizeof(*(x))) > > +typedef int __attribute__((__may_alias__)) __int_alias_t; > + > static int seccomp(unsigned int op, unsigned int flags, void *args) > { > errno = 0; > @@ -47,7 +49,7 @@ static int send_fd(int sock, int fd) > cmsg->cmsg_level = SOL_SOCKET; > cmsg->cmsg_type = SCM_RIGHTS; > cmsg->cmsg_len = CMSG_LEN(sizeof(int)); > - *((int *)CMSG_DATA(cmsg)) = fd; > + *(__int_alias_t *)CMSG_DATA(cmsg) = fd; > msg.msg_controllen = cmsg->cmsg_len; > > if (sendmsg(sock, &msg, 0) < 0) { > @@ -80,7 +82,7 @@ static int recv_fd(int sock) > > cmsg = CMSG_FIRSTHDR(&msg); > > - return *((int *)CMSG_DATA(cmsg)); > + return *(__int_alias_t *)CMSG_DATA(cmsg); > } > > static int user_trap_syscall(int nr, unsigned int flags) >
