Have working TTY tests on CI

[mizvekov]

Some tests try to open /dev/tty, but that doesn't work on CI environment.

For example, osx_select_many_fds built with UBSAN fails with:

/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.2.sdk/usr/include/sys/_types/_fd_def.h:93:4: runtime error: index 47 out of bounds for type '__int32_t[32]' (aka 'int[32]')
    #0 0x100e2ff74 in uv__stream_osx_select stream.c:177
    #1 0x18ab96030 in _pthread_start+0x84 (libsystem_pthread.dylib:arm64e+0x7030)
    #2 0x18ab90e38 in thread_start+0x4 (libsystem_pthread.dylib:arm64e+0x1e38)

SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.2.sdk/usr/include/sys/_types/_fd_def.h:93:4 in

But even if we fix that, we can't prevent regressions as CI does not cover this test.

[bnoordhuis]

The bug here is that fd_set on macos is limited to file descriptors < 1,024 and it's trying to add file descriptor 1,500 or thereabouts.

It's possible to redefine that limit with -DFD_SETSIZE=<n> but that's at best a stop-gap measure. It's an inescapable fact of life that fd_sets have an upper limit.

We can't switch to poll(2) however because not all file descriptors work correctly with it (and that's exactly the reason why uv__stream_osx_select exists, to handle file descriptors that don't work well with poll or kqueue) so stop-gap measure it is: #4273

[vtjnash]

Looks like posix-compatibility requires it to be limited, but -D_DARWIN_UNLIMITED_SELECT will disable that limit, which is non-compliant with posix but clearly better

[bnoordhuis]

So, it turns out libuv is already compiled with -D_DARWIN_UNLIMITED_SELECT=1 (and has been since practically forever.)

My best guess is that ubsan's runtime component is unaware of that fact and assumes fd_set only has room for 1,024 file descriptors. I don't have a macbook myself anymore to test on but the warning can probably be suppressed. PR welcome.

[mizvekov]

I don't think ubsan is hardcoded with specific array sizes used in OS implementation.

It tests common undefined behavior based on language rules. It has a very low chance of having a false negative, the code often is invalid and can likely be trivially fixed, but happenstance and compiler implementation details might make it so an issue is not observed in practice.

I might have bandwidth to take a look at this UBSAN issue in detail.

But I apologize for the confusion: this ticket was created with the intention of getting to the bottom of why we don't run TTY tests on CI. I mentioned the UBSAN problem as a motivation, if we fix the UBSAN issue, we can better demontrate the fix, and prevent future regressions.