umask seems to be ignored on file creation

[hly2019]

Version of emscripten/emsdk:

5.0.6

A process-wide umask(0077) seems to be ignored by open(..., O_CREAT, 0666) and mkdir(). The created file keeps the raw mode instead of mode & ~umask.

Failing command line in full:

$ emcc -O0 -Wall umask.c -o a.out.js
$ node a.out.js
mode: 666 (expect 600)

The same program on native Linux prints mode: 600 (expect 600).

Example code snippet:

#include <fcntl.h>
#include <unistd.h>
#include <sys/stat.h>
#include <stdio.h>

int main(void) {
    mkdir("/tmp/xsv_test", 0755);
    umask(0077);
    int fd = open("/tmp/xsv_test/f.txt", O_WRONLY | O_CREAT | O_TRUNC, 0666);
    write(fd, "x", 1);
    close(fd);

    struct stat st;
    stat("/tmp/xsv_test/f.txt", &st);
    printf("mode: %o (expect 600)\n", st.st_mode & 0777);
    return ((st.st_mode & 0777) == 0600) ? 0 : 1;
}