Missing openat syscall is blocking grep

[rishabhBudhouliya]

Issue

Currently, we stub the openat syscall with SYSCALL_CANCEL which is causing grep to fail as it uses openat with AT_FDCWD flag.

lind-wasm/src/glibc/sysdeps/unix/sysv/linux/openat.c

Lines 30 to 41 in a91b430

	__libc_openat (int fd, const char *file, int oflag, ...)
	{
	mode_t mode = 0;
	if (__OPEN_NEEDS_MODE (oflag))
	{
	va_list arg;
	va_start (arg, oflag);
	mode = va_arg (arg, mode_t);
	va_end (arg);
	}
	return SYSCALL_CANCEL (openat, fd, file, oflag, mode);

Proposed fix:

I already tested grep successfully by adding

  if (fd == AT_FDCWD)
      return __libc_openat (file, oflag, mode);

to

• src/glibc/sysdeps/unix/sysv/linux/openat.c
• src/glibc/sysdeps/unix/sysv/linux/openat64.c
• src/glibc/sysdeps/unix/sysv/linux/openat_nocancel.c
• src/glibc/sysdeps/unix/sysv/linux/openat64_nocancel.c

@rennergade and @Yaxuan-w wanted your advice on whether this is the right approach to fix this problem or should we implement openat syscall at RawPOSIX level?