OS X sigaction错误地设置了sa_mask

#include <stdio.h>
#include <signal.h>

static void nop(int unused) { }

int
main(void) {
    struct sigaction sa,osa;
    sigset_t mask;

    sigemptyset(&sa.sa_mask);
    printf("Errno after sigempty sa_mask: %dn",errno);
    sigemptyset(&osa.sa_mask);
    printf("Errno after sigempty oldsa_mask: %dn",errno);
    sa.sa_flags = 0;
    sa.sa_handler = nop;

    sigprocmask(0,NULL,&mask);
    printf("Errno after sigprocmask mask: %dn",errno);
    printf("%dn",sigismember(&mask,SIGALRM));

    sigaction(SIGALRM,&sa,&osa);
    printf("Errno after sigaction sa osa: %dn",sigismember(&osa.sa_mask,SIGALRM));
    printf("%dn",sigismember(&sa.sa_mask,SIGALRM));

    return 0;
}

神秘印刷：

Errno after sigempty sa_mask: 0
Errno after sigempty oldsa_mask: 0
Errno after sigprocmask mask: 0
0
Errno after sigaction sa osa: 0
1
0

我希望osa的sa_mask成员匹配sigprocmask给出的掩码.

POSIX是否指定了该字段的任何要求？在联机帮助页中唯一提到的是关于SIGKILL等不可阻塞的信号,其中该值未指定.

在linux上,这个程序打印：

Errno after sigempty sa_mask: 0
Errno after sigempty oldsa_mask: 0
Errno after sigprocmask mask: 0
0
Errno after sigaction sa osa: 0
0
0

正如所料.

gcc版本是：

$gcc --version
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 6.0 (clang-600.0.54) (based on LLVM 3.5svn)
Target: x86_64-apple-darw

二进制文件链接到：

/usr/lib/libSystem.B.dylib (compatibility version 1.0.0,current version 1197.1.1)