Fix sigaddset/sigdelset bit-fiddling math #23502
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I feel like we should |
Yeah, this is programmer error, and users are very likely to just be passing in |
alexrp
reviewed
Apr 8, 2025
alexrp
reviewed
Apr 9, 2025
alexrp
approved these changes
Apr 9, 2025
The code was using u32 and usize interchangably, which doesn't work on 64-bit systems. This: `pub const sigset_t = [1024 / 32]u32;` is not consistent with this: `const shift = @as(u5, @intcast(s & (usize_bits - 1)));` However, normal signal numbers are less than 31, so the bad math doesn't matter much. Also, despite support for 1024 signals in the set, only setting signals between 1 and NSIG (which is mostly 65, but sometimes 128) is defined. The existing tests only exercised signal numbers in the first 31 bits so they didn't trip over this: The C library `sigaddset` will return `EINVAL` if given an out of bounds signal number. I made the Zig code just silently ignore any out of bounds signal numbers. Moved all the `sigset` related declarations next to each in the source, too. The `filled_sigset` seems non-standard to me. I think it is meant to be used like `empty_sigset`, but it only contains 31 set signals, which seems wrong (should be 64 or 128, aka `NSIG`). It's also unused. The oddly named but similar `all_mask` is used (by posix.zig) but sets all 1024 bits (which I understood to be undefined behavior but seems to work just fine). For comparison the musl `sigfillset` fills in 65 bits or 128 bits.
alexrp
approved these changes
Apr 10, 2025
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The code was using
u32andusizeinterchangably, which doesn't work on 64-bit systems. This:pub const sigset_t = [1024 / 32]u32;is not consistent with this:const shift = @as(u5, @intCast(s & (usize_bits - 1)));However, normal signal numbers are less than 31, so the bad math doesn't matter much. Also, despite support for 1024 signals in the set, only setting signals between 1 and
NSIG(which is mostly 65, but sometimes 128) is defined. The existing tests only exercised signal numbers in the first 31 bits so they didn't trigger the overflow.The C library
sigaddsetwill returnEINVALif given an out of bounds signal number. I made the Zig code just silently ignore any out of bounds signal numbers.I moved all the
sigsetrelated declarations to be adjacent in the source, too.The
filled_sigsetseems non-standard to me. I think it is meant to be used likeempty_sigset, but it only contains 31 set signals, which seems wrong (should be 64 or 128, akaNSIG). It's also unused. The oddly named but similarall_maskis used (byposix.zig) but sets all 1024 bits (which I understood to be undefined behavior but seems to work just fine). For comparison the muslsigfillsetonly fills in 64 bits (or 128 bits).