On Wed, Jun 12, 2024 at 12:29 PM Alejandro Colomar [off-list ref] wrote:

Hi Paul,

On Wed, Jun 12, 2024 at 07:55:14AM GMT, Paul Eggert wrote:

quoted

On 2024-06-12 05:16, Alejandro Colomar wrote:

quoted

tcgets.c:53:24:
  error: implicit conversion changes signedness: 'int' to 'tcflag_t' (aka
  'unsigned int') [clang-diagnostic-sign-conversion,-warnings-as-errors]

This is a bug in Clang not glibc, and if you're worried about it I suggest
sending a bug report to the Clang folks about the false positive.

Even GCC's -Wsign-conversion, which is at least smart enough to not warn
about benign conversions like that, is too often so chatty that it's best
avoided.

A lot of this stuff is pedanticism that dates back to the bad old days when
the C standard allowed ones' complement and signed magnitude representations
of signed integers. Although it can be amusing to worry about that
possibility (I know I've done it) it's never been a practical worry, and
even the motivation of pedanticism is going away now that C23 requires two's
complement.

I know; I think I have -Weverything enabled in that run, which is known
for its pedanticity.  I usually disable it when it triggers a warning,
since they are usually nonsense.  But in this case, adding U is a net
improvement, without downsides (or I can't see them).

well, any change like this is a potential source incompatibility ... i
hacked these changes into AOSP, and it did break one bit of existing
code that was already working around the sign differences --- this
warning was enabled but the code had a cast to make the _other_ side
of the comparison signed (rather than make this side of the comparison
unsigned).

Android's libc [bionic] uses the uapi headers directly, so we would be
affected, but to be clear --- i'm fine with this if the consensus is
to go this way.

(but, yeah, i'm with the "how about we fix the language and compiler
rather than all the extant code?" sentiment from Paul Eggert.)

So, while the kernel and glibc are just fine with this implicit
conversion, they would be equally fine and even better without the
conversion.  Not a bug, but rather a slight improvement.

Have a lovely day!
Alex

--
<https://www.alejandro-colomar.es/>