rsync 3.4.3 does not build on older Darwin

[debohman]

syscall.c:605:9: error: call to undeclared function 'mknodat'; ISO C99 and later do not support implicit function
      declarations [-Wimplicit-function-declaration]
  605 |                 ret = mknodat(dfd, bname, mode, dev);
      |                       ^
syscall.c:605:9: note: did you mean 'mknod'?
/usr/include/unistd.h:671:6: note: 'mknod' declared here
  671 | int      mknod(const char *, mode_t, dev_t);
      |          ^

macos 10.12.6

[devZer0]

shouldn't autoconf handle that?

[debohman]

shouldn't autoconf handle that?

I thought so. I don't understand why it is behaving as it is.

[nuclearpidgeon]

Inspecting the git blame for that syscall file https://github.com/RsyncProject/rsync/blame/v3.4.3/syscall.c , the line from your reported compile error was brought in as part of this vibe commit 2 weeks ago 30656c5. The commit / lines in question introduced a new do_mknod_at function, and also replaced two calls to do_mknod in backup.c to this new do_mknod_at function.

A quick web search suggests that Darwin doesn't support mknodat specifically: https://lists.gnu.org/archive/html/qemu-devel/2022-02/msg05987.html, https://openradar.appspot.com/FB9862426

The repo does have macOS building set up in CICD so not sure why that wouldn't have caught this same issue. However:

• The action has runs-on: macos-latest - in the runs I've looked at it seems this meant only macOS 15.7.4
• The macOS CICD doesn't appear to have run for this syscall change commit / PR specifically
• However, the macOS CICD did run fine for these two commits after the syscall changes (1, 2):
• -std=gnu23 is in the compile calls in the CICD so the c99 error should have shown up if there was a code condition to trigger it

The call to mknodat() is wrapped by this #ifdef:

#ifdef AT_FDCWD
// ...
		ret = mknodat(dfd, bname, mode, dev);
	e = errno;
	close(dfd);
	errno = e;
	return ret;
#else
	return do_mknod(pathname, mode, dev);
#endif

But I'm not familiar with where these defines come from. As @devZer0 mentioned it's most likely something that happens in the depths of Autoconf

[debohman]

Verified in rsync-3.4.4.